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You’re cooking dinner and are just about to reach for the potatoes. Do you grab a peeler too? What if I told you that this is a nutritional blunder of epic proportions, and you’re basically throwing the most valuable part of your produce into the bin?
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Smoothies are my go-to meal when I want to get a lot of nutrients with minimal effort—so naturally, I have one a day now. And it wasn’t until this last year that I locked down how to make one that’s actually filling, tastes like a sweet treat, supports my muscles, and doesn’t spike my blood sugar.
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“We sort of have our cultural picture of what loneliness is, you know, maybe an older person who’s isolated. Actually, loneliness refers to the absence of quality relationships, just as I mean, the cliché is true. You can be lonely in a crowd,” Hotz says.
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Ranked as the ninth leading cause of mortality globally and contributing to more than one million annual deaths, it’s no wonder that the prevention and management of Type 2 diabetes, blood glucose spikes, and insulin resistance is a high priority in public health.
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If you’re trying to watch your blood sugar, chances are you’re mindful of your fruit intake. It seems counterintuitive to steer clear of whole, nutrient-rich foods like mangoes and citrus, but some fruits just aren’t the best for those with blood sugar concerns.
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In fact, watermelon rinds have been used since ancient Egyptian times, registered dietitian Ella Davar, R.D., CDN, tells mbg. With a rising awareness of environmental sustainability and zero-waste movements, though, she says eating the rind is becoming more mainstream.
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What can shift workers do to moderate the adverse effects of circadian rhythm disruption?
Shift workers may have higher rates of death from heart disease, stroke, diabetes, dementia, and cardiovascular disease, as well as higher rates of death from cancer. Graveyard shift, indeed! But, is it just because they’re eating out of vending machines or not getting enough sleep? Highly controlled studies have recently attempted to tease out these other factors by putting people on the same diets with the same sleep—but at the wrong time of day. Redistributing eating to the nighttime resulted in elevated cholesterol and increases in blood pressure and inflammation. No wonder shift workers are at higher risk. Shifting meals to the night in a simulated night-shift protocol effectively turned about one-third of the subjects prediabetic in just ten days. Our bodies just weren’t designed to handle food at night, as I discuss in my video The Metabolic Harms of Night Shifts and Irregular Meals.
Just as avoiding bright light at night can prevent circadian misalignment, so can avoiding night eating. We may have no control over the lighting at our workplace, but we can try to minimize overnight food intake, which has been shown to help limit the negative metabolic consequences of shift work. When we finally do get home in the morning, though, we may disproportionately crave unhealthy foods. In one experiment, 81 percent of participants in a night-shift scenario chose high-fat foods, such as croissants, out of a breakfast buffet, compared to just 43 percent of the same subjects during a control period on a normal schedule.
Shiftwork may also leave people too fatigued to exercise. But, even at the same physical activity levels, chronodisruption can affect energy expenditure. Researchers found that we burn 12 to 16 percent fewer calories while sleeping during the daytime compared to nighttime. Just a single improperly-timed snack can affect how much fat we burn every day. Study subjects eating a specified snack at 10:00 am burned about 6 more grams of fat from their body than on the days they ate the same snack at 11:00 pm. That’s only about a pat and a half of butter’s worth of fat, but it was the identical snack, just given at a different time. The late snack group also suffered about a 9 percent bump in their LDL cholesterol within just two weeks.
Even just sleeping in on the weekends may mess up our metabolism. “Social jetlag is a measure of the discrepancy in sleep timing between our work days and free days.” From a circadian rhythm standpoint, if we go to bed late and sleep in on the weekends, it’s as if we flew a few time zones west on Friday evening, then flew back Monday morning. Travel-induced jet lag goes away in a few days, but what might the consequences be of constantly shifting our sleep schedule every week over our entire working career? Interventional studies have yet put it to the test, but population studies suggest that those who have at least an hour of social jet lag a week (which may describe more than two-thirds of people) have twice the odds of being overweight.
If sleep regularity is important, what about meal regularity? “The importance of eating regularly was highlighted early by Hippocrates (460–377 BC) and later by Florence Nightingale,” but it wasn’t put to the test until the 21st century. A few population studies had suggested that those eating meals irregularly were at a metabolic disadvantage, but the first interventional studies weren’t published until 2004. Subjects were randomized to eat their regular diets divided into six regular eating occasions a day or three to nine daily occasions in an irregular manner. Researchers found that an irregular eating pattern can cause a drop in insulin sensitivity and a rise in cholesterol levels, as well as reduce the calorie burn immediately after meals in both lean and obese individuals. The study participants ended up eating more, though, on the irregular meals, so it’s difficult to disentangle the circadian effects. The fact that overweight individuals may overeat on an irregular pattern may be telling in and of itself, but it would be nice to see such a study repeated using identical diets to see if irregularity itself has metabolic effects.
Just such a study was published in 2016: During two periods, people were randomized to eat identical foods in a regular or irregular meal pattern. As you can see in the graph below and at 4:47 in my video, during the irregular period, people had impaired glucose tolerance, meaning higher blood sugar responses to the same food.
They also had lower diet-induced thermogenesis, meaning the burning of fewer calories to process each meal, as seen in the graph below and at 4:55 in my video.
The difference in thermogenesis only came out to be about ten calories per meal, though, and there was no difference in weight changes over the two-week periods. However, diet-induced thermogenesis can act as “a satiety signal.” The extra work put into processing a meal can help slake one’s appetite. And, indeed, “lower hunger and higher fullness ratings” during the regular meal period could potentially translate into better weight control over the long term.
The series on chronobiology is winding down with just two videos left in this series: Shedding Light on Shedding Weight and Friday Favorites: Why People Gain Weight in the Fall.
If you missed any of the other videos, see the related posts below.
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Michael Greger M.D. FACLM
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Ancient types of wheat, like kamut, are put to the test for inflammation, blood sugar, and cholesterol control.
The number one killer in the United States and around the world is what we eat. As you can see in the graph below and at 0:15 in my video Friday Favorites: Are Ancient Grains Healthier?, our diet kills millions more than tobacco. What are the five most important things we can do to improve our diets, based on the single most comprehensive global study of the health impact of nutrition? Eat less salt, eat more nuts, eat more non-starchy vegetables, eat more fruit, and, finally, eat more whole grains.
Any particular type of whole grains? What about so-called ancient grains? Are they any better than modern varieties? For instance, what about kamut, described as “mummy wheat” and supposedly unearthed from an Egyptian tomb?
After WWII, the wheat industry selected particularly high-yielding varieties for pasta and bread. Over the past few years, though, some of the more ancient grains—“defined as those species that have remained unchanged over the last hundred years” despite agricultural revolutions—have been reintroduced to the market.
As you can see below and at 1:13 in my video, nutritionally, kamut and einkorn wheat, which is the oldest wheat, have more eyesight-improving yellow carotenoid pigments, such as lutein and zeaxanthin, compared to modern bread and pastry wheat, because the pigments have been bred out of the bread intentionally. People want their white bread white, but modern pasta flour (durum wheat) maintains much of that yellow nutritional hue.
As you can see in the graph below and at 1:41 in my video, modern wheat may have less lutein, but it tends to have more vitamin E, as seen in the graph below and at 1:45. Based on straight vitamin and mineral concentrations, it’s pretty much a wash. Both modern and primitive kinds of wheat have a lot of each, but primitive wheats do have more antioxidant capacity, likely due to their greater polyphenol content, as you can see in the graph below and at 2:00 in my video. To know if that makes any difference, though, we have to put it to the test.
If you expose human liver cells to digested bread made out of ancient grains (kamut and spelt), heritage kinds of wheat, or modern strains, then expose the cells to an inflammatory stimulus, the modern wheat strains seem less able to suppress the inflammation, as you can see in the graphs below and at 2:09 in my video. The investigators conclude that even though these different grains seem to be very similar nutritionally, they appear to exert different effects on human cells, “confirming the potential health benefits of ancient grains.” 
That was in a petri dish, though. What about people? If ancient kinds of wheat are better at suppressing inflammation, what if you took people with irritable bowel syndrome (IBS) and randomized them to receive six weeks of wheat products made out of modern wheat or ancient wheat—in this case, kamut? Same amount of wheat, just different types. If there is no difference between the wheats, there’d be no difference in people’s symptoms, right? But, when study participants in the control group were switched to the ancient wheat kamut, they experienced less abdominal pain, less frequent pain, less bloating, more satisfaction with stool consistency, and less interference with their quality of life, compared to the modern wheat. So, after switching to the ancient wheat, they had “a significant global improvement in the extent and severity of symptoms related to IBS…”
What about liver inflammation? The liver function of those with nonalcoholic fatty liver disease randomized to eat kamut improved, compared to those eating the same amount of regular wheat, suggesting kamut is superior, as you can see below and at 3:47 in my video.
People with diabetes, had better cholesterol and better insulin sensitivity on the same ancient grain, as shown below and at 3:57.
And those with heart disease? They had better blood sugar control and better cholesterol, as shown below and at 4:03.
And, people without overt heart disease had better artery function, as you can see below and at 4:06 in my video.
The bottom line is that findings derived from human studies suggest that ancient wheat products are more anti-inflammatory and may improve things like blood sugar control and cholesterol. “Given that the overall number of human interventional trials conducted to date are numerically insufficient, it is not possible to definitively conclude that ancient wheat varieties are superior to all commercial, modern wheat counterparts in reducing chronic disease risk.” However, the best available data do suggest they’re better for us.
Regardless of what type of wheat you may eat, a word to the wise: Don’t eat the plastic bread-bag clip. A 45-year-old man presented with bloody stools, and his CT scan showed the offending piece of plastic from his bag of bread, as you can see below and at 4:53 in my video. When the patient was questioned, he “admitted to habitually eating quickly without chewing properly.”
Whole grains—ideally intact ones and ancient and modern varieties alike—are an integral part of my Daily Dozen checklist, the healthiest of healthy things I encourage everyone to try to fit into their daily routines.
Whole grains are especially good for our microbiome. Learn more in the related posts below. What about gluten? Also, see the related posts below.
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Michael Greger M.D. FACLM
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Registered Dietitian Nutritionist
Molly Knudsen, M.S., RDN is a Registered Dietician Nutritionist with a bachelor’s degree in nutrition from Texas Christian University and a master’s in nutrition interventions, communication, and behavior change from Tufts University. She lives in Newport Beach, California, and enjoys connecting people to the food they eat and how it influences health and wellbeing.
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The same meal eaten at the wrong time of day can double blood sugar.
We’ve known for more than half a century that our glucose tolerance—the ability of our body to keep our blood sugars under control—declines as the day goes on. As you can see in the graph below and at 0:25 in my video How Circadian Rhythms Affect Blood Sugar Levels, if you hook yourself up to an IV and drip sugar water into your vein at a steady pace throughout the day, your blood sugars will start to go up at about 8:00 pm, even though you haven’t eaten anything and the infusion rate didn’t change.
The same amount of sugar is going into your system every minute, but your ability to handle it deteriorates in the evening before bouncing right back in the morning. A meal eaten at 8:00 pm can cause twice the blood sugar response as an identical meal eaten at 8:00 am, as shown in the graph below and at 0:51 in my video. It’s as if you ate twice as much. Your body just isn’t expecting you to be eating when it’s dark outside. Our species may have only discovered how to use fire about a quarter million years ago. We just weren’t built for 24-hour diners.
One of the tests for diabetes is called the glucose tolerance test, which sees how fast our body can clear sugar from our bloodstream. You swig down a cup of water with about four and a half tablespoons of regular corn syrup mixed in, then have your blood sugar measured two hours later. By that point, your blood sugar should be under 140 mg/dL. Between 140 and 199 is considered to be a sign of prediabetes, and 200 and up is a sign of full-blown diabetes, as you can see in the graph below and at 1:37 in my video.
The circadian rhythm of glucose tolerance is so powerful that a person can test normal in the morning but as a prediabetic later in the day. Prediabetics who average 163 mg/dL at 7:00 am may test out as frank diabetics at over 200 mg/dL at 7:00 pm, as you can see in the graph below and at 1:53 in my video.
Choosing lower glycemic foods may help promote weight loss, but timing is critical. Due to this circadian pattern in glucose tolerance, a low-glycemic food at night can cause a higher blood sugar spike than a high-glycemic food eaten in the morning, as you can see below and at 2:05 in my video.
We’re so metabolically crippled at night that researchers found that eating a bowl of All Bran cereal at 8:00 pm caused as high a blood sugar spike as eating Rice Krispies at 8:00 am, as you can see in the graph below and at 2:23 in my video.
High glycemic foods at night would seem to represent the worst of both worlds. So, if you’re going to eat refined grains and sugary junk, it might be less detrimental in the morning, as you can see in the graph below and at 2:32 in my video.
The drop in glucose tolerance over the day could therefore help explain the weight-loss benefits of frontloading calories towards the beginning of the day. Even just taking lunch earlier versus later may make a difference, as you can see in the graph below and at 2:48 in my video.
People randomized to eat a large lunch at 4:30 pm suffered a 46 percent greater blood sugar response compared to an identical meal eaten just a few hours earlier at 1:00 pm. A meal at 7:00 am can cause 37 percent lower blood sugars than an identical meal at 1:00 pm, as you can see below, and at 3:04 in my video.
Now, there doesn’t seem to be any difference between a meal at 8:00 pm and the same meal at midnight; they both seem to be too late, as you can see below, and at 3:15 in my video.
But, eating that late, at midnight or even 11:00 pm, can so disrupt your circadian rhythm that it can mess up your metabolism the next morning, resulting in significantly higher blood sugars after breakfast, compared to eating the same dinner at 6:00 pm the evening before, as shown in the graph below and at 3:32 in my video.
So, these revelations of chronobiology bring the breakfast debate full circle. Skipping breakfast not only generally fails to cause weight loss, but it worsens overall daily blood sugar control in both diabetic individuals and people who are not diabetic, as you can see in the graph below and at 3:44 in my video.
Below and at 3:53, you can see a graph showing how the breakfast skippers have higher blood sugars even while they’re sleeping 20 hours later. This may help explain why those who skip breakfast appear to be at higher risk of developing type 2 diabetes in the first place.
Breakfast skippers also tend to have higher rates of heart disease, as well as having higher rates of atherosclerosis, in general. Is this just because “skipping breakfast tends to cluster with other unhealthy choices, including smoking” and sicklier eating habits overall? The link between skipping breakfast and heart disease—even premature death in general—seems to survive attempts to control for these confounding factors, but you don’t really know until you put it to the test.
Does skipping breakfast lead to higher cholesterol, for example? Yes, researchers found a significant rise in LDL (bad) cholesterol in study participants randomized to skip breakfast; they were about 10 points higher within just two weeks, as you can see below and at 4:45 in my video.
The Israeli study with the caloric distribution of 700 calories for breakfast, 500 for lunch, and 200 for dinner that I’ve discussed previously found that the triglycerides of the king-prince-pauper group (those eating more at breakfast versus dinner) got significantly better—a 60-point drop—while those of the pauper-prince-king group got significantly worse (a 26-point rise). So, consuming more calories in the morning relative to the evening may actually have a triple benefit: more weight loss, better blood sugar control, and lower heart disease risk, as you can see below and at 5:18 in my video.
If you’re going to skip any meal, whether you’re practicing intermittent fasting or time-restricted feeding (where you try to fit all of your food intake into a certain time window each day), it may be safer and more effective to skip dinner rather than breakfast.
I’m back with the next installment of the chronobiology series! I previously explored eating breakfast for weight loss (Is Breakfast the Most Important Meal for Weight Loss? and Is Skipping Breakfast Better for Weight Loss?), introduced chronobiology (How Circadian Rhythms Can Control Your Health and Weight), and looked at the science on eating more in the mornings than the evenings (Eat More Calories in the Morning to Lose Weight, Breakfast Like a King, Lunch Like a Prince, Dinner Like a Pauper, and Eat More Calories in the Morning Than the Evening).
Next, you’ll see How to Sync Your Central Circadian Clock to Your Peripheral Clocks.
The series will wrap up in the next couple of weeks. See videos and blogs in related posts below.
Note: The Israeli 700/500/200 study that I mentioned is detailed in the Breakfast Like a King, Lunch Like a Prince, Dinner Like a Pauper video if you want to know more. Also, check the corresponding blog in related posts.
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Michael Greger M.D. FACLM
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As dietitians, people are often quite curious about what we put on our plates. We know so much about food and nutrition that every meal must be picture-perfect: Right? Not quite. But we do practice what we preach, and each of us has a few nonnegotiable healthy choices that are staples in our daily lives.
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When most people think about reducing their diabetes risk, their minds go straight to diet. And while it’s true that the foods you eat have a significant impact on your blood sugar, insulin control, and risk for Type 2 diabetes, they’re not the only factor to pay attention to. New research shows that your sleep patterns can also influence your Type 2 diabetes risk—regardless of what’s on your plate.
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What you eat and drink can be the potential cause of autoimmunity, or the most nourishing influence in terms of helping to prevent or reverse autoimmunity. But what principles should you keep in mind when you eat for the long term? There are four main areas to address via nutritional modulation when you have an autoimmune disease: nutritional gaps, poor digestion, toxic backlog, and blood sugar spikes. Let’s dig into the importance of each:
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Next, it’s important to be cognizant of foods that could cause a spike in blood sugar. These include simple carbohydrates (as opposed to the complex, fiber-laden types of carbohydrates you receive from whole grains, legumes, vegetables, etc.), sugary treats, and added sugars. (Generally, the more processed and refined a food is, the less it resembles the original plant source, and the faster and higher the blood glucose spike.)
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Calories eaten in the morning count less than calories eaten in the evening, and they’re healthier, too.
Time-restricted feeding, where you limit the same amount of eating to a narrow evening window, has benefits compared to eating in the evening and earlier in the day, but it also has adverse effects because you’re eating so much, so late, as you can see below and at 0:12 my video The Benefits of Early Time-Restricted Eating.
The best of both worlds was demonstrated in 2018 when researchers put time-restricted feeding into a narrow window earlier in the day. As you can see below and at 0:28 in my video, individuals who were randomized to eat the same food, but only during an 8:00 a.m. to 3:00 p.m. eating window, experienced a drop in blood pressure, oxidative stress, and insulin resistance, even when all of the study subjects were maintained at the same weight. Same food, same weight, but with different results. The drops in blood pressure were extraordinary, from 123/82 down to 112/72 in five weeks, and that is comparable to the effectiveness of potent blood-pressure drugs.
The longest study to date on time-restricted feeding only lasted for 16 weeks. It was a pilot study without a control group that involved only eight people, but the results are still worth noting. Overweight individuals, who, like most of us, had been eating for more than 14 hours a day, were instructed to stick to a consistent 10- to 12-hour feeding window of their own choosing, as you can see below and at 1:17 in my video. On average, they were able to successfully reduce their daily eating duration by about four and a half hours and had lost seven pounds within 16 weeks.
They also reported feeling more energetic and sleeping better, as seen in the graph below and at 1:32 in my video. This may help explain why “all participants voluntarily expressed an interest in continuing unsupervised with the 10-11 hr time-restricted eating regimen after the conclusion of the 16-week supervised intervention.” You don’t often see that after weight-loss studies.
Even more remarkably, eight months later and even one year post-study, they had retained their improved energy and sleep (see in the graph below and 1:55 in my video), as well as retained their weight loss (see in the graph below and 1:58 in my video)—all from one of the simplest of interventions: sticking to a consistent 10- to 12-hour feeding window of their own choosing. 
How did it work? Even though the study “participants were not overtly asked to change nutrition quality or quantity,” they appeared to unintentionally eat hundreds of fewer calories a day. With self-selected time frames for eating, you wouldn’t necessarily think to expect circadian benefits, but because they had been asked to keep the eating window consistent throughout the week, “metabolic jet lag could be minimized.” The thinking is that because people tend to start their days later on weekends, they disrupt their own circadian rhythm. And, indeed, it is as if they had flown a few time zones west on Friday evening, then flew back east on Monday morning, as you can see in the graph below and at 2:40 in my video. So, some of the metabolic advantages may have been due to maintaining a more regular eating schedule.
Early or mid-day time-restricted feeding may have other benefits as well. Prolonged nightly fasting with reduced evening food intake has been associated with lower levels of inflammation and has also been linked to better blood sugar control, both of which might be expected to lower the risk of diseases, such as breast cancer. So, data were collected on thousands of breast cancer survivors to see if nightly fasting duration made a difference. Those who couldn’t go more than 13 hours every night without eating had a 36 percent higher risk of cancer recurrence. These findings have led to the suggestion that efforts to “avoid eating after 8 pm and fast for 13 h or more overnight may be a beneficial consideration for those patients looking to decrease cancer risk and recurrence,” though we would need a randomized controlled trial to know for sure.
Early time-restricted feeding may even play a role in the health of perhaps the longest-living population in the world, the Seventh-day Adventist Blue Zone in California. As you can see in the graph below and at 3:55 in my video, slim, vegetarian, nut-eating, exercising, non-smoking Adventists live about a decade longer than the general population.
Their greater life expectancy has been ascribed to these healthy lifestyle behaviors, but there’s one lesser-known component that may also be playing a role. Historically, eating two large meals a day, breakfast and lunch, with a prolonged overnight fast, was a part of Adventist teachings. Today, only about one in ten Adventists surveyed were eating just two meals a day. However, most of them, more than 60 percent of them, reported that breakfast or lunch was their largest meal of the day, as you can see below and at 4:26 in my video. Though this has yet to be studied concerning longevity, frontloading one’s calories earlier in the day with a prolonged nightly fast has been associated with significant weight loss over time. This led the researchers to conclude: “Eating breakfast and lunch 5–6 h apart and making the overnight fast last 18–19 h may be a useful practical strategy” for weight control. The weight may be worth the wait.
For more on fasting, click here.
My big takeaway from all of the intermittent fasting research I looked at is, whenever possible, eat earlier in the day. At the very least, avoid late-night eating whenever you can. Eating breakfast like a king and lunch like a prince, with or without an early dinner for a pauper, would probably be best.
For more on fasting, fasting for disease reversal, and fasting and cancer, check the related videos below.
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Michael Greger M.D. FACLM
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Are there benefits to giving yourself a bigger daily break from eating?
The reason many blood tests are taken after an overnight fast is that meals can tip our system out of balance, bumping up certain biomarkers for disease, such as blood sugars, insulin, cholesterol, and triglycerides. Yet, as you can see in the graph below and at 0:20 in my video Time-Restricted Eating Put to the Test, fewer than one in ten Americans may even make it 12 hours without eating. As evolutionarily unnatural as getting three meals a day is, most of us are eating even more than that. One study used a smartphone app to record more than 25,000 eating events and found that people tended to eat about every three hours over an average span of about 15 hours a day. Might it be beneficial to give our bodies a bigger break?
Time-restricted feeding is “defined as fasting for periods of at least 12 hours but less than 24 hours,” and this involves trying to confine caloric intake to a set window of time, typically ranging from 3 to 4 hours, 7 to 9 hours, or 10 to 12 hours a day, which results in a daily fast lasting 12 to 21 hours. When mice are restricted to a daily feeding window, they gain less weight even when fed the same amount as mice “with ad-lib access.” Rodents have such high metabolisms, though, that a single day of fasting can starve away as much as 15 percent of their lean body mass. This makes it difficult to extrapolate from mouse models. You don’t know what happens in humans until you put it to the test.
The drop-out rates in time-restricted feeding trials certainly appear lower than most prolonged forms of intermittent fasting, suggesting it’s more easily tolerable, but does it work? Researchers found that when people stopped eating from 7:00 p.m. to 6:00 a.m. for two weeks, they lost about a pound each week compared to no time restriction. Note that “there were no additional instructions or recommendations on the amount or type of food consumed,” and no gadgets, calorie counting, or record-keeping either. The study participants were just told to limit their food intake to the hours of 6:00 a.m. and 7:00 p.m., a simple intervention that’s easy to understand and put into practice.
The next logical step? Put it to the test for months instead of just weeks. Obese men and women were asked to restrict eating to the eight-hour window between 10:00 a.m. and 6:00 p.m. Twelve weeks later, they had lost nearly seven pounds, as you can see in the graph below and at 2:18 in my video. This deceptively simple intervention may be operating from several different angles. People not only tend to eat more food later in the day, but eat higher fat foods later in the day. By eliminating eating in the late-evening hours, one removes prime-time snacking on the couch, a high-risk time for overeating. And, indeed, during the no-eating-after-7:00-p.m. study, the subjects were inadvertently eating about 250 fewer calories a day. Then, there are also the chronobiological benefits of avoiding late-night eating.
I did a whole series of videos about the role our circadian rhythms have in the obesity epidemic, how the timing of meals can be critical, and how we can match meal timing to our body clocks. Just to give you a taste: Did you know that calories eaten at dinner are significantly more fattening than the same number of calories eaten at breakfast? See the table below and at 3:08 in my video. 
Calories consumed in the morning cause less weight gain than the same calories eaten in the evening. A diet with a bigger breakfast causes more weight loss than the same exact diet with a bigger dinner, as you can see in the graph below and at 3:21 in my video, and nighttime snacks are more fattening than the same snacks if eaten in the daytime. Thanks to our circadian rhythms, metabolic slowing, hunger, carbohydrate intolerance, triglycerides, and a propensity for weight gain are all things that go bump in the night.
What about the fasting component of time-restricted feeding? There’s already the double benefit of getting fewer calories and avoiding night-time eating. Does the fact that you’re fasting for 11 or 16 hours a day play any role, considering the average person may only make it about 9 hours a day without eating? How would you design an experiment to test that? What if you randomized people into two groups and had both groups eat the same number of calories a day and also eat late into the evening, but one group fasted even longer, for 20 hours? That’s exactly what researchers at the USDA and National Institute of Aging did.
Men and women were randomized to eat three meals a day or fit all of those same calories into a four-hour window between 5:00 p.m. and 9:00 p.m., then fast the rest of the day. If the weight-loss benefits from the other two time-restricted feeding studies were due to the passive calorie restriction or avoidance of late-night eating, then, presumably, both of these groups should end up the same because they’re both eating the same amount and they’re both eating late. That’s not what happened, though. As you can see below and at 4:49 in my video, after eight weeks, the time-restricted feeding group ended up with less body fat, nearly five pounds less. They got about the same number of calories, but they lost more weight.
As seen below and at 5:00 in my video, a similar study with an eight-hour eating window resulted in three more pounds of fat loss. So, there does seem to be something to giving your body daily breaks from eating around the clock.
Because that four-hour eating window in the study was at night, though, the participants suffered the chronobiological consequences—significant elevations in blood pressure and cholesterol levels—despite the weight loss, as you can see below and at 5:13 in my video. The best of both worlds was demonstrated in 2018: early time-restricted feeding, eating with a narrow window earlier in the day, which I covered in my video The Benefits of Early Time-Restricted Eating.
Isn’t that mind-blowing about the circadian rhythm business? Calories in the morning count less and are healthier than calories in the evening. So, if you’re going to skip a meal to widen your daily fasting window, skip dinner instead of breakfast.
If you missed any of the other videos in this fasting series, check out the related videos below.
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Michael Greger M.D. FACLM
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Eating every other day can raise your cholesterol.
Are there any downsides to fasting every other day? For example, might go all day without eating impair your ability to think clearly? Surprisingly, as I discuss in my video Is Alternate-Day Intermittent Fasting Safe?, the results appear to be “equivocal.” Some studies show no measurable effects and the ones that do fail to agree on which cognitive domains are affected. Might the cycles of fasting and feasting cause eating disorder–type behaviors, like bingeing? So far, no harmful psychological effects have been found. In fact, there may be some benefit. However, the studies that have put it to the test specifically excluded those with a documented history of eating disorders, for whom the effects may differ.
What about bone health? No change in bone mineral density was noted after six months of alternate-day fasting despite about 16 pounds of weight loss, which would typically result in a dip in bone mass. However, the researchers did not note any skeletal changes in the control group either, and they lost a similar amount of weight using continuous caloric restriction. They suggested this is because both groups tended to be “more physically active than the average obese American,” getting about 1,000 to 2,000 more steps a day.
Proponents of intermittent fasting suggest it can better protect lean body mass, but most of the intermittent trials have employed less accurate methods of body composition analysis, whereas the majority of continuous caloric restriction trials used “vastly more accurate techniques.” So, to date, it is not clear if there’s a difference in lean mass preservation.
Improvements in blood pressure and triglycerides have been noted on intermittent fasting regimens, though this is presumed to be due to the reduction in body fat since the effect appears to be “dependent on the amount of weight lost.” Alternate-day fasting can improve artery function, too, as you can see in the graph below and at 1:55 in my video, though it does depend on what you’re eating on the non-fasting day. For study participants randomized to an alternate-day diet high in saturated fat, their artery function worsened despite a ten-pound weight loss, whereas it improved, as expected, in the lower-fat group. The decline in artery function was presumed to be because of the pro-inflammatory nature of saturated fat.
A concern has been raised about the effects of alternate-day fasting on cholesterol. After 24 hours without food, LDL cholesterol may temporarily bump up, but this is presumably because so much fat is being released into the system by the fast. As you can see in the graph below and at 2:33 in my video, an immediate negative effect on carbohydrate tolerance may stem from the same phenomenon—the repeated elevations of free fat floating around in the bloodstream. After a few weeks, though, LDL levels start to drop as the weight comes off. However, results from the largest and longest trial of alternate-day fasting have given me pause.
A hundred obese men and women were randomized into one of three groups: alternate-day modified fasting (25 percent of their baseline calories on fasting days and 125 percent calories on eating days), continuous, daily caloric restriction (75 percent of baseline), or a control group instructed to maintain their regular diet. So, for those going into the trial eating 2,000 calories a day, they would continue to eat 2,000 calories a day in the control group. The calorie-restriction group would get 1,500 calories every day, and the intermittent-restriction group would alternate between 500 calories a day and 2,500 calories the next.
As you can see in the graph below and at 3:32 in my video, with the same overall, average, prescribed calorie cutting in the two weight-loss groups, they both lost about the same amount of weight, but, surprisingly, the cholesterol effects were different. In the continuous calorie-restriction group, the LDL levels dropped as expected compared to the control group as the pounds came off.
But, in the alternate-day modified fasting group, they didn’t, as you can see below, and at 3:55 in my video. At the end of the year, the LDL cholesterol in the intermittent fasting group ended up being 10 percent higher than in the constant calorie-restriction group—despite the same loss of body fat. Given that LDL cholesterol is a prime causal risk factor for heart disease, our number one killer—or is even the prime risk factor—this strikes a significant blow against alternate-day fasting. If you want to try it anyway, I would advise you to have your cholesterol monitored to make sure it comes down with your weight.
If you’re diabetic, you must talk with your physician about medication adjustment for any changes in diet, including fasting of any duration. Even with proactive medication reduction, advice to immediately break the fast should sugars drop too low, and weekly medical supervision, people with type 2 diabetes who fasted for even just two days a week were twice as likely to suffer from hypoglycemic episodes compared to an unfasted control group. We still don’t know the best way to tweak blood sugar medications to prevent blood sugar from dropping too low on fasting days.
Even fasting for just one day can significantly slow the clearance of some drugs (like the blood-thinning drug Coumadin) or increase the clearance of others (like caffeine). Fasting for 36 hours can cut your caffeine buzz by 20 percent. So, consultation with your medical professional before fasting is an especially good idea for anyone on any kind of medication.
If you missed it, check out Alternate-Day Intermittent Fasting Put to the Test.
So, with ambiguous cognitive, lean mass, and bone effects, plus these cholesterol findings, I wouldn’t suggest alternate-day fasting for weight loss, but dropping pounds isn’t the only thing this way of eating is purported to do. Check out Does Intermittent Fasting Increase Human Life Expectancy?.
For other types of intermittent fasting, total fasting, and more on fasting, check out the related videos below.
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Michael Greger M.D. FACLM
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How may we preserve bone and mass on a low-calorie diet?
One of the most consistent benefits of calorie restriction is that blood pressure improves in as little as one or two weeks. Blood pressure may even be normalized in a matter of weeks and blood pressure pills discontinued. Unfortunately, this can work a little too well and cause orthostatic intolerance, which can manifest as lightheadedness or dizziness upon standing and, in severe cases, may cause fainting, though staying hydrated can help.
What about loss of muscle mass? In the CALERIE trial, which I profile in my video Potential Pitfalls of Calorie Restriction, 70 percent of the body weight the subjects lost was fat and 30 percent was lean body mass. So, they ended up with an improved body composition of about 72 percent lean mass compared to 66 percent in the control group, as you can see at 0:51 in my video. And, even though leg muscle mass and strength declined in absolute terms, relative to their new body size, they generally got stronger.
Is there any way to preserve even more lean mass, particularly among older individuals who naturally tend to lose muscle mass with age? Increased protein intakes are commonly suggested, but most studies fail to find a beneficial effect on preserving muscle strength or function whether you’re young or old, active or sedentary. For example, during a 25 percent calorie restriction, researchers randomized overweight older men and women to either a normal-protein diet with 4 grams for every ten pounds of body weight or a high-protein diet with about 8 grams per ten pounds. That doubling of protein intake had no discernible effect on lean body mass, muscle strength, or physical performance. As you can see below and at 1:48 in my video, most such studies found the same lack of benefit, but when they’re all put together, one can tease out a small advantage of about one or two pounds of lean mass over an average of six months. 
Unfortunately, high protein intake during weight loss has also been found to have “profound” negative metabolic effects, including undermining the benefits of weight loss on insulin sensitivity. As you can see in the graph below and at 2:14 in my video, if you lose 20 pounds, you can dramatically improve your body’s ability to handle blood sugars, compared to subjects in a control group who maintained their weight. But, if you lose the exact same amount of weight on a high-protein diet, getting about an extra 30 grams a day, it’s like you never lost any weight at all.
Though you can always bulk back up after weight loss, the best way to preserve muscle mass during weight loss is to exercise. The CALERIE study had no structured exercise component, and, similar to bariatric surgery, about 30 percent of the weight loss was lean mass. In contrast, that proportion was only about 16 percent of The Biggest Loser contestants, chalked up to their “vigorous exercise program.” Resistance training even just three times a week can prevent more than 90 percent of lean body mass loss during calorie restriction.
The same may be true of bone loss. Lose weight through calorie restriction alone, and you experience a decline in bone mineral density in fracture risk sites, such as the hip and spine. In the same study, though, those randomized to lose weight with exercise did not suffer any bone loss. The researchers concluded: “Our results suggest that regular EX [exercise] should be included as part of a comprehensive weight loss program to offset the adverse effects of CR [caloric restriction] on bone.”
It’s hard to argue with calls for increased physical activity, but even without an exercise regimen, the “very small” drop in bone mineral density in the CALERIE trial might only increase a ten-year risk of osteoporotic fracture by about 0.2 percent. The benefits of calorie restriction revealed by the study included improvements in blood pressure and cholesterol, as you can see in the graph below and at 3:54 in my video, as well as improved mood, libido, and sleep. These would seem to far outweigh any potential risks. The fact that a reduction in calories seemed to have such wide-ranging benefits on quality of life led commentators in the AMA’s internal medicine journal to write: “The findings of this well-designed study suggest that intake of excess calories is not only a burden to our physical homeostasis [or equilibrium], but also on our psychological well-being.”
Check out my other videos on calorie restriction, fasting, intermittent fasting, and time-restricted eating in the related videos below.
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Michael Greger M.D. FACLM
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