The 8-Hour Diet: The Best Time to Eat to Trick Your Body Into Losing Weight

Thursday May 7 | BY |
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businessman in suit in front of city- background is eating and looking for time
Recent studies suggest it’s not how much we eat, necessarily, but when we eat it that could be contributing to weight gain and disease.

Weakest time of day for me, when it comes to sticking to a healthy diet?

After 9 at night, easy.

The night munchy monster is my nemesis. I’ve always been a night owl, and seem to get a second wind around 10:00 to 10:30, after which I may churn out a new blog, edit a chapter in my next novel, do some research, or simply read a new book I’m into.

And without fail, during that time, my stomach turns and twists and flips over on itself screaming at my brain about how hollow and empty it is.

It’s like The Little Shop of Horrors—“Feeeeed me!”

I know if I give in, I’ll be sorry. Eating after 10 is the fastest way for me to put on an extra pound or two. I can indulge myself before that (within reason), but after? Forget it.

Turns out I may not be the only one quite severely affected by when I choose to eat. Recent studies have found that limiting our consumption to only certain hours of the day can not only help us maintain a healthy weight, but may have other health benefits too, such as protecting cardiovascular health, limiting inflammation, improving blood sugar, and more.

Some say that by limiting the hours in which you allow yourself to eat, you can lose weight without restricting your calories.

(Authors David Zinczenko and Peter Moore talk about this in depth in The 8-Hour Diet.)


Recent Study Suggests Limiting Eating Time to 12-Hour Periods

Our most recent study on this was published just this last March (2015). Researchers from San Diego State University restricted the time span during which fruit flies could eat. They split the flies into two groups: 1) the first were given a standard diet and allowed to feed all day long, 2) and the second was allowed access to food only 12 hours a day.

Researchers then put the flies through a barrage of tests concerning their sleep habits, body weight, and heart physiology. (Scientists have long used fruit flies for these types of experiments, so they know how to test all these things!)

Results showed that the flies on the restricted feeding schedule experienced a number of health benefits:

  • They slept better
  • They didn’t gain as much weight as the other group
  • They had far healthier hearts than the other group, even though they ate similar amounts of food

The flies in the restricted group were so much healthier the researchers thought for a moment they had mistaken some in a younger group for the older ones in the study. “We had to repeat the experiments several times to become convinced that this improvement was truly due to the time-restricted eating,” said Shubhroz Gill, lead author of the study.

Still, fruit flies aren’t humans. What about other studies?

Animal Studies Show Time-Restricted Eating Keeps Weight Gain at Bay

Scientists have been investigating the idea of restricting eating time for a while now. Here are a few of the animal studies we have showing it can be beneficial:

  • 2012: Researchers restricted the feeding times of one group of mice to eight hours a day, and allowed a second group to eat whenever they wanted to. They found both groups ate the same amount of calories, but those that ate all the time were more likely to become overweight and showed symptoms of diabetes. Those on the restricted diet gained little weight and had no metabolic problems.
  • 2014: Researchers split mice into four groups based on the type of diet they were fed: 1) high-fat, 2) high-fructose, 3) high-fat and high-fructose, and 4) regular mouse diet. Some were allowed to eat whenever they wanted to, and others were restricted to periods of 9, 12, or 15 hours. Caloric intake of all mice was the same. After 38 weeks, results showed that those mice that could eat whenever they wanted to were generally obese with metabolic problems, whereas the restricted mice remained slim and healthy, even if they were allowed to eat all they wanted sometimes on the weekends. Even obese mice that were put on the time-restricted diet lost weight, reduced blood sugar levels, and had lower cholesterol levels.

Both of these studies seem to suggest that as long as we eat only during a specific 8-12 hour time frame, and refrain from eating during the other 12-plus hours, we can lose weight and experience better health even if we don’t restrict calories—and that we can even cheat on the weekends without seeing disastrous setbacks.

Easy take-away—put more time in between dinner and breakfast, and don’t eat during that time!

Shift-Work Throws Blood Sugar Out of Whack

Do we have any human studies confirming these results?

In April of this year (2015), Harvard University reported on a new study of 14 humans, conducted by researchers from Harvard-affiliated Brigham and Women’s Hospital. It was a small study, but it had some interesting results.

First, the researchers had the participants eat their first meal of the day at 8:00 a.m., and their last meal at 8:00 p.m. They then slept at night. Then, during a second time period, they had the participants eat breakfast at night (8:00 p.m.) and dinner at 8:00 a.m., and had them sleep during the day (as might be the case during shift work).

The meals in both cases were the same. Researchers tested glucose levels, insulin, and other hormones at 10-minute intervals after each meal and hourly. Results showed the following:

  • Those who ate breakfast at night had glucose levels 17 percent higher than those who ate it in the morning.
  • Simulated night work (sleeping during the day) resulted in lowered glucose tolerance for multiple days.

In other words, the shift-work diet seemed to throw blood sugar control out of whack, putting those participants at risk of diabetes, even though they ate the same thing and the same number of calories as the regular-schedule participants.

Nighttime Eating the Worst

Most of our human studies on time-restricted eating to date concern eating at night. From what we know so far, this is the worst time to eat. (Ugh.)

  1. Eating late leads to weight gain: Researchers followed about 200 subjects, some of which were nighttime eaters (people who ate between the hours of 11:00 p.m. and 5:00 a.m.). They found that nighttime eaters gained more weight than did non-nighttime eaters, even though both groups ate about the same number of calories.
  2. Eating late leads to overweight and binge eating: A 2007 study on over 400 human participants found that “night eating syndrome (NES),” defined as consuming most of one’s food in the evening and night, was associated with a higher body mass index (BMI), binge eating, and depression.
  3. Eating late could be bad for your brain: In a 2015 study, researchers allowed one group to eat when they normally would, but the other group could eat only during their normal sleep times. All ate the same amount of calories and slept the same amount of hours (just at different times). After a few weeks, results showed that late-night eating disrupted learning and memory.
  4. Eating and sleeping late could pack on the pounds: In 2011, researchers tested 52 volunteers, about half of which were normal sleepers and the other roughly half which were late sleepers. Late sleepers slept for fewer hours, got to sleep later at night, and ate more calories after 8:00 p.m. No surprise—late sleepers/eaters had higher body mass indexes (BMIs). Researchers noted that their analysis showed that eating after 8:00 p.m. could increase risk of obesity, regardless of sleep times.
  5. Fasting at night lowers risk of breast cancer: A very recent human study of over 2,000 women found that for every three hours of extra fasting at night, women were 20 percent less likely to have high blood sugar—a known risk factor for breast cancer and diabetes. “Increasing the duration of overnight fasting could be a novel strategy to reduce the risk of developing breast cancer,” said lead author Catherine Marinac.
  6. (Previous studies have linked diabetes to a higher risk of breast cancer.)

  7. Eating less at dinner can improve blood sugar levels in those with diabetes: In a study published in 2014, researchers found that when patients with type 2 diabetes were given a “high-energy” breakfast and a “low-energy” dinner—as opposed to another group eating the same amount of calories in six small meals throughout the day—they lost body fat and improved insulin sensitivity.
  8. Eating lunch a little earlier could help you fit into your clothes: In a 2013 study, researchers followed about 420 humans for 20 weeks. They separated them into two groups depending on when they ate lunch. “Early eaters” ate lunch before 3:00 p.m., and “late eaters” ate lunch after 3:00 p.m. Results showed that late lunch eaters lost less weight and lost it more slowly than those who ate lunch earlier. Calorie intake and sleep duration was similar in both groups.

There are some studies that have found conflicting results. A study on 16 monkeys, for example, published in 2006, found that those who ate most of their food at night were no more likely to gain weight than monkeys that rarely ate at night. Still, these were monkeys—I’m picturing much more active little critters than many of us humans are?

Why Does Time-Restricted Eating Work?

Why would when we eat have such an impact on our weight and our health?

Scientists aren’t yet sure, but they have theorized that constant eating—as is common in today’s culture—deprives our bodies of time to rest, recuperate, and perform needed maintenance. Instead, we’re constantly stressing the liver, elevating blood sugar levels, and taxing our systems.

On the other hand, when we stop eating for several hours, the liver gets a chance to repair cellular damage, break down cholesterol into acids, and break down fat.

Plus, it may be that the body is just better at processing and metabolizing food during the day, when it’s used to doing so. Late-night calories can impact sleep cycles, throw off the normal body rhythm, and send the body to work digesting when it’s been working all day and is ready to rest. Add to that the fact that we tend to be much less active at night and it’s easy to see that all those calories have nothing to do but flow into our bellies.

It all comes down to the daily sleep/wake cycle that we’ve evolved with, that in today’s world, is often disrupted. With our ability to turn on the lights at most any time of day or night (see our post on how lights can affect our health), our obsession with using bright gadgets at all hours of the day and night, and our tendency to always be eating something whatever we’re doing, we’re failing to give our bodies the time they need to rest and recover.

Researchers have noted in several of these studies that our natural circadian rhythms expect we’ll be eating, exercising, and sleeping at certain times, and that it carries out a number of restorative processes in the evening when we’re supposed to be laying off the food. Eating sends signals to our body clocks, and eating at later times can throw those clocks out of sync, making the body less efficient at processing that food.

“When the timing of meals do not match the sleep-wake cycle well,” said study author Frank Sheer of Brigham and Women’s Hospital, “there’s a disconnect between the different clocks that we have in basically all the cells of our body.”

In a 2013 study of 93 women, for example, researchers noted that those who eat their largest meal for breakfast are more likely to lose weight (an average of 18 pounds) and waist line circumference (an average of three inches) after 12 weeks than those who eat a large dinner. They also had lower levels of insulin, glucose, and triglycerides in their blood throughout the day.

Lead author Daniela Jakubowicz noted that the time of day that we eat can have a big impact on how the body processes food, because metabolism is impacted by circadian rhythms.

“Forget all the standard advice about cutting calories,” say the authors of The 8-Hour Diet. “Forget willpower, forget diet aids, forget counting calories, forget the glycemic index. Forget everything you have ever heard about weight loss, and instead, just do this: Eat whatever you want, as much as you want. But only eat during an 8-hour period each day (with a few cheats thrown in here and there!).”

If you try it, let us know if it works for you!

Do you struggle with late-night eating, or do you munch around the clock? Have you found a solution? Please share your tips with our readers.

* * *

Shubhroz Gill, et al., “Time-restricted feeding attentuates age-related cardiac decline in Drosophila,” Science, March 13, 2015; 347(6227):1265-1269,

Megumi Haton, et al., “Time-Restricted Feeding without Reducing Caloric Intake Prevents Metabolic Diseases in Mice Fed a High-Fat Diet,” Cell, June 6, 2012; 15(6):848-860,

Amandine Chaix, et al., “Time-Restricted Feeding is a Preventative and Therapeutic Intervention Against Diverse Nutritional Challenges,” Cell, December 2, 2014; 20(6):991-1005,

Gretchen Reynolds, “A 12-Hour Window for a Healthy Weight,” New York Times, January 15, 2015,

Haley Bridger, “You are when you eat,” Harvard Gazette, April 13, 2015,

Marci E. Gluck, et al., “Nighttime eating: commonly observed and related to weight gain in an inpatient food intake study,” AM J Clin Nutr, October 2008; 88(4): 900-905,

A. Pawlowski, “Why eating late at night may be bad for your brain,” Today, February 22, 2015,

Colles SL, et al., “Night eating syndrome and nocturnal snacking: association with obesity, binge eating and psychological distress,” Int J Obes (Lond). November 2007; 31(11):1722-30,

Oregon Health & Science University, “Scientists Dispel Late-Night Eating/Weight Gain Myth,” ScienceDaily, February 2, 2006,

Baron KG, et al., “Role of sleep timing in caloric intake and BMI,” Obesity, July 2011; 19(7):1374-81,

“Extended Overnight Fasting May Lead to Reduced Breast Cancer Risk,” American Association for Cancer Research, April 20, 2015,

Daniela Jakubowicz, et al., “High-energy breakfast with low-energy dinner decreases overall daily hyperglycaemia in type 2 diabetic patients: a randomised clinical trial,” Diabetologia, 2015; DOI: 10:1007/s00125-015-3524-9,

Daniela Jakubowicz, et al., “High Caloric intake at breakfast vs. dinner differentially influences weight loss of overweight and obese women,” Obesity, December 2013; 21(12):2504-2512,;jsessionid=733590476008911CC6A0460DCD092534.f03t01.

“Study explains what triggers those late-night snack cravings,” OHSU, [Press Release], April 29, 2013,

M. Garaulet, et al., “Timing of food intake predicts weight loss effectiveness,” International Journal of Obesity, 2013; 37:604-611,

Allison Aubrey, “To Maximize Weight Loss, Eat Early in the Day, Not Late,” NPR, January 30, 2013,

Colleen M. Story

Colleen M. Story

Colleen M. Story, a northwest-based writer, editor, and ghostwriter, has been creating non-fiction materials for individuals, corporations, and commercial magazines for over 17 years. She specializes in the health and wellness field, where she writes and ghostwrites books, e-books, blogs, magazine articles, and more.

Colleen is the founder of Writing and Wellness. Her fantasy novel, “Rise of the Sidenah,” was released with Jupiter Gardens Press in September 2015. Her literary novel, “Loreena’s Gift,” is forthcoming in spring 2016 from Dzanc Books. She lives in Idaho.


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  1. Dennis says:

    30+ years ago I created an eating system for myself. I never recommended it because according to all of the experts, it was not healthy. I found out a year ago and verified somewhat in your article, that I may have been on to something, although I sometimes, still do eat later than is best.

    1] I eat 1 meal a day [sometimes a very healthy meal, sometimes a very UNhealthy meal].

    2] I eat at 7pm or 8pm [finishing at 8 or 9]

    3] Go to sleep about 1 am [I’m a late-night person]

    4] About 12 noon the next day, I make a smoothie of about 10 – 12 of the most nutritious dense superfoods the Earth has to offer.

    So I allow my body 15 – 16 hours to digest my food and rest my organs and 6 – 7 hours for my body to utilize most effectively, the super nutrition I give it at 12 n.

  2. BEWARE.

    I’m been doing this for a while. It does work. It’s usually called an “eating window”. E.g. an “8 hour eating window”

    BUT –

    It creates an adrenal response. Especially when you first try it, so start slowly and build up to smaller windows.

    The adrenal response is more pronounced in people who are stressed or have allergies. For this reason is would be better to sort these problems out first.

    If you got right at it as I did. It can seem like it is working but that is the adrenalin. And after a few days your energy can drop due to overload. This is why it is best to start slowly and be careful.

  3. zirah1 says:

    Good article. I’ve heard about limiting your eating hrs before, but usually in the context of giving your digestive system a rest, not as a way for losing weight. Thanks for all the info.

  4. Kym says:

    It’s an interesting concept, though not a new one. Paul Nison’s Daylight Diet, Brad Pilon’s Eat, Stop, Eat or even Martin Berkhan’s Lean gains all spring to mind. I also become very concerned when I see “forget the glycemic index” and especially “eat whatever you want, as much as you want.” There is far more to being healthy than losing weight and many of these factors only emerge over the longer term.

    I do appreciate the many studies referenced in this article, though. I know firsthand how time-consuming that is. In that respect, this is an excellent resource. Many thanks.

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