Late Night Eating Linked to Weight Gain

A new study in mice suggests that it’s not just how much you eat, but when you eat it, that influences weight gain.

Researchers at Northwestern University wanted to test whether the timing of meals could influence body weight. Many diet books advise would-be weight losers to stop eating after 6 or 7 p.m. However, it’s never been clear if the strategy works as a behavioral change — we tend to overeat in the evenings in front of the television and the computer. Or is there some physiological reason late-night eating adds extra pounds?

To test whether time of feeding alone can affect body weight, the researchers studied two groups of mice who were fed identical diets of food that contained 60 percent fat. Mice are nocturnal, and they typically consume the vast majority of their calories at night and sleep during the day. For the study, half the mice were fed the diet during the daylight hours when they would normally be sleeping — simulating late-night eating in humans. The other half were given the same food on their regular eating schedule.

At the end of the six week study period, mice in both groups had consumed about the same amount of calories and performed the same amount of exercise. However, the mice who ate when they normally would have been sleeping hours posted an average 48 percent increase in body weight. The mice who ate on a regular schedule had an average increase of 20 percent of body weight. The findings will be published in the October issue of the journal Obesity.

Fred Turek, director of the Center for Sleep and Circadian Biology at Northwestern and the study’s senior author, said that human studies are needed to determine if timing of food intake influences body weight, but the study suggests that late-night eating may be worse, in terms of weight gain, than eating during normal waking hours. The findings would be particularly important for shift workers, who are known to be at higher risk for obesity, diabetes and other health problems. But he notes that it’s not just shift workers who are eating late. Most people eat a large percentage of their calories in the evening and continue eating late into the night.

Dr. Turek notes that humans evolved from a situation where they ate and foraged between sunrise and sunset. “After sunset, there were no refrigerators, no food just hanging around,” he said. “You didn’t eat. But today, people eat most of their calories after sunset.”

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Alex Lickerman, M.D. September 3, 2009 · 1:57 pm

An interesting study in animals. As the lead author acknowledges, we need to confirm this in humans. Interesting to speculate why time of day that calories are consumed might affect overal weight gain. Perhaps it affects basal metabolic weight in a negative way, contrasted to how intense exercise (as discussed in the link below) affects it in a postitive way. Perhaps this will eventually become identified as another tool in the armamentarium for weight loss.


I know every body is different, but for me, eating late is hard on my body.

Consuming most of my calories before 6:30 p.m. has, I think, been an important strategy in my weight loss efforts. The weeks I don’t lose much can usually be linked to my eating later into the night and closer to bedtime.

When I do eat by 6:30 p.m., sometimes 7, I feel lighter and more awake. And I don’t feel bloated in the morning.

Again, this is just my experience. I know for someone like my husband, who has always been at a healthy weight, eating closer to bedtime doesn’t seem to affect him; he can sleep fine and doesn’t seem to feel heavy or bloated in the morning.

It sounds like this study only links late-night eating to mice, and hopefully people will read past the headlines. Can we really compare a nocturnal animal to humans?

Assuming it’s true that calories consumed after sunset are more likely to cause weight gain are there any HELPFUL, PRACTICAL suggestions out there for those of us that even though we are not “shift workers” don’t get home from work until after sunset ?

I feel I’m stating the obvious, but wouldn’t the human equivalent to the mouse experiment be waking up and having a large meal at 3am? That’s not the behavioral change we’re talking about. Seems like an espically long stretch to go from this particular experiment to the relevant human problems.

I guess this is a case of conventional wisdom being right. I thought this was more-or-less self-evident.

So, if someone exercises in the evening (as I do), she is not supposed to have any post-workout snack?

I thought another study recently indicated that the timing didn’t matter at all, just the standard calorie consideration. Hmmmmmm.

Time locks on all refrigerators, also, ban late-night take-out.

I haven’t seen the original study — were the two groups of mice getting the same amount of uninterrupted sleep overall?

FROM TPP — Yes, everything was the same. Think of the second set of mice like shift workers — they just reversed their sleep wake hours so they would be awake when the food arrived.

Yes, this has played out in my experience. I never eat after 6pm and the ONE night i did eat most of my calories for the day after 6pm resulted in an astounding 1 pound weight gain over the next two days after holding steady for months.

No person should alter their dietary habits based on a single rodent study. This experiment will need to be reproduced in a human clinical study before anyone else gives it a moment of consideration.

When I sleepwalk, I head straight for the fridge and make a Dagwood, sometimes out of sticks of butter.

I cannot be certain, but disrupting the sleep cycle sounds like its stressful to the animals. Stress=cortisol=weight gain. Just a thought, its entirely likely that the hormonal cocktail present during the sleep cycle is to blame for the increased storage of calories.

also, there are some studies that show that increases in free fatty acids (which occurs after a high fat diet – note the 60% calories from fat in the mice diet) when you sleep is associated with insulin resistance. This acts to “shunt” the calories from muscle (which aren’t working during sleep any way) and thus to storage, aka adipose tissue or fat.

One question is how well muscular calorie demand can overcome that insulin resistance. In other words, the relative effect of high free fatty acid levels during the day. This may be one reason for the difference in weight and cholesterol results in the classic Atkins v the Eco-Atkins diet (the typical Atkins tends to use lots of animal and thus higher fat based intake versus the Eco that uses nuts and soy and thus lower fat intake for the protein sources.)

Just a few months ago, there was a ‘Health Myths Busted’ column in Well that ‘busted’ the late eating ‘myth’. Was that based on a similar study that found different results? I don’t remember the details, but I remember being really happy about it because I eat dinner as late as 9:00 most nights and had worried that it wasn’t healthy.

FROM TPP — This is the first time a causal link has been shown in a controlled setting. All the other data are based on observational studies.

While I’m a partisan of the “eat the bulk of your calories early and work them off during the day” theory, that last paragraph is nonsense. The lack of refrigeration has minimal effect on being able to keep foraged food handy (short-term) for late-night snacking. Almost anything you can forage during the day will remain edible for at least several hours, and some of it will keep for days, even months. (Beef jerky, anyone? Nuts?) Our stone-age ancestors may not have been able to accumulate silos of grain and deep-freeze their hunt, but that doesn’t mean there wasn’t something edible lying around for those middle-of-the-night munchies!

Query whether the issue is night vs. day, staying awake longer (i.e. getting less sleep gives us more time to eat) or number of hours between last meal and sleep. It isn’t clear from the findings as reported here whether that would be a factor. We used to be told one put on weight by eating just before bed and that you should consume the bulk of your calories in the morning, lessening as the day went on, to stay slim.

I found the post! Quoted below:

“5. Night eating makes you fat.


So these don’t actually disagree because this one is kind of vague. I know I eat a healthy number of calories even if my dinner is fairly late, so I guess I won’t worry. I know I avoid eating an evening snack because I don’t get hungry again before bed, which is one of the reasons I eat late in the first place.

“this study in MICE…”. You can stop reading right there. Weight control in humans are either as simple as number of calories consumed vs burned, or else as complicated as biological and psychological factors influencing hunger, satiety, food choice, memory, culture, and so forth. You can be sure it ISN’T as simple as time of day findings in mice! It is not helpful to publish info like this and suggest it has anything to do with human health. –JSt

But did those ancestors who didn’t eat past the daylight hours go to bed right after supper because the cave was dark? It’s the interval between last food at night and bedtime that interests me.

This is interesting to me because I hardly ever eat at night now and I have gradually shed about 20 lbs. without actually dieting. I eat a good breakfast, and occasionally a light lunch, but for “dinner” (or “supper” depending on the area where you live), I usually just have a cup of low-fat yogurt, if that. I don’t know if this is the reason for my modest weight loss, but it does seem to illustrate the study’s findings.

I recently went through the old Really? columns and found this: //

It had me assured that a calorie was a calorie no matter what. And now.. overturned! nothing is absolute in science and research. We try as hard as we can to put out tight data.
But at the end of the day, just stick to moderation.

FROM TPP — A calorie is a calorie — it’s calories in and calories out. But the calorie out portion of the equation varies by how much you exercise, how much you are dieting, how much sleep you’re getting etc. and now, based on this study, the timing of your food intake…

I am a night shift worker. I’m still not sure what this study considers to be normal. Should I be eating like the mouse?

I know from my experience that eating late adds to weight gain. The problem though is that by the time I get home from work, work out, take a shower, it is almost 8pm. Even if I don’t have to cook (I try to cook for about 5 days on Sundays), it is already pretty late to eat, but what choice do we all have?
I can come home and eat, but then I can’t really work out or do yoga with my stomach full.
We are all overworked, and cram our meals into whatever time is available.