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Tag: chronobiology?

  • Seasonal Weight Gain in the Fall  | NutritionFacts.org

    Seasonal Weight Gain in the Fall  | NutritionFacts.org

    SAD doesn’t just stand for the standard American diet.

    There’s a condition known as seasonal affective disorder that is characterized by increased appetite and cravings, as well as greater sleepiness and lethargy, that begins in autumn when light exposure starts to dwindle. This now appears to represent the far end of a normal spectrum of human behavior. We appear to eat more as the days get shorter. There is a “marked seasonal rhythm” to calorie intake with greater meal size, eating rate, hunger, and overall calorie intake in the fall. 

    In preparation for winter, some animals hibernate, doubling their fat stores with autumnal abundance to deal with the subsequent scarcity of winter. Genes have been identified in humans that are similar to hibernation genes, which may help explain why we exhibit some of the same behaviors, and the autumn effect isn’t subtle. As you can see in the graph below and at 1:06 in my video Friday Favorites: Why People Gain Weight in the Fall, researchers calculated a 222-calorie difference between how many calories we consume in the fall versus the spring. This isn’t just because it’s colder, either, since we eat more in the fall than in the winter. It appears we’re just genetically programmed to prep for the deprivation of winter that no longer comes. 

    It’s remarkable that, in this day and age of modern lighting and heating, our bodies would still pick up enough environmental cues of the changing seasons to have such a major influence on our eating patterns. Unsurprisingly, bright light therapy is used to treat seasonal affective disorder, nearly tripling the likelihood of remission, compared to placebo. Though it’s never been tested directly, it can’t hurt to take the dog out for some extra morning and daytime walks in the fall to try to fend off some of the coming holiday season weight gain.

    People blame the holidays for overeating, but it may be that “rather than the holidays causing heightened intake, the seasonal heightening of intake in the fall may have caused the scheduling of holidays at that time.”

    Regardless, as you can see below and at 2:15 in my video, other “specific recommendations for the prevention of obesity and metabolic syndrome by improving the circadian system health,” based on varying degrees of evidence, include: sleeping during the night and being active during the day; sleeping enough—at least seven or eight hours a night; early to bed, early to rise; and short naps are fine. (Contrary to popular belief, daytime napping does not appear to adversely impact sleep at night.) Also recommended: avoiding bright light exposure at night; sleeping in total darkness when possible; making breakfast or lunch your biggest meal of the day; not eating or exercising right before bed; and completely avoiding eating at night. 

    This was the last video in my chronobiology series. If you missed any of the others, check out the related posts below.

    Michael Greger M.D. FACLM

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  • Phototherapy and Losing Weight  | NutritionFacts.org

    Phototherapy and Losing Weight  | NutritionFacts.org

    What did randomized controlled trials of phototherapy—bright morning light—for weight loss find? 

    If weakening our circadian rhythm can cause weight gain, might strengthening it facilitate weight loss? You may remember the child’s swing analogy I shared previously. Regular morning meals can give our cycles a little daily push, but the biggest shove comes from our exposure to bright morning light. Similarly, exposure to light at night could be analogous to nighttime eating, as you can see below and at 0:31 in my video Shedding Light on Shedding Weight. 

    Of course, we’ve had candles to illuminate our nights for 5,000 years, but flames from candles, campfires, and oil lamps are “strongly skewed towards the red end of the [light] spectrum; as a result, firelight has much less impact on circadian rhythmicity than electric light.” It’s the shorter blue wavelengths that specially set our circadian clocks. Electric lighting, which we’ve only had for a little over a century, “has gradually changed since the 1960s from an incandescent-bulb form consisting of mainly low-level yellow wavelengths to high-intensity discharge forms,” such as fluorescents and LED lights, “that contain blue wavelengths,” which are more similar to morning sunlight and have the strongest effect on our circadian rhythm.

    Using wrist meters to measure ambient light exposure, researchers found that increased exposure to light in the evening and nighttime correlated with a subsequent increased risk of developing obesity over time. This was presumed to be due to circadian misalignment, but might it instead be a sign of not sleeping as much, and maybe that’s the real reason people grew heavier? This was controlled for in a study of more than 100,000 women, which found that the odds of obesity trended with higher nighttime light exposure independent of sleep duration.

    Compared to women who reported their bedrooms at night were either too dark to see their hand in front of their face or at least dark enough that they couldn’t see across the room, those who reported their bedrooms were light enough to see across the room were significantly heavier. They weren’t all sleeping with nightlights on either. Without blackout curtains on windows, many neighborhoods may be bright enough to cause circadian disruption. Using satellite imagery, scientists have even been able to correlate higher obesity rates with brighter communities. There’s so much light at night these days that, outside of a blackout, the only Milky Way our children will likely ever see is inside a candy wrapper.

    Although sleep quantity could be controlled, what about sleep quality? Maybe people sleeping in bedrooms that aren’t as dim don’t sleep as soundly, leaving them too tired to exercise the next day, for example. You can’t know for sure if nocturnal light exposure is harmful in and of itself until you put it to the test. When that was done, those randomized to exposure to bright light for a few hours in the evenings or exposed even just for a single night suffered adverse metabolic consequences. 

    The more intriguing question then becomes: Can circadian syncing with morning bright light therapy be a viable weight-loss strategy? Insufficient morning light may be the circadian equivalent of skipping breakfast. Indoor lighting is too bright at night, but it may be too dim during the day to robustly boost our daily rhythm. Light exposure from getting outdoors in the morning, even on an overcast day, is correlated to lower body weight compared to typical office lighting, so some doctors started trying “phototherapy” to treat obesity. The first case reports began being published in the 1990s. Three out of four women lost an average of about four pounds over six weeks of morning bright light exposure, but there was no control group to confirm the effect. 

    Ten years later, the first randomized controlled trial was published. Overweight individuals were randomized to an exercise intervention with or without an hour a day of bright morning light. Compared to normal indoor lighting, the bright light group lost more body fat, but it’s possible the light just stimulated them to exercise harder. Studies show that exposure to bright light, even the day prior to exercise, may boost performance. In a handgrip endurance test, exposure to hours of bright light increased the number of contractions until exhaustion from about 770 to 860 the next day. While light-induced improvements in activity or mood can be helpful in their own right, it would be years later still before we finally learned whether the light exposure itself could boost weight loss. 

    Following an unpublished study in Norway purporting to show a dozen-pound weight-loss advantage to eight weeks of 30 minutes of daily daylight (compared to indoor lighting), researchers tried three weeks of 45 minutes of morning bright light compared to the same time sitting in front of an “ion generator” that appeared to turn on but was secretly deactivated. As you can see in the graph below and at 5:08 in my video, the three weeks of light beat out the placebo, but the average difference in body fat reduction was only about a pound. This slight edge didn’t seem to correlate with mood changes, but bright light alone can stimulate serotonin production in the human brain and cause the release of adrenaline-type hormones, both of which could benefit body fat aside from any circadian effects. 

    Regardless of the mechanism, bright morning daylight exposure could present a novel weight-loss strategy straight out of the clear blue sky.  

    I have a whole series on chronobiology. You can see all of the videos on the topic page. The last few are listed below in the related posts and help to paint the full picture of how our environment can affect our circadian rhythms.

    For more on weight loss, you can also check out my recent series in the related posts below, or browse all of my weight loss videos here. 

    Michael Greger M.D. FACLM

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  • Irregular Meals, Night Shifts, and Metabolic Harms  | NutritionFacts.org

    Irregular Meals, Night Shifts, and Metabolic Harms  | NutritionFacts.org

    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. 
     

    Michael Greger M.D. FACLM

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  • Syncing Your Brain and Body Clocks  | NutritionFacts.org

    Syncing Your Brain and Body Clocks  | NutritionFacts.org

    Exposure to bright light synchronizes the central circadian clock in our brain, whereas proper meal timing helps sync the timing of different clock genes throughout the rest of our body. 
     
    One of the most important breakthroughs in recent years has been the discovery of “peripheral clocks.” We’ve known for decades about the central clock—the so-called suprachiasmatic nucleus. It sits in the middle of our brain right above the place where our optic nerves cross, allowing it to respond to day and night. Now we also know there are semi-autonomous clocks in nearly every organ of our body. Our heart runs on a clock, our lungs run on one, and so do our kidneys, for instance. In fact, up to 80 percent of the genes in our liver are expressed in a circadian rhythm.

    Our entire digestive tract is, too. The rate at which our stomach empties, the secretion of digestive enzymes, and the expression of transporters in our intestinal lining for absorbing sugar and fat all cycle around the clock. So, too, does the ability of our body fat to sop up extra calories. The way we know these cycles are driven by local clocks, rather than being controlled by our brain, is that you can take surgical biopsies of fat, put them in a petri dish, and watch them continue to rhythm away.

    All of this clock talk is not just biological curiosity. Our health may depend on keeping all of them in sync. “Imagine a child playing on a swing.” Picture yourself pushing, but you become distracted by what’s going on around you in the playground and stop paying attention to the timing of the push. So, you forget to push or you push too early or too late. What happens? Out of sync, the swinging becomes erratic, slows, or even stops. That is what happens when we travel across multiple time zones or have to work the night shift.

    The “pusher” in this case is the light cues falling onto our eyes. Our circadian rhythm is meant to get a “push” from bright light every morning at dawn, but if the sun rises at a different time or we’re exposed to bright light in the middle of the night, this can push our cycle out of sync and leave us feeling out of sorts. That’s an example of a mismatch between the external environment and our central clock. Problems can also arise from a misalignment between the central clock in our brain and all the other organ clocks throughout our body. An extreme illustration of this is a remarkable set of experiments suggesting that even our poop can get jet lag.

    As you can see below and at 2:31 in my video How to Sync Your Central Circadian Clock to Your Peripheral Clocks, our microbiome seems to have its own circadian rhythm.

    Even though the bacteria are down where the sun doesn’t shine, there’s a daily oscillation in both bacterial abundance and activity in our colon, as you can see in the graph below and at 2:43 in my video. Interesting, but who cares? We all should. 

    Check this out: If you put people on a plane and fly them halfway around the world, then feed their poop to mice, those mice grow fatter than mice fed preflight feces. The researchers suggest the fattening flora was a consequence of “circadian misalignment.” Indeed, several lines of evidence now implicate “chronodisruption”—the state in which our central and peripheral clocks diverge out of sync—as playing a role in conditions such as premature aging and cancer, as well as ranging to others like mood disorders and obesity.

    Exposure to bright light is the synchronizing swing pusher for our central clock. What drives our internal organ clocks that aren’t exposed to daylight? Food intake. That’s why the timing of our meals may be so important. Researchers removed all external timing cues by keeping study participants under constant dim light and found that you could effectively decouple central rhythms from peripheral ones just by shifting meal times. They took blood draws every hour and biopsies of the subjects’ fat every six hours to demonstrate the resulting metabolic disarray.

    Just as morning light can help sync the central clock in our brain, morning meals can help sync our peripheral clocks throughout the rest of our body. Skipping breakfast disrupts the normal expression and rhythm of these clock genes themselves, which coincides with adverse metabolic effects. Thankfully, they can be reversed. Take a group of habitual breakfast-skippers and have them eat three meals at 8:00 am, 1:00 pm, and 6:00 pm, and their cholesterol and triglycerides improve, compared to taking meals five hours later at 1:00 pm, 6:00 pm, and 11:00 pm. There is a circadian rhythm to cholesterol synthesis in the body, too, which is also “strongly influenced by food intake.” This is evidenced by the 95 percent drop in cholesterol production in response to a single day of fasting. That’s why a shift in meal timing of just a few hours can result in a 20-point drop in LDL cholesterol, thanks to eating earlier meals, as you can see below and at 5:00 in my video. 

    If light exposure and meal timing help keep everything synced, what happens when our circumstances prevent us from sticking to a normal daytime cycle? We’ll find out in The Metabolic Harms of Night Shifts and Irregular Meals. If you’re just coming into the series, be sure to check out the related posts below.  

    Michael Greger M.D. FACLM

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  • Circadian Rhythms and Our Blood Sugar Levels  | NutritionFacts.org

    Circadian Rhythms and Our Blood Sugar Levels  | NutritionFacts.org

    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. 

    Michael Greger M.D. FACLM

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  • Morning Calories vs. Evening Calories  | NutritionFacts.org

    Morning Calories vs. Evening Calories  | NutritionFacts.org

    Why are calories eaten in the morning less fattening than calories eaten in the evening? 

    One reason calories consumed in the morning are less fattening than those eaten in the evening is that more calories are burned off in the morning due to diet-induced thermogenesis. That’s the amount of energy the body takes to digest and process a meal, given off in part as waste heat. If people are given the same meal in the morning, afternoon, or night, their body uses up about 25 percent more calories to process it in the afternoon than at night and about 50 percent more calories to digest it in the morning, as you can see below and at 0:36 in my video Eat More Calories in the Morning Than the Evening. That leaves fewer net calories in the morning to be stored as fat.

    Let’s put some actual numbers to it. A group of Italian researchers randomized 20 people to eat the same standardized meal at either 8:00 am or 8:00 pm and had them return a week later to do the opposite. So, each person had a chance to eat the same meal for breakfast and dinner. After every meal, the study participants were placed in a “calorimeter” contraption to precisely measure how many calories they were burning over the next three hours. As you can see below and at 1:18 in my video, the researchers calculated that the meal given in the morning took about 300 calories to digest, whereas the same meal given at night only used up about 200 calories to process. The meal was about 1,200 calories, but, when eaten in the morning, it ended up only providing about 900 calories compared to more like 1,000 calories at night. Same meal, same food, same amount of food, but effectively 100 fewer calories when consumed in the morning rather than at night. So, a calorie is not just a calorie. It depends on when we eat it. 

    But why do we burn more calories when eating a morning meal? Is it behavioral or biological? If you started working the graveyard shift, sleeping during the day and working all night, which meal would net you fewer calories? Would it be the “breakfast” you had at night before you went to work or the “dinner” you had in the morning before you went to bed? In other words, is it something about eating before you go to sleep that causes your body to hold onto more calories, or is it built into our circadian rhythm, where we store more calories at night regardless of what we’re doing? You don’t know until you put it to the test.

    Harvard researchers randomized people to identical meals at 8:00 am versus 8:00 pm while under simulated night shifts or day shifts. Regardless of activity level or sleeping cycle, the number of calories that were burned processing the morning meals was 50 percent higher than in the evening, as you can see in the graph below and at 2:45 in my video. So, the difference is explained by chronobiology: It’s just part of our circadian rhythm to burn more meal calories in the morning. But, why? What exactly is going on? 

    How does it make sense for our body to waste calories in the morning when we have the whole day ahead of us? 

    Our body isn’t so much wasting calories as investing them. When we eat in the morning, our body bulks up our muscles with glycogen, which is the primary energy reserve our body uses to fuel our muscles, but this takes energy. In the evening, our body expects to be sleeping for much of the next 12 hours, so rather than storing blood sugar as extra glycogen in our muscles, it preferentially uses it as an energy source, which may end up meaning we burn less of our backup fuel (body fat). In the morning, however, our body expects to be running around all day, so instead of just burning off breakfast, our body continues to dip into its fat stores while we use breakfast calories to stuff our muscles full of the energy reserves we need to move around over the day. That’s where the “inefficiency” may come from. The reason it costs more calories to process a morning meal is that, instead of just burning glucose (blood sugar) directly, our body uses up energy to string glucose molecules together into chains of glycogen in our muscles, which are then just going to be broken back down into glucose later in the day. That extra assembly/disassembly step takes energy—energy that our body takes out from the meal, leaving us with fewer calories.

    So, in the morning, our muscles are especially sensitive to insulin, rapidly pulling blood sugar out of our bloodstream to build up glycogen reserves. At night, though, our muscles become relatively insulin-resistant and resist the signal to take in extra blood sugar. So, does that mean you get a higher blood sugar and insulin spike in the evening compared to eating the same meal in the morning? Yes. As you can see in the graph below and at 5:02 in my video, in that 100-calorie-difference study, for example, blood sugars rose twice as high after the 8:00 pm meal compared to the same meal eaten in the morning.

    So, shifting the bulk of our caloric intake towards the morning would appear to have a dual benefit—more weight loss, and better blood sugar control, as shown in the graph below and at 5:12 in my video. 

    If you thought dual benefits sounded good, stay tuned for triple benefits! I dive deeper into circadian rhythms. See related posts below.

    My last few videos (see below) focus on why science points to loading your calories towards the beginning of the day.

    Michael Greger M.D. FACLM

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  • Fighting Cancer and the Common Cold with Garlic  | NutritionFacts.org

    Fighting Cancer and the Common Cold with Garlic  | NutritionFacts.org

    Raw garlic is compared to roasted, stir-fried, simmered, and jarred garlic.

    Garlic lowers blood pressure, regulates cholesterol, and stimulates immunity. I’ve talked before about its effect on heart disease risk factors, but what about immunity? Eating garlic appears to offer the best of both worlds, dampening the overreactive face of the immune system by suppressing inflammation while boosting protective immunity—for example, the activity of our natural killer cells, which our body uses to purge cells that have been stricken by viruses or cancer. “In World War II garlic was called ‘Russian Penicillin’ because, after running out of antibiotics, the soviet government turned to these ancient treatments for its soldiers,” but does it work? You don’t know until you put it to the test.

    How about preventing the common cold? As I discuss in my video Benefits of Garlic for Fighting Cancer and the Common Cold, it is perhaps “the world’s most widespread viral infection, with most people suffering approximately two to five colds per year.” In the first study “to use a double-blind, placebo-controlled design to investigate prevention of viral disease with a garlic supplement,” those randomized to the garlic suffered 60 percent fewer colds and were affected 70 percent fewer days. So, those on garlic not only had fewer colds, but they also recovered faster, suffering only one and a half days instead of five. Accelerated relief, reduced symptom severity, and faster recovery to full fitness. Interesting, but that study was done about two decades ago. What about all of the other randomized controlled trials? There aren’t any. There’s only that one trial to date. Still, the best available balance of evidence suggests that, indeed, “garlic may prevent occurrences of the common cold.”

    What about cancer? Is garlic “a stake through the heart of cancer?” As you can see below and at 2:05 in my video, various garlic supplements have been tested on cells in a petri dish or lab animals, but there weren’t any human studies to see if garlic could affect gene expression until now. 

    Researchers found that if you eat one big clove’s worth of crushed raw garlic, you get an alteration of the expression of your genes related to anti-cancer immunity within hours. You can see a big boost in the production of cancer-suppressing proteins like oncostatin when you drip garlic directly on cells in a petri dish, as shown in the graph below and at 2:25 in my video.   

    What’s more, you can also see boosted gene expression directly in your bloodstream within three hours of eating it, as seen below and at 2:34 in my video. Does this then translate into lower cancer risk?

    As you can see in the graph below and at 2:44 in my video, after putting together ten population studies, researchers found that those reporting higher consumption of garlic only had half the risk of stomach cancer.

    How do you define “high” garlic consumption? Each study was different, from a few times a month to every day. Regardless, those who ate more garlic appeared to have lower cancer rates than those who ate less, suggesting a protective effect. Stomach cancer is a leading cause of cancer-related death around the world, and garlic “is relatively cheap; the product is freely available and easy to incorporate into a daily diet in a palatable manner”—and safely, too, so why not? And, perhaps, the more, the better. 

    The only way to prove garlic can prevent cancer is to put it to the test. Thousands of individuals were randomized to receive seven years of a garlic supplement or a placebo. Those getting garlic did tend to get less cancer and die from less cancer, as you can see below and at 3:35 in my video, but the findings were not statistically significant, meaning that could have just happened by chance. 

    Why didn’t we see a more definitive result, given that garlic eaters appear to have much lower cancer rates? Well, the researchers didn’t give them garlic; they gave them garlic extract and oil pills. It’s possible that some of the purported active components weren’t preserved in supplement form. Indeed, one study of garlic supplements, for example, found that it might take up to 27 capsules to obtain the same amount of garlic goodness found in just half a clove of crushed raw garlic.  

    What happens if you cook garlic? If you compare raw chopped garlic to garlic simmered for 15 minutes, boiled for 6 minutes, or stir-fried for just 1 minute, you can get a three-fold drop in one of the purported active ingredients called allicin when you boil it, even more of a loss if you simmer it too long, and seemingly total elimination by even a single minute of stir-frying, as seen below and at 4:21 in my video. What about roasted garlic? Surprisingly, even though roasting is hotter than boiling, that cooking method preserved about twice as much. Raw garlic has the most, but it may be easier for some folks to eat two to three cloves of cooked garlic than even half a clove of raw. 

    What about pickled garlic or those jars of minced garlic packed in water or oil? Fancy, fermented black garlic? Though jarred garlic may be more convenient, they have comparatively less garlicky goodness, especially pickled garlic, and the black garlic falls far behind, as you can see in the graph below and at 5:12 in my video. 

    Can you eat too much? The garlic meta-analysis suggests there are no real safety concerns with side effects or overdosing, though that’s with internal use. You should not stick crushed garlic on your skin. It can cause irritation and, if left on long enough, can actually burn you. Wrap your knees with a garlic paste bandage or stick some on your back overnight, and you can end up burned, as seen below, and at 5:42 and 5:44 in my video.  

    Definitely don’t rub garlic on babies, even if you see an online article saying that topical garlic is good for respiratory disorders and your little one is congested. Below and at 5:57 in my video, you can see the blisters she got. The poor pumpkin! “It is crucial…to explain to patients that ‘natural’ does not equal ‘safe’…” 

    Don’t put it on your toes, don’t use it as a face mask, and don’t use it to try to get out of military service either.  

    If you just eat it like you’re supposed to, there shouldn’t be a problem. Some people can get an upset stomach if they eat too much, though, and you can’t really say there aren’t any side effects, given the “body odor and bad breath.”

    The other video I mentioned is Friday Favorites: Benefits of Garlic Powder for Heart Disease. What else can garlic do? See related posts below.

    And, for more on specific foods for fighting colds and cancer, check out related posts below. 

    Michael Greger M.D. FACLM

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  • Lose Weight by Eating More in the Morning  | NutritionFacts.org

    Lose Weight by Eating More in the Morning  | NutritionFacts.org

    A calorie is not a calorie. It isn’t only what you eat, but when you eat.

    Mice are nocturnal creatures. They eat during the night and sleep during the day. However, if you only feed mice during the day, they gain more weight than if they were fed a similar amount of calories at night. Same food and about the same amount of food, but different weight outcomes, as you can see in the graph below and at 0:18 in my video Eat More Calories in the Morning to Lose Weight, suggesting that eating at the “wrong” time may lead to disproportionate weight gain. In humans, the wrong time would presumably mean eating at night. 

    Recommendations for weight management often include advice to limit nighttime food consumption, but this was largely anecdotal until it was first studied experimentally in 2013. Researchers instructed a group of young men not to eat after 7:00 pm for two weeks. Compared to a control period during which they continued their regular habits, they ended up about two pounds lighter after the night-eating restriction. This is not surprising, given that dietary records show the study participants inadvertently ate fewer calories during that time. To see if timing has metabolic effects beyond just foreclosing eating opportunities, you’d have to force people to eat the same amount of the same food, but at different times of the day. The U.S. Army stepped forward to carry out just such an investigation.

    In their first set of experiments, Army researchers had people eat a single meal a day either as breakfast or dinner. The results clearly showed the breakfast group lost more weight, as you can see in the graph below and at 1:35 in my video. When study participants ate only once a day at dinner, their weight didn’t change much, but when they ate once a day at breakfast, they lost about two pounds a week. 

    Similar to the night-eating restriction study, this is to be expected, given that people tend to be hungrier in the evening. Think about it. If you went nine hours without eating during the day, you’d be famished, but people go nine hours without eating overnight all the time and don’t wake up ravenous. There is a natural circadian rhythm to hunger that peaks around 8:00 pm and drops to its lowest level around 8:00 am, as you can see in the graph below and at 2:09 in my video. That may be why breakfast is typically the smallest meal of the day. 

    The circadian rhythm of our appetite isn’t just behavioral, but biological, too. It’s not just that we’re hungrier in the evening because we’ve been running around all day. If you stayed up all night and slept all day, you’d still be hungriest when you woke up that evening. To untangle the factors, scientists used what’s called a “forced desynchrony” protocol. Study participants stayed in a room without windows in constant, unchanging, dim light and slept in staggered 20-hour cycles to totally scramble them up. This went on for more than a week, so the subjects ended up eating and sleeping at different times throughout all phases of the day. Then, the researchers could see if cyclical phenomena are truly based on internal clocks or just a consequence of what you happen to be doing at the time.  

    For instance, there is a daily swing in our core body temperature, blood pressure, hormone production, digestion, immune activity, and almost everything else, but let’s use temperature as an example. As you can see in the graph below and at 3:21 in my video, our body temperature usually bottoms out around 4:00 am, dropping from 98.6°F (37°C) down to more like 97.6°F (36.4°C). Is this just because our body cools down as we sleep? No. By keeping people awake and busy for 24 hours straight, it can be shown experimentally that it happens at about the same time no matter what. It’s part of our circadian rhythm, just like our appetite. It makes sense, then, if you are only eating one meal per day and want to lose weight, you’d want to eat in the morning when your hunger hormones are at their lowest level. 

    Sounds reasonable, but it starts to get weird.

    The Army scientists repeated the experiment, but this time, they had the participants eat exactly 2,000 calories either as breakfast or as dinner, taking appetite out of the picture. The subjects weren’t allowed to exercise either. Same number of calories, so the same change in weight, right? No. As you can see in the graph below and at 4:18 in my video, the breakfast-only group still lost about two pounds a week compared to the dinner-only group. Two pounds of weight loss eating the same number of calories. That’s why this concept of chronobiology, meal timing—when to eat—is so important. 

    Isn’t that wild? Two pounds of weight loss a week eating the same number of calories! That was a pretty extreme study, though. What about just shifting a greater percentage of calories to earlier in the day? That’s the subject of my next video: Breakfast Like a King, Lunch Like a Prince, Dinner Like a Pauper. First, let’s take a break from chronobiology to look at the Benefits of Garlic for Fighting Cancer and the Common Cold. Then, we’ll resume checking other videos in the related posts below.

    If you missed the first three videos in this extended series, also check out related posts below. 

    Michael Greger M.D. FACLM

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  • Milk Hormones and Female Infertility  | NutritionFacts.org

    Milk Hormones and Female Infertility  | NutritionFacts.org

    Dairy consumption is associated with years of advanced ovarian aging, thought to be due to the steroid hormones or endocrine-disrupting chemicals in cow’s milk.
     
    When it comes to the amount of steroid hormones we are exposed to in the food supply, dairy “milk products supply about 60–80% of ingested female sex steroids.” I’ve talked about the effects of these estrogens and progesterone in men and prepubescent children, and how milk intake can spike estrogen levels within hours of consumption. You can see graphs illustrating these points from 0:25 in my video The Effects of Hormones in Milk on Infertility in Women. In terms of effects on women, I’ve discussed the increased endometrial cancer risk in postmenopausal women. What about reproductive-age women? Might dairy hormones affect reproduction? 
     
    We’ve known that “dairy food intake has been associated with infertility; however, little is known with regard to associations with reproductive hormones or anovulation.” How might dairy do it? By affecting how the uterus prepares, or by affecting the ovary itself? Researchers found that women who ate yogurt or cream had about twice the risk of sporadic anovulation, meaning failure of ovulation, so some months there was no egg to fertilize at all. Now, we know most yogurt is packed with sugar these days. Even plain Greek yogurt can have more sugar than a double chocolate glazed cake donut, but the researchers controlled for that and the results remained after adjusting for the sugar content, “which suggests that the risk of anovulation was independent of the sugar content included in many flavored yogurt products.” We don’t know if this was just a fluke or exactly what the mechanism might be, but if women skip ovulation here and there throughout their lives, might they end up with a larger ovarian reserve of eggs? 
     
    Women are starting to have their first baby later in life. As you can see in the graph below and at 2:02 in my video, there’s been a rise in women having babies when they’re in their late 30s and 40s.

    We used to think that women’s ovarian reserve of eggs stayed relatively stable until a rapid decline at about age 37, but now we know it appears to be more of a gradual loss of eggs over time. The graph below and at 2:22 in my video charts a steady loss starting at peak fertility in one’s 20s.

    This measures “antral follicle count,” which is an ultrasound test where you can count the number of “next batter up” eggs in the ovaries, as you can see below and at 2:31 in my video. It is probably the best reflection of true reproductive age. It’s a measure of ovarian reserve—how many eggs a woman has left.

    What does this have to do with diet? Researchers at Harvard looked at the association of various protein intakes with ovarian antral follicle counts among women having trouble getting pregnant. “Even though diminished ovarian reserve is one of the major causes of female infertility, the process leading to reproductive senescence [deterioration with age] currently is poorly understood. In light of emerging population trends towards delayed pregnancy, the identification of reversible factors (including diet) that affect the individual rates of reproductive decline might be of significant clinical value.”

    The researchers performed ultrasounds on all the women, studied their diets, and concluded that higher intake of dairy protein was associated with lower antral follicle counts—in other words, accelerated ovarian aging. The graph below and at 3:39 in my video shows what counts look like in nonsmokers: Significantly lower ovarian reserve (12.7 antral follicle counts) at the highest dairy intake, which would be like three ounces of cheese a day, compared to the lowest dairy intake (16.9 antral follicle counts).

    What do these numbers mean in terms of biological age? Is 16.9 down to 12.7 really that much of a difference? As you can see below and at 3:58 in my video, when you look at women with really robust ovaries, a follicle count of 16.9 is what you might see in a 36- or 37-year-old, whereas 12.7, which is what you can see in women eating the most dairy, is what you might see in a really fertile 50-year-old. So, we’re talking year’s worth of ovarian aging between the highest and lowest dairy consumers.

    While it wasn’t possible for the researchers to “identify the underlying mechanism linking higher dairy protein intake to lower AFC,” antral follicle count, they had educated guesses. (1) It could be the steroid hormones and growth factors or (2) “the contamination of milk products by pesticides and endocrine disrupting chemicals that may negatively impact” the development of these ovarian follicles and egg competence.

    “Regarding the former [the hormones], studies suggest that commercial milk (derived from both pregnant and non-pregnant animals) contains large amounts of estrogens, progesterone, and other placental hormones that are eventually released into the human food chain, with dairy intake accounting for 60–80% of the estrogens consumed. Dairy estrogens overcome [survive] processing, appear in raw whole cow’s and commercial milk products, are found in substantially higher concentrations with increasing amounts of milk fat, with no apparent difference between organic and conventional dairy products…” Hormones are just naturally in cows’ bodies, so they aren’t just in the ones injected with growth hormones. And, once these bovine hormones are inside the human body, they get converted to estrone and estradiol, the main active human estrogens. Following absorption, bovine steroids may then affect reproductive outcomes.

    The researchers asserted that further studies are needed and that “it is imperative that these findings are reproduced in prospective studies designed to clarify the biology underlying the observed associations. The latter might be crucial given that consumption of another species’ milk by humans is an evolutionary novel dietary behavior that has the potential to alter reproductive parameters and may have long-term adverse health effects.”

    The video I mentioned about the effects of these estrogens and progesterone in men and prepubescent children is The Effects of Hormones in Dairy Milk on Cancer.

    I talk about the effect of dairy estrogen on male fertility in Dairy Estrogen and Male Fertility.

    How else might diet affect fertility? See related posts below. 

    Michael Greger M.D. FACLM

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  • Skip Breakfast to Lose Weight?  | NutritionFacts.org

    Skip Breakfast to Lose Weight?  | NutritionFacts.org

    Breakthroughs in the field of chronobiology—the study of our circadian rhythms—help solve the mystery of the missing morning calories in breakfast studies.

    Where did this whole “breakfast is the most important meal of the day” concept come from? “The Father of Public Relations,” Edward Bernays, infamous for his “Torches of Freedom” campaign to get women to start smoking back in the 1920s, was paid by a bacon company to popularize the emblematic bacon-and-eggs breakfast. The role of public relations, he wrote in his book Propaganda, is the “conscious and intelligent manipulation of the organized habits and opinions of the masses….” Public relations specialists thereby “constitute an invisible government, which is the true ruling power of our country….”

    Breakfast is big business. Powerful corporate interests, such as the cereal lobby, are blamed for “perpetuating myths such as the value of consuming breakfast.” An editorial in The American Journal of Clinical Nutrition urged nutrition scientists to speak truth to power and challenge conventional wisdom when necessary “even when it looks like we are taking away motherhood and apple pie.” “Actually,” the editorial concludes, “reducing the portion size of apple pie might not be a bad idea, either.”

    So, should we “break the feast” and skip breakfast to lose weight? As I discuss in my video Is Skipping Breakfast Better for Weight Loss?, though “the advice to eliminate breakfast will surely pit…nutritional scientists…against the very strong and powerful food industry,” skipping breakfast has been described as “a straightforward and feasible strategy to reduce total daily energy [caloric] intake.” Unfortunately, it doesn’t seem to work.

    Most randomized controlled studies of breakfast skipping found no weight-loss benefit to omitting breakfast. How is that possible if skipping breakfast means skipping calories? The Bath Breakfast Project, a famous series of experiments run not out of a tub, but the University of Bath in the UK, discovered a key to the mystery. Men and women were randomized to either eat breakfast (defined as taking in at least 700 calories before 11:00 am) or fast until noon every day. As you can see in the graph below and at 2:15 in my video, as in other similar trials, the breakfast-eating group ate a little less throughout the rest of the day but still ended up with hundreds of excess daily calories over the breakfast skippers.

    Those who ate breakfast consumed more than 500 more calories a day. Over six weeks, that would add up to more than 20,000 extra calories. Yet, after six weeks, both groups ended up with the same change in body fat, as you can see below and at 2:36 in my video. How could tens of thousands of calories just effectively disappear? 

    If more calories were going in with no change in weight, then there must have been more calories going out. And, indeed, as you can see in the graph below at 2:52 and in my video, the breakfast group was found to spontaneously engage in more light-intensity physical activity in the mornings than the breakfast-skipping group. Light-intensity activities include things like casual walking or light housecleaning, not structured exercise per se, but apparently, enough extra activity to use up the bulk of those excess breakfast calories. There’s a popular misconception that our body goes into energy conservation mode when we skip breakfast by slowing our metabolic rate. However, that does not appear to be true. But, maybe our body does intuitively slow us down in other ways. When we skip breakfast, our bodies just don’t seem to want to move around as much. 

    The extra activity didn’t completely make up for the added calories consumed by the breakfast group, though. We seem to still be missing about a hundred daily calories, suggesting there may be another factor to account for the mystery of the MIA morning calories. Recent breakthroughs in the field of chronobiology—the study of our body’s natural rhythms—have unsettled an even more sacred cow of nutrition dogma: the concept that a calorie is a calorie. It’s not just what we eat, but when we eat. Same number of calories, different weight loss, depending on meal timing.  

    Just to give you a taste: As you can see in the graph below and at 4:11 in my video, the exact same number of calories at breakfast are significantly less fattening than the same number of calories eaten at supper. Mind-blowing!

    A diet with a bigger breakfast causes more weight loss than the same diet with a bigger dinner, as shown below and at 4:23 in my video. Because of our circadian rhythms, morning calories don’t appear to count as much as evening calories. So, maybe breakfast should be the most important meal of the day after all. 

    If you missed my last video, catch up with Flashback Friday: Is Breakfast the Most Important Meal for Weight Loss or Should It Be Skipped?. 

    Did I pique your interest in chronobiology? If so, you’re in luck. See more in the related posts below. 

    For some breakfast inspiration, check out A Better Breakfast and my recipe videos for a vegetable smoothie and a grain bowl from The How Not to Die Cookbook. 

    Michael Greger M.D. FACLM

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  • What the Science Says About Time-Restricted Eating  | NutritionFacts.org

    What the Science Says About Time-Restricted Eating  | NutritionFacts.org

    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. 

    Michael Greger M.D. FACLM

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