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Tag: tag: Endurance Training

  • The Newest Endurance Supplement Is a Broccoli Shot. But Does It Work?

    Published October 29, 2025 02:45PM

    Andreas Almgren, who streaked to a new European half-marathon record of 58:41 earlier this month, swears by it. So does Cole Hocker: “Yeah, I ripped a shot before the 5K,” he said after taking gold in that event at the track and field world championships in Tokyo in September. Mads Pederson, former world cycling champion, credits it with spurring him to his best-ever 90-minute ride.

    “It” is a supplement called Nomio, a concentrated shot extracted from broccoli sprouts that has emerged as the hottest new performance-enhancer among elite endurance athletes (as Velo’s Jim Cotton recently reported). The tagline printed on the box and splashed across the company’s website is that it’s “a natural compound that reduces lactate buildup during intense physical activity.” The promise to lower lactate is reminiscent of claims about baking soda, which has swept through endurance sport over the past few years. That’s what is drawing athletes in—but the actual science behind Nomio, preliminary though it remains, suggests a more complicated and perhaps more interesting picture.

    Nomio as a Lactate Fighter

    The active ingredient in Nomio is isothiocyanates, or ITCs, which are found in cruciferous vegetables such as broccoli, kale, and cabbage. The product was developed by scientists at Sweden’s Karolinska Institute and the Swedish School of Sport and Health Sciences—by some of the same scientists who did pioneering research into the endurance-boosting abilities of the nitrates found in foods such as beets. Beet juice has turned out to be one of the very few purported sports supplements backed by robust evidence, one of just five that the International Olympic Committee gives a thumbs-up to. That parallel is encouraging: maybe another vegetable extract is ready to join the list.

    The claims on the Nomio website are all over the map. Not only will it reduce lactate, it will also lower oxidative stress and inflammation, enhance training response to create more mitochondria, and accelerate post-exercise recovery. Oh, and it will also make your legs feel lighter. That sounds suspiciously like a magical pill that makes all your wishes come true—a bargain at $28 for four doses.

    The “Science” tab on Nomio’s website offers three references for these claims:

    The first is a 2023 study led by Filip Larsen, one of Nomio’s co-founders, in which volunteers took a shot of Nomio (or a placebo) twice a day for a week while completing intense interval workouts on an exercise bike every day. The supplement reduced oxidative stress and lowered lactate levels during exercise, improved regulation of blood glucose, and extended time to exhaustion by about 12 percent in a VO2 max test (though it didn’t actually change VO2 max).

    The second study hasn’t yet been published, but is available as a preprint while it undergoes peer review. It’s also from Larsen’s group, led by Michaela Sundqvist. This time it’s a one-shot test: take a broccoli shot, then three hours later do some exercise. Once again, lactate levels were lower at a given speed or power output compared to with a placebo.

    The third study is a little more arcane. It involved stimulating individual muscle fibers in a test tube to simulate exercise. In the presence of ITCs, there was a dramatic increase in training response leading to lower oxidative stress and the creation of more mitochondria, the cellular “powerhouses” that are key to aerobic exercise. This was an independent study by David Hood, a prominent muscle physiologist at York University. And it really was independent; when I contacted Hood, he’d never heard of Nomio. But he confirmed the study’s findings: “The results were dramatic for us,” he said. His group is now running a training study in live mice with and without ITCs, with results expected in January.

    These studies are certainly suggestive, but two things are missing, from my perspective. One is direct evidence that ITCs enhance performance. Nobody wins a medal for best mitochondria or lowest lactate levels; all we really care about is whether the supplement makes athletes faster. The other is a coherent explanation of why we should expect ITCs to make athletes faster. I’ll come back to the question of evidence below, but let’s start with the why.

    Nomio’s Other Origin Story

    When I got in touch with Larsen (whose research I’ve written about previously), he explained the evolution of his thinking about ITCs in a way that made more sense to me. It’s not about lactate, or at least it wasn’t initially.

    In Larsen’s telling, the starting point was a 2021 study on overtraining. They had volunteers progressively ramp up their training over the course of three weeks, with the final week pushing them into overtraining. At that point, their mitochondria were no longer working as well, their blood sugar control was compromised, and they were slower. “This aligns well with how athletes typically feel when they train harder than they can adapt: muscles feel heavy and unresponsive, and they don’t recover between sessions as they should,” Larsen says. The culprit appeared to be a signaling pathway called Nrf2, which is a key regulator of the body’s antioxidant defenses and (as David Hood and others have shown) how it responds to training.

    With those results in mind, Larsen and his team wondered whether boosting Nrf2 might counteract the effects of overtraining. There was already a robust literature showing that ITCs boost Nrf2. “Based on that,” Larsen says, “we simply asked: ‘What happens if we give people ITC (from broccoli sprouts) while they train really hard?’”

    That question is what led to the 2023 study mentioned above. As hypothesized, ITCs seemed to protect people from oxidative stress during heavy training. But the other benefits—better blood sugar control, and especially lower lactate during exercise—were surprising. That’s what prompted the second study, where even a single dose of ITCs—as much as you’d get from about six pounds of raw broccoli, packed into a shot glass-sized container—lowered lactate during exercise.

    Larsen and his colleagues still aren’t sure why ITCs lower lactate; there are a few possible biochemical explanations, but none has been proven yet. The effects are most apparent when lactate concentrations are in an intermediate range between about 3 and 8 millimolar, which corresponds to moderately hard but not all-out paces of the type you’d see in efforts lasting between about ten minutes and a few hours. (In contrast, the biggest benefits of baking soda are thought to accrue in shorter, more intense efforts between about one and ten minutes.)

    Before these lactate findings popped up, though, the original reason for trying ITCs was to fight the oxidative stress caused by hard training. This raises a dilemma, because there’s a well-established body of evidence suggesting that taking high doses of antioxidant supplements can actually blunt the benefits of training. The basic idea is that oxidative stress is a signal that tells your body to adapt and get stronger, so suppressing that signal by taking antioxidants results in less training adaptation.

    That’s a genuine concern, Larsen says. But in this case, ITCs aren’t really antioxidants. In fact, they’re mild pro-oxidants, just like exercise itself. In both cases, generating a small amount of oxidative stress causes the body’s own antioxidant defenses, controlled by Nrf2, to kick into higher gear. So instead of eliminating training’s adaptive signal with an antioxidant, Nomio is trying to amplify that signal. Still, Larsen says, that means it’s really only useful if you’re training reasonably hard. “We also recommend that athletes only take it before hard sessions or during tougher training blocks,” Larsen says, “not before easy sessions or on rest days.”

    More specifically, the company’s recommended usage plan has two components. For the acute benefits, take one shot three hours before a race or hard workout. For the chronic adaptive benefits, take one shot daily during hard training blocks, three hours before your main workout, then take a second shot before bed on hard workout days, and no shots on rest or easy days. Given the body’s finely tuned antioxidant balance, Larsen says, “I don’t think ITC intake is useful for healthy people who don’t train.”

    But Does It Actually Work?

    Here’s where things get sticky. In the scientific papers published so far, all we have is that subjects lasted a little longer in a VO2 max test, which isn’t really comparable to a race. Emil Sjölander, one of Nomio’s co-founders, connected me with a few scientists who have done or are doing performance testing either in academia or professional cycling, but none were willing to publicly share the results of their testing.

    When I reached out to others who work with professional endurance athletes, the responses were mixed. Everyone had heard of it, and most were at least intrigued. “Their work thus far looks well-done and credible… just not a lot of it yet,” said Trent Stellingwerff, the chief performance officer at the Canadian Sports Institute Pacific, who hasn’t yet worked with any athletes using Nomio. The most skeptical person I spoke to (who asked not to be named) said the data so far seemed “weak and unconvincing,” but they are nonetheless planning a study of Nomio’s effects this fall—which is an expression of interest, if nothing else.

    The list of athletes using it, both with and without the company’s cooperation, is long and growing. Among the unpaid names Sjölander mentioned: Conner Mantz, Clayton Young, Sarah Hall, and Graham Blanks. I asked Young about his experiences, and he admitted sharing my initial confusion about what the product’s main goal is. “After reading the research papers, it seemed like much of the science targeted changes in mitochondria,” he wrote in an email. “I was then surprised to see that it was marketed more towards reducing lactic acid levels. Almost as if they wanted to simplify the marketing and label it more as a bi-carb [i.e. baking soda] alternative.”

    Still, based on the positive experiences of some of his friends and training partners, Young gave it a shot in the lead-up to the World Championships marathon in Tokyo last month, where he placed ninth despite a hard fall early in the race. “My Tokyo build was one of the best I’ve ever had, if not the best,” he wrote. “My workouts, especially my speed workouts on the track, seem to be better than ever. That being said, there are so many factors that go into training, and it’s hard to say that it all came from Nomio.”

    Elite cycling tends to be more data-driven than marathoning, and the most detailed feedback I got on Nomio was from a coach working with a UCI World Tour team, who I agreed not to name. To this coach, the promise of lower lactate was not what interested him. “Biomarkers are one thing, but to know if something really works, it’s hard to get much out of lactate testing,” he said.

    Instead, the coach was interested in how the team performed in real-world field trials, which included a mix of moderate and all-out intervals. They didn’t notice an obvious decrease in lactate levels, but most of the riders reported “a feeling that it worked,” and many notched objectively high power outputs compared to their usual training. Proof? Not really. But the team isn’t waiting for further evidence. “If we wait, somebody else will try to use the advantage,” the coach says. “So in our world, you have to be able to work even when you don’t have clear answers.”

    It’s hard to say anything more definitive than that for now. The anecdotal evidence is intriguing, but who among us can really say for sure why we’ve had a particularly good or bad day? “The first principle is that you must not fool yourself—and you are the easiest person to fool,” as Richard Feynman once said. That’s why we do studies with placebos and control groups and so on. There’s enough interest in Nomio that those studies will come—or, if they don’t, that their absence will become increasingly glaring. Until then… broccoli season continues.

    For more Sweat Science, join me on Threads and Facebook, sign up for the email newsletter, and check out my new book The Explorer’s Gene: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map.

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  • The Surprising Limits of Human Endurance

    Published October 20, 2025 01:37PM

    Back in 2019, scientists proposed a new theory of endurance. For efforts lasting more than about a day, they suggested, the ultimate limit is dictated by how much food you’re able to digest. Your heart and mind and muscles can adapt to do amazing things, but they all need fuel. The most calories you can digest seems to be about 2.5 times your resting metabolism—so that’s what limits how much physical activity you can do day after day over weeks, months, or years.

    This idea of a “metabolic ceiling” sparked lots of discussion, but it also left some open questions. Does it really apply to top-level endurance athletes—like, say, Kilian Jornet, who just finished climbing 72 1,400-foot summits and cycling 2,500 miles in just 31 days while quaffing olive oil for calories? A newly published study in Current Biology sets out to answer some of these questions, measuring calorie data from 14 world-class ultrarunners and triathletes and analyzing the training logs of notable athletes like Jornet. Here’s what they found.

    What They Did

    The study was led by Andrew Best of the Massachusetts College of Liberal Arts and Herman Pontzer of Duke University, the latter of whom was one of the key authors of the original 2019 paper. The key data in the paper comes from 14 ultra-endurance athletes who drank special isotope-labeled water that enabled the scientists to calculate exactly how many calories they were burning at different times. They collected this data during events like a six-day ultramarathon, a 24-hour record attempt, and Joe McConaughy’s 13-day FKT on the Arizona Trail. They also collected calorie data during one or more training weeks, for reasons we’ll get into below.

    The calorie data from races blew through the theorical limit of 2.5 times resting metabolism. That’s because you can afford to go into calorie debt for short periods of time, meaning that you’re burning stored fat (and sometimes muscle) and losing weight. “Joe lost tons of weight running the Arizona Trail,” Best told me. But that can’t continue indefinitely. If you’re burning 9,000 calories a day (as Jornet estimates he was during his most recent challenge) but only consuming 7,000 calories a day, you might be able to keep doing that for a month or two, but you’ll eventually hit a wall.

    That’s why Best also measured calories during training weeks. By taking at least two measurements for each runner, one during a competition or hard training week and the other during a relatively easy training week, he created a personalized formula for each runner to estimate how many calories they burn as a function of how much they’re running. Then he applied this formula to a year’s worth of training data to see how many calories they could burn over a 12-month period rather than just during a week or two of competition. That’s where the 2.5 resting metabolism limit shows up again.

    Here’s a graph showing “metabolic scope” (which is how many calories per day you’re burning expressed as a multiple of resting metabolism) for different durations:

    The longer the duration, the lower the daily calorie burn you’re able to sustain. (Photo: Current Biology)

    The dark blue circles on the left side of the graph show the direct measurements of calorie burn during training and racing. There are values as high as seven times resting metabolism, which corresponds to a one-day record attempt on a 90-mile trail.

    The light blue circles are calculated from the athletes’ training logs based on training periods of various lengths. For example, at the six-week mark (42 days), you can see a range of light blue circles between about 2.5 and 4. The circle at 4 corresponds to a runner who ran an astounding 1,989 miles over a six-week period, which is 332 miles per week. But that was during a 46-day FKT attempt on the Appalachian Trail, so clearly not a level the subject could sustain for an entire year.

    As you extend to longer durations like 30 or 52 weeks, you can see that the light blue circles all cluster around 2.5. Some are a little higher, others a little lower, but none of these elite ultra athletes are sustaining values that are significantly higher than the proposed limit.

    What about true super-elites like Kilian Jornet and triathlon star Kristian Blummenfelt? Based on their publicly available training data, along with the training hours-to-calories formula that the new study generated, Best estimates that Blummenfelt averages about 2.8 to 2.9 times his resting metabolism over the course of an entire year, while Jornet hits 2.75. So the best of the best may edge slightly above the usual limit of 2.5, but not by much.

    What It Means

    There are two interesting features in the graph I included above. The first and most important is the flat line on the right side of the graph, which corresponds to the proposed asymptote of 2.5 based on the limits of digestion. The new results bolster my confidence that this really is a consistent phenomenon. If Jornet isn’t breaking it (by much), I don’t know who is. So I was surprised, when I checked in with Herman Pontzer, to find that he’s less confident than he was in 2019 that this is an ironclad rule.

    One of his reasons is that more data has emerged from elite cyclists at Grand Tours where they seem to be burning enormous numbers of calories without losing weight—which implies that they’re absorbing a comparable number of calories. A study of seven cyclists in the Giro d’Italia, for example, found that they burned more than four times their resting metabolism over the course of 24 days without losing weight. It may be that sports scientists’ quest to produce ever-more digestible carbohydrates is enabling cyclists to push back the limits of digestibility.

    The other interesting feature in the graph is the shape of the curve on the left. You see a similar curve when you plot your speed in shorter distance (i.e. a few hours or less) races against the time elapsed, as I did for my own track times here. In that situation, the asymptote corresponds to a quantity called critical speed, which represents your long-term sustainable pace. The shape of the curve is dictated by another parameter sometimes referred to as anaerobic capacity, which you can think of (very loosely) as the amount of energy you’re able to “borrow” when running faster than critical speed before you hit a wall. Milers and other middle-distance runners tend to have a very high anaerobic capacity.

    Something has to dictate the shape of Pontzer’s multi-day energy curve, and at this point he’s not sure what that something is. Intuitively, you can think of it as analogous to anaerobic capacity: you can “borrow” a lot of calories for a short period of time, putting you way above the 2.5 line; or you can borrow a lesser amount over an extended period of time. If you want to keep going for, say, six months, you can’t really borrow anything: calories out has to be balanced by calories in.

    But what determines the shape of that curve? If you’re carrying a lot of body fat, does that enable you to borrow more for longer? Or, more likely, if you’ve trained your metabolism to burn fat more rapidly, does that raise the curve? Does the precise shape of the curve depend on the mix of fat and carbohydrate that you burn at different exercise intensities? Or are there other non-metabolic factors that come into play, like muscle recovery or mental fatigue? The physiology of multi-day endurance challenges is still a relatively young scientific field—which means there should be lots of more insights, and lots more fun, still to come.

    For more Sweat Science, join me on Threads and Facebook, sign up for the email newsletter, and check out my new book The Explorer’s Gene: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map.

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  • How Fat Makes You Fast

    How Fat Makes You Fast

    Peter Frick-Wright (host): This is the Outside Podcast.

    Peter: One of the first events at this year’s summer olympics is race walking. On August 1st, the fastest walkers in the world will toe the line to see who can move the quickest while keeping one foot in contact with the ground at all times and straightening their leading leg as the foot makes contact with the ground and keeping it straight until the leg passes under the body.

    And I know you’ve heard the jokes and seen the parodies, but… race walking is hard core. Elites walk a 6 and a half or 7-minute mile for 20 km. It’s a sport whose athletes live at the limits of endurance and pain tolerance.

    So, with the summer olympics in Paris coming up, we thought we’d replay this episode from 2019 about an Olympic race walker who signed up to participate in a nutrition study that changed his life.

     

    It’s the first of three episodes we’re doing looking at interesting aspects of this year’s Olympics. It was originally produced as part of our Sweat Science series.

     

    Peter: In the beginning, there were carbs, and they were good.

    Alex Hutchinson: It’s just inextricably connected that if you want to enhance your endurance performance, you have to carbo load.

    Frick-Wright: Runners run on carbohydrates. For the last half century, the menu for athletes has been pasta, bread, rice, and potatoes.

    Hutchinson: It’s like carbohydrates and endurance are the match made in heaven.

    Frick-Wright: But then there was fat, and some said, it was better.

    Hutchinson: In the sports world, it was in ultra running that people first started to say, Hey, I think it’s better to just go on a low carb high fat diet.

    Frick-Wright: The idea was that if you could tap into your body’s nearly endless supply of fat, use it to fuel your workouts, you’d have basically an unlimited supply of energy. You could run forever. And then athletes started going out and doing it. In 2012, Timothy Olson broke the record at the Western States 100, a trail race in the Sierra Nevada mountains. Then in 2015, Zach Bitter beat the American record for a hundred miles running on a track and eating a diet almost completely free of carbs.

    Hutchinson: It’s just totally radically rejecting everything we thought we knew about sports nutrition.

    Frick-Wright: This is Outside Sweat Science columnist Alex Hutchinson, and he was and still is covering the low carb high fat diet as it’s surged in popularity. Now it’s known as the bulletproof diet, paleo, caveman, Atkins, or the ketogenic diet. They’re not exactly the same, but they all limit carbohydrates and reject the idea that carbs should be the foundational block of the food pyramid.

    Hutchinson: So it becomes this sort of, the man versus the counterculture of —  they want you to believe that you need carbohydrates, but in reality you can set yourself free by following this new diet.

    Frick-Wright: You’ve probably heard of at least one of these name brand diets, or have a friend who stopped doing carbs at some point. And for people with certain food sensitivities, dropping carbs can actually feel like a miracle cure. And in the weight loss world, this idea has been pretty popular since the two thousands, and because so many people are seeing such great results, there’s a long standing debate about whether cutting carbs is the fastest way to lose weight and cash in on all sorts of internal health benefits.

    Hutchinson: Or is that going to, you know, give you cancer and make your head fall off and do all sorts of other bad things.

    Frick-Wright: What is new, and still very much up for debate, is whether or not a low carb, high fat diet is actually a superior nutrition plan for endurance athletes, or just an alternative.

    Hutchinson: So then we’ve got this new layer that’s not just is it good for you, but will it make you run a faster marathon or do better in your triathlon or whatever the endurance challenge that you’re contemplating.

    Frick-Wright: So today we’ve got the story of one man who was faced with an endurance challenge and was propelled to completely new heights thanks to a low carb, high fat diet, but maybe not quite in the way that proponents of the diet would like you to believe. That man is 28 year old Canadian Evan Dunfee.

    Evan Dunfee: My name is Evan Dunfee.

    Frick-Wright: The sport?

    Dunfee: I’m a Canadian race walker.

    Frick-Wright: Race walking.

    (audio from race walking broadcast): But what we see you so often is a one or two walk is going out fairly fairly fast, but then they tend to drop back.

    Frick-Wright: Evan Dunfee has dedicated two thirds of his life to the sport of racewalking, but he still has to explain what it is.

    Dunfee: Everything is the exact same as running; the aerobic components that are necessary, all that stuff is the exact same as running. The only difference is that in race walking, we have to adhere to two rules: one foot always has to remain in contact with the ground; and your front leg has to be straight at the knee from the time it touches the ground until it passes onto your body.

    Frick-Wright: If you can’t picture it, imagine elite athletes trying to run but as politely as possible with their head back, perfect posture, arms pumping, hips on a swivel. And yes, it seems kind of weird artificially make yourself slower and still call it a race. But if you think about it, that’s how swimming works too

    Hutchinson: Race-walking is like that. It’s like an out of the water version of swimming where form absolutely predominates everything. But you also have to be pushing to your physical limits.

    Frick-Wright: So you can think of race walking as the breaststroke of track and field.

    (to Dunfee) And how fast are you going? What’s an Olympic speed for a race walker?

    Dunfee: My personal best time for 50 kilometers is 3 hours and 41 minutes and 36 seconds. So roughly a 4 minute and 26 second kilometer.

    Frick-Wright: For those of you unfamiliar with the metric system, that’s fast.

    Dunfee: It would be slightly quicker than a seven minute mile. For perspective, I know the marathon is something that a lot of people can relate to. So in 2017 I walked the BMO Vancouver marathon, and walked it in 3hours, 10 minutes and 32 seconds.

    Frick-Wright: If you’re not a runner or don’t know marathon times, a three hour marathon puts you in the top 2% of everyone that runs marathons. You can qualify for Boston at three hours, five minutes. Evan nearly walked that. And the longer the race goes, the better he gets.

    Dunfee: The 50 K is my primary event. I like the longer stuff. I wish there was an even longer event.

    Frick-Wright:50 K is about 31 miles, so it’s a quintessential test of endurance, a marathon plus a little bit, and Evans always sort of gravitated to the more drawn out athletic events. As a kid he struggled at stick and ball team sports. He was an average runner and only took up race walking when his older brother had his appendix removed. He couldn’t take the impact of running. But Evan had a knack for low grade sustained effort. So pretty soon he was a really good racewalker. He set provincial records and then the Canadian under 18 record and then qualified for the Commonwealth games. Every year, he kept getting better, until it came time for the Olympics in London 2012 which is when he realized that when you start competing against the best in the world, he was kind of average — middle to back of the pack. He didn’t even make the Canadian team.

    Dunfee: I guess more than anything, I just kind of lost sight of how much hard work it actually took and took for granted getting better and better and better. When I didn’t improve for the first time was just kind of shocking more than anything else. And it was just sort of unexpected and it really rattled me. It took sort of that reaffirmation to be like, this is actually something I really want to do and it should be hard. If it’s not hard, then it’s not really worth doing. I think that that moment in London really helped solidify a bunch of those thoughts.

    Frick-Wright: He set his sights on the 2016 Olympics in Rio de Janeiro, Brazil, which meant getting serious about his training, which in 2012 meant going to Canberra to train at the Australian Institute of Sport.

    Dunfee: My teammate Inaki Gomez had gone down in 2011 and come back and was just like, this is amazing.It’s three months of summer when it would be winter otherwise. So for that reason alone, it’s great. The training environment, the people, the infrastructure there. It was just so new to us and something that we had never even really imagined existed.

    Frick-Wright: He trained with the best race walkers in the world, including Jared Talent an Australian who’d two medals in London, and he worked with Louise Burke, head of Sports Nutrition at the Institute.

    Dunfee: And so from there, I started going back pretty much when every opportunity I got. And then in the winter of 2015, Louise Burke and Jared got in touch and said, Hey look, we’re doing this supernova thing, looking at the effects of a high fat diet. Would you want to come out and do it?

    Frick-Wright: If you want to study how fuel affects endurance, race walking is an interesting sport to look at. And the reason why it has to do with how muscles can switch between types of fuels.

    Hutchinson: So there are three macronutrients: protein, fat and carbohydrate. And when you’re talking about endurance performance, protein, we can mostly ignore it. So it’s either fat or carbohydrate, and there’s been well over a century of research trying to figure out which fuel dominates, which is more important, how the body decides what to burn when.

    Frick-Wright: In general, when you’re doing easy exercise, like walking or on a light jog, you’re  burning fat. But as you speed up, the body starts drawing more and more from carbohydrates, which it turns into glucose. That’s because before the muscles can actually use fatty acids or glucose, both have to be turned into something called adenosine triphosphate or ATP. You can think of fatty acids and glucose as different kinds of crude oil and ATP is like gasoline, the thing your engine actually runs on. You’ve got a virtually bottomless supply of fat, but the process of refining it to ATP is simply too slow to keep up with your muscles’ needs when you’re really pushing hard — you can make ATP from carbohydrates twice as quickly. That’s why as the intensity of your workout increases, your body starts switching to carbohydrate.

    Hutchinson: So you’ve got this variable fuel mix that goes from virtually all fat to virtually all carbohydrate depending on how intensely you’re going.

    Frick-Wright: The exact mix for any given effort depends on a bunch of things including what you eat. So if you eat more carbohydrates, your body gets better at burning carbohydrates.

    Hutchinson: And the more fat you eat, the better your body gets at burning fat. This is well known, has been known for a long time, studies going back a century.

    Frick-Wright: So sports scientists have known for a long time that at top speed, we’re mostly burning carbs. But then in the nineties researchers started looking at whether or not you could prime the body to burn fat more quickly by giving it only fat. The theory was that by denying your body carbohydrates in training, you could force it to rely more on fat. Then in a race, you wouldn’t need to tap into your precious and limited supply of carbohydrates until the finishing sprint.

    Hutchinson: From about, let’s say 1995 to 2005, this was a huge area of research in sports science, but it just never produced the results that people expected. No one could demonstrate that it was actually better than the usual approach and around 2005 people finally figured out that if you eat a high fat diet, not only do you get way, way better at burning fat, you also get worse at burning carbohydrate. In fact, your body kind of throttles your ability to burn carbohydrate, and this is a problem if you’re a competitive athlete because it means you’ve got no finishing kick.

    Frick-Wright: In 2005, a definitive study at the University of Cape Town showed that cyclists were significantly worse at mid race sprints and surges after spending time on a high fat diet, even when using carbs for the actual tests. And for the most part that was that without carbs you didn’t have any explosive power. So everyone pretty much decided that high fat diets aren’t right for most athletes. But the thing is no one really told the athletes. They kept experimenting with cutting carbs and they seemed to like the results.

    So even after having declared the 2005 cyclists study to be the nail in the coffin of high fat diets, Louise Burke at the Australian Institute of Sport started to look for ways to test it out again. And she thought maybe you could apply the diet to an activity where there was no sprinting. What if there were an endurance sport where a brisk walk was as fast as you ever went?

    (audio from racewalking event): Dunfee, who’s been working so tremendously hard training in Switzerland — he’s been working with a psychologist and he’s somebody who has a degree in kinesiology. So he knows about human physiology as well as anything else.

    Frick-Wright: (to Dunfee) And what was your like nutrition game plan like before that — had you ever heard of the high fat diet?

    Dunfee: I had heard bits and pieces of it through my degree. My diet at that point, and probably still now, is one of those things that’s probably in the like big things that could change for the better. Training 200 kilometers a week kind of provides me an opportunity to make the excuse that I can have more donuts. And so for me, going into supernova, it was a radical change cause I basically lived off of sugar.

    Frick-Wright: The supernova experiments began in the fall of 2015. Evan joined 19 other elite race walkers in Australia and the plan was to divide them into two groups, restrict the carb intake of one of the groups for three weeks, and see if their bodies could adapt to run on fat. All their meals would be prepared for them and they would try to force their bodies to adapt, no matter how much it sucked.

    Dunfee: It was awful. For those first couple of days– that first time that I just had nothing to compare it to.

    Frick-Wright: Physically, the workouts were grueling. Even the ones that were supposed to be easy. Evan’s heart rate was higher, his times were slower and he felt terrible. But there have been several studies going back to the 1930s that have shown that with long enough to adapt, your body can run on fat. And Inuit cultures traditionally lived on what was essentially a low carb, high fat diet. But that doesn’t mean it’s easy to switch. Your body will do everything it can to convince you to take in more than the 40 grams of carbs Evan Dunfee got each day.

    Dunfee: So 40 grams of carbs is nothing — that’s two medium sized bananas, I guess.

    Frick-Wright: The first step of each training session was hard and Evan said it never got any easier.

    Dunfee: My teammate Inaki Gomez, who’s like this stoic, strong character,  after one of his long walks just ended up collapsing down beside one of the vans and just broke out into tears. And it was just inexplicable, like he didn’t know why he was doing it. He couldn’t understand why it was happening, but like it was just so emotionally draining trying to get through that training in those first couple of days, that first week.

    Frick-Wright: Mentally, it was also grueling. The supernova study had both a high carb and a low carb group and they ate their meals right next to each other.

    Dunfee: You sit down for your pasta dinner, which was zucchini pasta with a carbonara sauce. And you’re looking at this bowl and your bowls a third full and instinctively you know that you’re getting the same number of calories as the person next to you. But you look at the person next to you and they had this overflowing plate of pasta and bolonaise sauce and and even though, you know, it’s the same number of calories, it just can’t convince yourself of that. So you’re watching these guys eat and you’re just getting depressed and depression in the lightest sense of the word was an overarching feeling that a lot of guys had.

    Frick-Wright: But over the next few weeks as they continue to work out and eat fat, their bodies did start to adapt. In fact, they basically became fat burning super ovens, torching it faster than any of the researchers expected. 1.57 grams per minute at the end of a time trial. That’s like burning a half pound of fat every two and a half hours, and as they adapted, the workouts started to feel a little bit easier. Instead of being totally grueling, they were just hard and unlike a normal workout, they didn’t get any harder at the end.

    The reason for this has to do with how your body portions out energy. Carbohydrates are stored in your muscles as glycogen and you’re carrying about 2,500 calories worth of glycogen around with you at any given moment. You also have another 400 to 500 in your liver, but that’s getting into the weeds. Anyway, if you’re running around burning through your glycogen, you start getting near the end of those calories, like at the end of a workout, your body starts to complain. It hoards resources, tells you you’re done. Tries to convince you to stop and then finally you do, you bonk, because your body really doesn’t want you to get to the end of your supply of energy. But when you’re running on fat and you’re used to turning it into fuel, it never feels like it’s running out of gas because it’s not.

    Dunfee: In the overall, on the high fat diet, it was kinda just like moderately hard start to finish. Once you kind of accepted that and once you realized that it wasn’t going to get harder at the end, you became a little bit more okay with it being hard at the beginning.

    Frick-Wright: Did they get faster than when they were on carbs? No, they did not. And when you’re watching someone else eat pasta, while you pick out a bowl of zucchini, not going any faster — it’s like adding insult to injury.

    Dunfee: Nobody was sad to come off the diet. I think that’s pretty telling.

    Frick-Wright: What was it like to come off of the diet? How did it affect your performance and mood and everything?

    Dunfee: Quite funny actually. So the last day of the study, I think I weighed in at 64.1 kilos.

    Frick-Wright: If you’re wondering 64 kilos is 141 pounds.

    Dunfee: At the best of times I don’t have great self control and I tend to indulge a little bit aggressively. And so coming off of three weeks of being told exactly what I had to eat, I definitely overcompensated. So that morning, 64.1 kilos; that night after free eating all afternoon had 70 kilos.

    Frick-Wright: 70 kilos is 154 pounds, so that’s 13 pounds he gained back in a day.

    Dunfee: Definitely overdid it. Then the next morning had a 25 K walk to do and I crushed it and it felt great. It was almost immediately after coming off a diet, things felt normal again.

    Frick-Wright: But would he be any faster? Yes. It turns out he would. Kind of. More after this break.

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    Frick-Wright: Okay, so before the break, Evan had just come off the low carb diet, gorged himself on carbs, gained back 13 pounds and now it was time to race walk. And here’s where things get amazing. And stories like this are probably why the low carb, high fat diet has so many people that swear by it. Because despite all those studies in the 90s and early 2000s that showed you don’t get a performance boost from coming back on the carbs after a strict low carb diet, it sure your feels like you do. And Evan went out 10 days later and walked 50 kilometers faster than he ever had.

    Dunfee: I set a Canadian record, had a personal best by over five minutes and that came out of nowhere, I did not expect that at all. I didn’t go into the race thinking that that was on the cards. So that was a pretty big like, Oh wow. Like what happened there?

    Frick-Wright: All of a sudden he was fast, and throughout 2016, he stayed fast. By the time the Olympics rolled around, Evan was in contention for a medal.

    Hutchinson: If you’d asked me in 2014 I would have said he’s going to go to the Olympics and he’s going to come, let’s say 25th or something like that. Which is very impressive, I would slice off my right arm to come 25th at the Olympics. But I didn’t expect him to be in the conversation for a medal. And that only became a realistic possibility in the months leading up to the Olympics.

    Frick-Wright: And here, let’s pause because what happened at the Olympics is not only dramatic and amazing, but it was also something of a test for this brand new Evan. He’d had his breakout performance after coming back on the carbs following three weeks on the low carb high fat diet. But the Olympics were nine months later — any metabolic effects would be completely gone and he wasn’t going to go low carb again in preparation. So was he turning his back on a secret weapon?

    (audio from 2016 Rio Olympics): Well, hello and welcome to the Main 50 kilometer racewalking Rio 2016 Olympic game.

    Dunfee: So the 50 K race in Rio was what I was working every day in 2016 towards — that was my bread and butter. That’s where I knew I was going to have a chance. And that’s where I wanted to really fight for a medal. And I had never raced 50 K at a world championships or Olympic games where I was with the lead group. And so I wanted to get experience doing that. And so I just said, Hey, just stick with the leaders for as long as you possibly can.

    (audio from 2016 Rio Olympics): It is a very competitive field indeed.

    Dunfee: And so the race started and I put myself right there and I was feeling awesome. I was feeling great and I got carried away and I stupidly ended up walking off the front of the field and led the Olympic games, from about 25 K to about 39 K.

    (audio from 2016 Rio Olympics): The race is on for gold, silver and bronze in this Olympic walk.

    Dunfee: At 39 K I ended up having three of the guys come past me and was sitting in fourth place. Those top three guys pulled away a little bit and I kind of had this moment to sort of feeling sorry for myself. I was like, Oh, I know I’m in fourth place, that’s pretty good. The guys ahead of me, they’re too far ahead of me. I’m not going to catch them. The guys behind me, they’re too far behind me, they’re not gonna catch me. I’m probably gonna finish fourth and like, Hey, that’s cool.

    (audio from 2016 Rio Olympics): Reaching up towards the 40 kilometer mark now, Evan Dunfee still going on.

    Dunfee: Obviously fourth place at the Olympics would have been a great result and I would’ve been ecstatic with it. But I think just in that moment I just kind of was tired and not thinking straight and kind of just sort of lost sight of what my goals were.

    And then at 45 kilometers, uh, I was 18 seconds back of the third place athlete and I kinda just clicked back in. I had this moment where I was like, Hey, wait, no, no, no. You said your goal was to come here and to fight with those leaders and put yourself in a position to try to win a medal. And even if it meant you didn’t finish the race, even if you collapsed at 49 K that was fine. But what are you doing sitting back here feeling sorry for yourself? Go catch those guys. You can do this.

    (audio from 2016 Rio Olympics): The battle of the bronze is still going on.

    Dunfee: I remember looking at my legs, like come on legs, just take one more step. And they did. And so I was like, just take one more step. And again, they did. And so I just said take one more step, take one more step, take one more step, and, 4,001 hard steps later, pulled up alongside Hirooki Arai ofJapan at 49 kilometers into the race. We’re 3 hours and 37 minutes in — we’re four and a half minutes from the finish line. We’re both absolutely exhausted and we’re fighting it out for the bronze metal. So I went to go past him. He ended up passing me back. And in the process of that we got a little bit too close to each other and he ended up just sort of bumping into my shoulder a little bit. And it was such incidental contact, was really, really nothing, but 3 hours and 38 minutes into a race, every little thing was magnified. And that little bump completely threw me off my stride and my knees buckle underneath me and my legs sort of started to give out and sights.

    (audio from 2016 Rio Olympics): But he’s struggling. Dunfee — oh no.

    Frick-Wright: After the bump, the race was pretty much over. Evan went on to finish fourth, and on the video, you can see his legs give out just moments after he crosses the finish line. He really had nothing left.

    Dunfee: Collapsed at the finish line. Didn’t have a single step left in me. I kind of left everything I possibly had on the race course and I was pretty happy with that. In that moment, when I crossed the finish line, I was pretty ecstatic. Had broken my national record again, had walked 3:41. After the race, about an hour and a half after the race, Hirooki, the athlete who’d finished third was disqualified. So I became the third place athlete because of that contact. He appealed two hours later. So I was the bronze medalist for about two hours, and then his appeal was finally accepted. So he was reinstated back into third place. I was, for lack of a better word, bumped back down to fourth place. We had the right of final appeal, so we could have appealed once more and said, no, that’s the wrong decision, I think Hirooki should be disqualified, I deserved that medal. I watched the video, I went back to the village and got some food in me and had a little bit of time to think about it and knew as soon as I saw what happened and how incidental the contact was that he wasn’t an athlete who deserved to have his medal taken away from him and that there was no way to know whether I would have beaten him anyways. And it just wasn’t how I wanted to win a medal.

    Frick-Wright: So despite coming in just a technicality away from the podium, Evan still broke his personal record in that race. He’d gone faster than the race following his low carb diet and he hadn’t even gone low carb. But what if he had?

    Dunfee: That was the big question cause a number of us who were on the diet ended up racing really well. So that was what we want to investigate with Supernova 2.

    Frick-Wright: Supernova 2 took place in January 2017, and this time they did the same grueling low carb diet, but instead of cutting them loose when they started eating carbs again, researchers at the Australian Institute of Sport kept tracking their progress to see if there was some kind of metabolic aftereffect that only kicked in later.

    Dunfee: What we saw was more or less that all that happened when we came off the diet was we went back to where we were before. So basically all that happened was that  the negative effects of the diet were undone, the second we came off the diet: there was no super compensation, there was no magic advantage that the diet gave us, we were just able to get rid of the negative stuff really quickly.

    Frick-Wright: Even for racewalkers, perhaps the fat burningest Olympic sport out there, denying your body carbs and then giving them back again doesn’t create any kind of Slingshot effect, make you faster, more efficient. But then how do you explain Evan’s sudden improvement? Well, what depriving yourself of carbs does, according to Evan, is make you tougher.

    Dunfee: It was three and a half weeks of just mental fortitude training. It was three and a half weeks of just grinding it out and getting through it and knowing that I could do it. I think that’s what really I gained from the diet more so than any sort of physiological advantage that came from high fat. It was more of this like mental like, okay, I can do three and a half weeks of training and push hard every single day and just feel exhausted and feel tired and feel and have it feel awful and I can push through that and I can make it through that. That’s sort of what I gained more than anything else out of the diet.

    Frick-Wright: Instead of finishing a relatively comfortable eighth place, Evan realized he could probably finish an uncomfortable second, third, or fourth if he gave it everything. It trained his brain to be comfortable with being totally gassed. So now when it’s time to race, he goes for it.

    Dunfee: And as a result of that, I’ve blown up fairly magnificently at our last two world championships and gone from being in the lead pack at 38, 39, 40 K, to not knowing if I was going to finish the race at 45K.

    Frick-Wright: Before the diet, Evan was racing at the edge of his mental limits. Now he’s able to push all the way up against his actual physical limitations or at least get closer to them. And as we’ve seen over and over again in the series, the key to endurance is almost always a matter of tricking your brain and to not giving up, even when it’s telling the body to shut down. And training hard without any carbs is one way to get tough, but that still leaves the question of whether the low carb high fat diet can be a superior source of fuel for endurance athletes. The science continues to say no, but there’s still hundreds of athletes who say yes and that’s hard to argue with.

    Hutchinson: I think it depends who you ask. It depends on your beliefs. I think it’s fair to say that it’s a lot harder to get used to low carb than it is to get used to high carb. But you’d certainly find some people who would vehemently disagree and say that their life has been changed by low carb, high fat. They’ve felt great for the first time in their lives and if they accidentally eat a carb or eat more than a minuscule amount of carbs, it makes them feel horrible.

    Frick-Wright: What it seems to do is work for some people better than others — but when it works, those people get very attached.

    Dunfee: It was amazing when I would tweet something positive about the diet that would just be latched onto by the high fat army. And when I tweeted something negative about it, it would be latched onto by the high carb army. And it was just people preaching to their echo chamber. And for me that was super interesting. I did a podcast; someone had asked me to come on their podcast and they’d seen one of my tweets about saying I had had a singular positive experience and I tweeted about the diet. And so he asked me to come on the podcast and he thought I was going to just talk to how great the diet was and how much it improved my performance. And I started talking and he quickly realized that that wasn’t my opinion. I don’t think that podcast ever ended up airing.

    Frick-Wright: It’s pretty human to think that something that works for you will work for everyone else. And sure, when we see a top athlete claim high fat as the best way, it’s easy to buy into their theory. Their performance is proof, right? But after his experiences with supernova, Evan doesn’t think all that many people are really doing the high fat diet.

    Dunfee: I think a lot of people think they’re doing a high fat diet and they’re nowhere close.

    Frick-Wright: It’s really hard to stick to almost completely cutting out carbs. Evan thinks that most people who try it are failing at it.

    Dunfee: I think in a lot of times what ends up happening is that whenever you adhere to any sort of diet, you start eating healthier.

    Frick-Wright: If you eat healthier, you probably feel better. And when you’re expecting some kind of radical shift in energy, it’s really pretty easy to confuse those feelings with the benefits of burning fat.

    Dunfee: It was just so crazy for me to see how polarized that debate got and I think what Louise and his colleagues are trying to really promote is this idea of metabolic flexibility —  of using all of these different dietary interventions at different points.

    Frick-Wright: The next frontier is looking into whether it’s possible to improve your body’s ability to draw from both carbs and fat by denying it carbs periodically.

    Dunfee: Doing a really hard workout and then not replenishing your carbs, going onto a high fat diet for the day, and then the next day doing a really hard workout to get some sort of adaptation out of your muscles.

    Frick-Wright: The theory is that your body might adapt to be able to run well on both fuels and switch between them without too much trouble. The science isn’t finished, but metabolic flexibility may be the next big thing for elite athletes. For most of the rest of us, however, it’s probably just another reminder to pay attention, to have a balanced nutrition plan, and  stick to it. So in the end there’s still carbs, and they’re good, and there’s still fat — is it better? Well, probably not, but it might be just as good and being able to say that, that’s huge.

    Hutchinson: We’re coming to deeply ambivalent conclusion about whether low carb, high fat diets were the sort of magic behind Evan Dunfee. But I think it’s important to understand what a radical radical change it is that we can be ambivalent about this because I know for me, five years ago, if you claimed to me that low carb, high fat diets could be the way to the route to an Olympic medal for an endurance athlete, I wouldn’t have even considered it for a moment. I would have said that, look, don’t waste my time, go back to 1870 where you belong. We understand a lot about metabolism and we know that carbohydrates are the way to go. If you pin me down right now and say, what’s the best way for an Olympic athlete to prepare for the marathon? I would still say nothing has changed from my perspective, that carbs are the way to go. But I’m 100% open to the possibility or in fact, I think it’s been demonstrated that you can run a very, very good marathon on a low carb, high fat diet. I don’t necessarily think it’s better, but it’s a radical change to even acknowledge that there’s some debate about whether it might be better, and that it’s probably just as close to as good if for whatever reason you want to go that route.

    Frick-Wright: So eat fat or don’t. But remember the lesson here is that Evan Dunfee gained everything by cutting carbs, but not because he got some kind of metabolic advantage. The diet simply showed him what he was made of, gave him access to a part of himself that he didn’t know existed. In the world of endurance, there’re going to be more diets, more theories and placebos and cutting edge science that seems promising at first, and sure you can try them out and you boost your performance by a percent or two, but because of the way we’re built, the way our minds and bodies work together, the quickest way to a Dunfee type gain isn’t changing the way you eat. It’s changing the way you think.

    OUTRO

    In the five years since this episode first aired, Evan Dunfee has had some ups and downs. He won the bronze medal in the 50k race walk at the Olympics in Tokyo in 2021. In 2022 he battled a hamstring injury and finished seventh at the World Race Walking Team Championship in Muscat, Oman, then sixth at the individual World Championships in Eugene, Oregon.

    In June, 2023, the International Olympic Committee canceled his main event—the 50k—and replaced it with a mixed-gender, marathon distance team walk. They’ll walk a quarter of the distance on each handoff. His teammate will be 21-year-old Olivia Lundman. The race is Wednesday, August 7.

    This episode was written and produced by me, Peter Frick-Wright, with music, sound design, and editing by Robbie Carver.

    Special thanks to Outside’s Sweat Science columnist, Alex Hutchinson. You can find out more about Evan Dunfee and a lot of other crazy feats of endurance in his book Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance.

    The Outside Podcast is made possible by our Outside Plus members. Learn more about all the benefits of membership at outsideonline.com/podplus.

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  • The Anti-Bonk Diet

    The Anti-Bonk Diet

    Peter Frick-Wright: It might be satire, I guess. But it doesn’t read like satire. It might be a stunt, I guess, designed to start a trend by pretending there is already a trend, but if that’s it, they really didn’t think it through.

    It is an ad for Heinz Ketchup. And in this ad, the company, Heinz, writes that “runners everywhere are fueling their runs with ketchup.”

    That’s the first text that shows up on the screen. Which, OK, maybe?

    Ketchup is chock full of sugar, that’s good. Ketchup is also free at most restaurants, which might appeal to the dirtbag runner types out there. And it comes in a packet, just like energy gels, so, easy to carry with you, also good. But, that’s pretty much where the idea falls apart.

    Here’s how we know runners everywhere are not fueling their runs with ketchup.

    For starters, to get the recommended number of calories per hour, you’d need to consume something like 30 ketchup packets. One, every other minute. You’d barely have time to run.

    And if you were to eat 30 ketchup packets, that is way too much sodium. It would be an absolute gut bomb. You’d be chugging water just to keep from throwing up.

    In fact, there are a lot of reasons why runners are not fueling their runs with ketchup. The New York Times did a whole story on how this trend really isn’t a trend. Friends don’t let friends eat ketchup while running.

    But producer Maren Larsen wanted to know: If not ketchup, what should runners eat? And does any of it sound appetizing to her girlfriend?

    Kareena Tulloch: My name is Kareena Tulloch, and I am Maren Larsen’s girlfriend.

    Maren Larsen: My girlfriend. You’re my girlfriend.

    Kareena: Yeah. The Maren Larsen.

    Maren: This is my partner Kareena. She’s a strong athlete with one pretty big weakness.

    Kareena: I’ll just be out on a lovely trail run or a bike ride and be like, ‘wow, this is so pretty, this is so pretty, like, I don’t want to stop.’

    I can go farther, I can go farther, and then I’ve gone too far.

    Maren: Let me tell you about one such day when she headed out too far. That was the case one beautiful day this fall when she headed out on her bike for a training ride.

    Kareena: I was like, oh yeah, this sounds like a really good bike ride. My friend recommended it. And so, I think it was supposed to be around 40 miles, maybe. I did plan to bring snacks and I completely forgot to bring snacks.

    Maren: Didn’t you, like, have them all laid out or something?

    Kareena: Yeah, I think I, like, had them on my kitchen counter and I just completely forgot.

    Maren: Right, right. And how much water did you bring?

    Kareena: I brought one. Water bottle?

    Maren: Like, describe, like, what kind of water bottle?

    Kareena: You know the, you know, like, the water bottles that fit on your bike?.

    Maren: Yeah. So. The smallest possible.

    Kareena: Yeah. Yeah. Yep.

    Maren: Got it.

    Kareena: So, and I think I was gonna put a, like, electrolyte packet in there, and I just completely forgot. It was just water.

    Maren: You were just, like, too excited to go on your bike ride to worry about surviving it.

    Kareena: Yeah, yeah. Exactly. I was just like, oh my gosh, this sounds super fun. And so I started the bike ride.

    Maren:Kareena headed off on her 40-mile ride, and soon found herself playing leapfrog with another cyclist. She got just a tiny bit competitive, and before she knew it, she was on a longer route than she’d planned.

    Kareena:  So I think it was around 50 miles that I ended up biking that day. Basically the whole bike ride back, I was like, food, food, food, food, food, food, food. I just couldn’t stop thinking about food.

    Maren: Kareena made it home that day, but barely. She had to stop at a 7-Eleven just a few blocks from her apartment. There, she gulped down a gatorade and loaded up her bike jersey with snacks to devour the moment she got home.

    How did you feel after your little 7-Eleven feast?

    Kareena: Decadent.

    Maren: Decadent?

    Kareena: Yeah.

    Maren: Tired?

    Kareena: Yeah, I was so tired, I think I just like laid there, I laid on my couch the rest of the day.

    Maren: It’s likely that 7-eleven run narrowly saved Kareena from bonking. Bonking is a bit of endurance sports lingo that refers to what happens when your muscles completely run out of glycogen, which is what we call glucose stored in your muscles. Bonking means you’ve used up all your glycogen, and it messes you up. Both physically and mentally. It can be dangerous. And it’s unfortunately a phenomenon Kareena is all too familiar with.

    Kareena: I love being active. I just don’t know how to fuel.

    Maren: To address this problem, Kareena has tried everything over the years: everything, that is, from eating and drinking very little while exercising to forgetting to fuel entirely. Not water, not food, not gels or gummies or anything with electrolytes in it. She avoids it all, despite the super sick running hydration vest her girlfriend got her, which has two soft flasks and plenty of room for snacks.

    Just saying.

    As she branched out to the other endurance sports and her efforts grew longer, her strategy remained the same.

    Until that day on her bike.

    That near-bonk at mile 50 was a wakeup call for Kareena, because that ride was actually part of her training for her first ever triathlon: a half iron man, this summer.  And a 50-mile bike ride is just under a third of what she has ahead of her: 1.2 miles of swimming, 13.1 miles of running, and 56 miles on the bike.

    I’m really excited for you. I’m also a little nervous for you. And I think when we were talking about this, like the other day, a couple days ago, I made an analogy that I thought was really funny, which is that you are like a fancy new sports car, but you’re putting like absolute garbage in the tank, and sometimes just forgetting to put anything in the tank.

    So you’re like in the middle of a drag race that you could totally win and then you run out of gas.

    I’ve been there to see what happens when Kareena runs out of gas. One day when we were on a trip and I was working from our hotel room, she decided to occupy herself with a six-mile trail run, a very average workout for her. But she didn’t eat breakfast or lunch, and neither of us can remember her drinking much water. By the time she returned to the hotel room in the early afternoon, she was in rough shape.

    Kareena: I remember walking up the stairs to the hotel room and I was like, like, I had to stop halfway because I was getting dizzy.

    Made it back into the hotel room and just like laid down, and you like, I can’t, you made me quesadilla, I think.

    Maren: Yeah, in the hotel microwave.

    Kareena: Yeah. With like cheese and yeah.

    Maren: Didn’t  you like throw up in a trash can?

    Kareena: Oh yeah, I did. And I remember I like couldn’t stand. Like, I tried to stand up and I got like super dizzy so I just had to like sit on the couch. It’s not good. Like, I’m not proud of it.

    I’m not happy to be talking to you about like my failures, uh, and I know I need to get better at it. I just don’t really know how.

    Maren: Well, good thing your girlfriend is a podcast producer. Which means I am going to find the answer for you, because I’m worried about you dropping dead in the middle of a race.

    As my partner’s number one cheerleader, I consider it part of my job to keep her from keeling over during her triathlon. To help me accomplish that, I called up some experts.

    Abby Chan: Nutrition is important. Especially once you get into big endurance things like anything beyond, I would even say half marathon, marathon.

    Maren: This is Abby Chan.

    Abby: It is essential, and it is the number one thing that goes wrong.

    Maren: And this is Alyssa Moukheiber.

    Alyssa: A lot of us don’t have the education around like how to eat or fuel ourselves in just like a really realistic manner and we really tend to struggle.

    Maren: Both Abby and Alyssa are registered dieticians who work with athletes. You might remember them from the time they helped me demystify the suspiciously common experience of having a post-adventure craving for a cheeseburger. I asked them to come back to see if they could help Kareena. And they reassured me that she’s not alone.

    Abby: As a dietician, granted I work in this field, people come to me for help. So this is going to be a little biased, but I have yet to meet an athlete that I’m like, yeah, you’re doing a great job. You’re totally, you’re good. You’re dialed.

    Maren: For a variety of reasons, both physiological and financial, people tend to take up endurance sports as adults. Many played other sports as kids or ran shorter distances in high school or college. And maybe because of their previous experiences, beginner endurance athletes tend to think they know how to take care of themselves in competition. But they often don’t.

    Alyssa: I was talking to one of my athletes the other day and I was telling them, I’m like, one of the major beefs I have with how like specifically teenagers are getting into sports is that we’re teaching them skills.

    But we were never taught like the same emphasis of how to rehab for those skills, how to prep for those skills or how to fuel for those skills.

    Maren: As a result, lots of talented endurance athletes bonk in their first big race and don’t know why. Or they know why, but don’t know what to do about it. It’s so common it’s almost become a rite of passage.

    Next time there’s a marathon in your town, go to mile 20 and watch strong athletes that have been running 8-minute miles stop and walk. Three hours is about as long as the average person can muscle through that kind of effort without refueling.

    There’s so much most of us don’t know about nutrition. Take for example the humble calorie, the biggest number in that black Nutrition Facts box. It’s so familiar. But what actually is a calorie, anyway?

    Alyssa: Anytime I’m talking about calories with my clients, I talk about it in the term of like, what is it? It’s a unit of energy. Like an inch is a unit of measurement. A calorie is a unit of energy.

    Maren: There are a lot of different forms that energy can take, but they’re all measured using the same unit. So if you’ve ever seen a quote-unquote energy drink with “zero calories,” that’s just marketing. There’s no actual energy in that drink. Just stimulants.

    The calorie is to the human body as the gallon of gasoline is to the internal combustion engine. Calories are what make you go.

    But not all calories are the same. There are fat calories, protein calories, and calories from carbohydrates, among others. Not all of those are good mid-effort endurance fuel. And giving yourself the right kind of calories, when you need them, can mean the difference between sprinting to the finish line and sprinting to the porta potties.

    So the first thing to understand about feeding yourself during competition and training is that getting calories while you’re exercising is, in fact, not “just eating.” It’s fueling. And yes, there is a difference.

    Alyssa: I Use the term mechanical eating a lot or practical eating. Yeah, I’m not that hungry, but it would be really helpful if I ate right now, like very strategic. I think sometimes that’s where fueling can come in.

    Maren: For our purposes, the difference between eating and fueling is a matter of context. Eating is what you do in daily life when you’re hungry. Fueling is what you do during training or a race to avoid bonking where if you’re hungry, it’s already too late.

    And because of the way your body absorbs calories, much of the time, mid-effort fueling for endurance sports is actually the opposite of what’s considered balanced nutrition the rest of the time.

    Most of the time, you want calories to absorb slowly, so your body can use the energy it’s getting as it’s getting it between meals. You want a balance of nutrients, including carbohydrates, fat, and protein, plus fiber, vitamins, and minerals.

    During endurance sports, on the other hand, your body is burning energy so fast that you want calories that can be absorbed quickly. And fat, protein, and especially fiber all put the brakes on digestion, slowing it down so that the nutrients don’t all hit the bloodstream at the same time.

    Essentially, you want your energy absorption pace to match the pace you’re moving. When you’re moving slowly, you want to absorb energy slowly. When you’re trying to tackle your first-ever triathlon? Not so much. You want a lot of energy, right away. And that means carbohydrates, also known as sugars.

    But just like there are different kinds of calories that absorb at different speeds, there are different kinds of sugars too. You’ve likely heard of the big three before: glucose, fructose, and sucrose.

    Abby: All carbohydrates eventually lead to glucose. That’s basically what happens. So carbohydrates are sugar. Sugar are carbohydrates. That’s what it is. And so there’s many different types, and that’s also going to depend on how well you absorb it or digest it.

    Maren: Glucose is the simplest sugar, and it is absorbed directly into your bloodstream without additional processing. Fructose has to first be processed by your liver before it can be absorbed, making it a slower release sugar. And sucrose, the scientific name for table sugar, consists of molecules that are half fructose and half glucose, and have to be broken down by enzymes in your digestive tract before being processed, making them the slowest sugar.

    Abby: That’s really important because our system does max out on how much glucose it can absorb in a certain amount of time. So we can actually absorb more if it’s glucose and fructose,

    Maren: The key to fueling for endurance is giving your body the types of fuels it can absorb quickly. But mixing those fuels with things like protein, fat, and fiber slows down the absorption process in a multitude of different ways. And remember, that’s a good thing if you’re sitting at a desk all day. You want to absorb energy slowly. But if you’re out biking or running all day, you want food that’s as easy to digest as possible. If it’s not, well, there are consequences.

    Abby: When we’re training and exercising, our body is stressed out. Which is fine. It’s not inherently bad, but what’s going to happen is our body will start to shunt blood flow to our muscles, which therefore means our gastrointestinal tract is going to have less blood flow as well. And we need blood flow in order to digest our food. So if we don’t have blood flow and we’re just all of a sudden loading it with a heavy amount, it’s going to end up sitting in there. It can lead to more like diarrhea, nausea, all those things that aren’t super fun.

    Maren: Okay, so you’re looking for calories that you can access quickly and won’t upset your stomach, which means you want glucose, fructose, and sucrose. And in general, for efforts longer than an hour, you want to avoid fat and fiber to make sure that your body can absorb those sugars as quickly as possible.

    How much fuel do you want, though? Abby says it depends, and gives the caveat that most of the research on this has been done on cis male athletes. But she has general guidelines.

    Abby: Typically research suggests that anywhere from 30 to 60 grams of carbohydrates per hour is where we should start. Typically, I say 40 to 60. Um, if it’s going to be three or more hours, it’s typically about 60 to 90 grams of carbs. And then there’s now new research where it’s like, if it’s even within that three or even four plus hour range, anywhere from 90 to 120 grams of carbs per hour is necessary and is showing to be actually more preventative in decreasing muscle fatigue and decreasing muscle breakdown, too.

    Maren: For a half ironman triathlon like the one my partner is doing that will take six hours or more, we’re looking at upwards of 90 grams of carbs an hour. So with a little math, we can figure out that she’ll need to consume something like 600 grams of carbs during the race.

    It’s hard to overstate just how much that is. 600 grams of carbs is what you’d find in about 82 Chips Ahoy chocolate chip cookies, 106 feet of Fruit by the Foot, 17 20-ounce gatorades, or 300 Heinz ketchup packets.

    Yikes. It’s a lot of carbs. So you can see how important it is to choose something you want to eat. But it doesn’t have to be perfect. Any carbs are better than no carbs.

    And there’s one more ingredient we need to add to this equation: electrolytes.

    Alyssa: When we’re talking about electrolytes, we’re talking about sodium, potassium, calcium, and magnesium. And so a lot of times the main thing we’re looking at, especially for endurance sports is how much sodium are you getting in? And this is going to depend on the person, um, if someone’s a much heavier sweater versus not.

    Maren: Electrolytes are crucial to the chemical reactions that cause your muscles to contract and relax. If your body has enough of them on hand, it will automatically balance these levels in the bloodstream to keep everything working, but if it runs too low on sodium, potassium, calcium, or magnesium, it can cause a bunch of problems, like muscle cramps and nutrient depletion.

    But overall, sugar, salt, and water is all you need to make basic endurance fuel. It sounds pretty simple, but staring at the myriad hydration mixes, energy gels, and performance gummies at your local grocery store can quickly get overwhelming. So how do you choose? We’ll break it down, after this.

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    Maren: Even if you think you know what to look for in your endurance fuel, the sports nutrition aisle at the grocery store can be daunting. But dietitian Abby Chan says that choosing what’s right for you really just comes down to three points.

    Abby: First and foremost, what are you actually going to eat and want to eat when you don’t want to eat anything? So your preferences are going to be the most important. So if you’re going to have a goo that’s sitting in like your back pocket or in your running vest or something like that, and it’s going to sit there for months and it’s kind of just like a just in case thing, that’s probably not your preference. So I think preference is number one.

    I think second is finances. Um, endurance sports are incredibly expensive, um, and they don’t have to be. I think a lot of times we’re told that like, you need to have this specific thing, you need to have this specific performance thing in order to compete and do well, and I would say that that’s actually wrong. You know, we, as humans, we’ve been doing endurance things for a long time and we can do it in a lot of different ways.

    And then I think it leads into the third point. of like, what is your gastrointestinal tolerance, and what has your gastrointestinal training been, because that’s going to be the main indicator of if you succeed in an event or not.

    Maren: You heard that right. Abby says that your gastrointestinal training, not your physical training, will be the biggest single factor in your success on race day. So let’s take the big three she outlined—what you want to eat, what you can afford, and what you can stomach—and build a gastrointestinal training plan. Because you really can train your gut to tolerate more nutrition over time, but you have to put in the effort.

    Abby: My like main thing there is for people who have sensitive guts is like, you need to start fueling early and often.

    Maren:which I think people might think is counterintuitive because they’re like, the second I start fueling, my stomach is going to hurt, so I’m going to put it off as long as possible. And I’m pretty sure that’s what my partner does.

    Alyssa: I feel like that’s what a lot of people do.

    Maren: It’s super common to be nauseated or experience other kinds of stomach upset when you’re doing intense, prolonged exercise. Remember that your body is pulling all the blood flow it can to your muscles, shunting it away from areas it deems less important like your stomach. And digestion requires blood flow, so without it, your stomach is left literally in the lurch. Food just sits there like a rock, and it’s not long before your body tries to find a way to get it out, one end or the other.

    So, how do you train your gut to prevent this?

    Abby: Just like your muscles, we need to start training our gut to being able to allocate those blood sources effectively so that we can actually digest and run or bike or do the thing we want to do.

    Alyssa: I think that’s where it gets overwhelming for people like your partner, Maren, because it seems like sometimes going from like 0 to 100, I haven’t practiced this thing at all, like the skill of eating and it does pose like a fear risk, right? I don’t want to feel uncomfortable during this thing.

    Maren: Doing a marathon would be terrifying if you’d  never run anywhere close to that distance before, which is why you train up to it. The same is true with eating hundreds of grams of carbs while exercising. It can be intimidating if you’ve never done it before, but fueling is a skill you can learn. And the good news is that it’s much like any other kind of training: start early, start slow, and build up over time.

    Maren: So, like, in terms of training your gut, would it be a good idea, if you’ve never done something like that before, to, like, bring a little pack of gummies with you on a run, even if it’s just a training run, even if it’s just, like, six miles or whatever, and just, like, eat one gummy every ten minutes or something like that? Like, is that how you start that? Or how do you go about that?

    Alyssa: I would start in that situation. First, like moving that food. That pre-fueling closer and closer ,getting more confident with that. And then like doing something small maybe like right before your run or during right like with those gummies or during right with like Gatorade.

    So kind of practicing moving that intake a little closer while simultaneously practicing like maybe a little bit of intake on my Like actual endurance sport,

    So find something you enjoy and just start practicing eating that during your workouts. And it can be once a week if you’re feeling antsy and uncomfortable about the way that that’s going to make you feel. But if you can consistently do that for like one of your training sessions. For a week or two, then you can bring it up to two times a week and you can build that lived experience of knowing, Okay, I was hyping up in my head. This was gonna feel a certain way. It does not. Building that lived experience of your performance feeling better so you can feel confident enough to do it more frequently.

    Maren: To begin your gastrointestinal training, you have to find what fuels work for you. Remember, your preferences are the most important thing, so it’s best to first start with what you want to eat and what you can afford.

    Alyssa: There is so much variety. So like, if you’re talking about, let’s like go liquids first, right? Gatorade. The like other version of that, that would have some carbohydrate in it and have some liquid in it would be like some kind of juice. It’s going to be different. It’s not going to be exactly the same. You don’t get the electrolytes, but if you’re talking of a liquid thing that has carb in it, I would go juice. If you’re talking like the manufactured like chews or gummies, uh, gummy bears or like gummy worms or something like that, that you find really palatable.

    Maren: I’ve noticed that in the rare instances my partner does eat while exercising, she often reaches for bananas, so I asked about fruit options.

    Alyssa: Bananas or something that are a common thing you either see at races before or after, um, or a lot of people will use. And it’s because they have a good mixture of glucose and fructose. And typically because there’s a little bit more fiber, bananas can cause a little bit more gastrointestinal discomfort depending on how well you’ve trained your gut.  Raisins are a great option too.

    Maren: So, fruits and dried fruits are decent, but may actually not be the best place to start if you have an untrained stomach. There are other options besides candy, though.

    Alyssa: Honey can be really great. It has some glucose, fructose, as well as some sucrose in it. Um, and it’s very similar to like a performance sport drink in the sugar compilation of it, which is great. Um, one thing you can do is you can add a little bit of salt to it. If you want to.

    Maren: Juice, candy, honey, some fruits, these are all things you can get outside the sports nutrition aisle, and they may feel more approachable for some people, either for their palate or for their wallet. But what about those mysterious gels and gummies in the endurance fuel aisle? What makes those different?

    What are the, like, bonuses, the pluses that you’re going to get from those really specifically engineered things. that you might not get from DIY fueling options or from like, quote unquote, “real food?”

    Abby: That’s a great question. So if it’s, let’s even talk about gummies for a second because I often have a preference of Hi-Chews when I’m riding. Um, those are my favorite preferred like type of gummy thing. But what’s going to happen is if you have more of a store bought or like fruit gummy or candy or something like that, you are typically going to get about half of the amount of carbohydrates in the same amount of serving or volume. And typically either a half or two thirds less sodium in those.

    So that’s going to be the thing that you’re really paying for is you’re paying for the engineering of this, like really great electrolyte balance. You’re paying for the engineering of having a solid amount of carbohydrates in it that you don’t have to carry this huge load with you. And also you may be paying for having some caffeine added in there as well.

    Maren: Basically, if it’s marketed as endurance fuel, it’s probably going to get you more energy per ounce. It’s probably going to be more expensive, too.

    Abby: If you’re training for, say it’s an Ironman or a Half Ironman, you’re going to have a whole year of training to get to that point.

    And so, investing in all of these sports specific engineered foods that whole time, that’s a lot of money.

    Maren: Abby says you can be thrifty by using mostly generic fuels during training, rather than expensive energy gels and drinks. Just make sure that as race-day approaches you start to incorporate the high-density, engineered foods that you’ll use during the race.

    Alyssa: Race day is not the day to try like a new way of fueling yourself.

    Maren: With Alyssa and Abby’s help, the fundamentals of endurance fueling were starting to come into focus. But much like running, which sounds easy in theory but is, in my experience, much more difficult in practice, how does all of this stuff translate to the real world?

    To find out, I took my partner Kareena on a little shopping trip. First, we perused the energy drinks.

    Maren: I think the problem here is that this one says one gram of sugar.

    Kareena: Oh, that’s right. I want sugar.

    Maren: Yeah. So, like, the ones that say, like, all of these say zero calories.

    Kareena: Zero sugar.

    Maren: Zero sugar. Like, those aren’t gonna help you.

    Kareena: Yeah.

    Maren: Even though they’re in the, like, health whatever. And this one says energy. And it’s got, like, what does it say?

    Kareena: Caffeine.

    Maren: Caffeine,

    Next, the dried fruits section caught Kareena’s eye, with its health food store vibe and pictures of real fruits on the packages.

    They did say raisins are not a bad one. Let’s see. 90 calories, 22 grams of carbs, and 2 grams of fiber. So, raisins is not bad.

    Kareena: Oh, yeah. Yeah.

    Maren: Okay. Maybe you would try?

    Kareena: I would definitely try, yes.

    Maren: Raisins? Yes. Okay

    She still seemed hesitant, though, and we left the raisins on the shelf. But finally, we found something that got Kareena excited enough to try it out.

    Like, okay, what about, like, Gushers?

    Kareena: Oh my gosh.

    Maren: What’s the nutritional value of Gushers? Okay, 18 grams of carbohydrates. No, one gram of fat.

    Kareena: 40 of sodium.

    Maren: 40 of sodium. That’s actually, that’s not bad.

    Kareena: That’s so funny.

    Maren: You could crush some gushers. You want to get some gushers?

    Kareena: 100%.

    Maren: Yes, let’s get some gushers. Oh my god.

    Kareena: Wow.

    Maren: Back in the car, gushers in hand, plus some sour patch watermelon, which I just wanted for myself but turns out are also not bad on the endurance fuel front, I asked Kareena how she was feeling.

    Kareena: I’m a little excited. I think it’ll be good to finally be like responsible with my nutrition and I think it’s always felt a little too scary or unknown and now it’s like, oh no, it’s not so unknown or scary.

    Maren: It’s just math.

    Karen’s: Yeah, I love math. Who doesn’t love math?

    Maren: Alright, let’s break into some of those gushers.

    Kareena: Hell yeah.

    Peter: Maren Larsen is a regular contributor to the Outside podcast.

    Peter: Thank you to Kareena Tulloch for getting behind the mic, and to Abby Chan and Alyssa Moukheiber for sharing their nutritional knowledge.

    Abby: You can find me, @ Abby, A-B-B-Y the R-D across all socials. And you can also find me at my website, evolveflg.com.

    Alyssa: My Instagram is body peace, B-O-D-Y-P-E-A-C-E-R-D-N. So Body peace, RDN. And my website is alo, A-L-Onutrition.com, where there’s a bunch of dieticians who work with people with sports and food issues.

    Maren: This episode was written and produced by Maren Larsen, and edited by me, Peter Frick-Wright. Music and sound design by Robbie Carver.

    The Outside Podcast is made possible by our Outside Plus members. Learn more about all the benefits of membership at outsideonline.com slash pod plus.

    Maren: I feel like we’re working kind of backwards because the last interview we did was about Post effort fueling, refueling, we were talking about hamburgers, which was so much fun. Now we’re talking about mid effort fueling, maybe in like another year I’ll call you to talk about pre fueling.

    Abby: I would love that. That’d be so fun.

    Alyssa: We’ll be ready.

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