Recent studies have suggested that eating late at night may lead to weight gain, so how late is too late to eat? And while we’re asking questions, do we really know that you’ll gain weight if you eat a late dinner?
Why is everybody talking about late meals?
If you’ve seen this question pop up a lot recently, it’s because of a study that investigated what happens in volunteers’ bodies when they are made to eat the same three meals early in the day (breakfast, lunch, and dinner) or late in the day (lunch, dinner, and another evening meal). The researchers say they found that the late eaters were more hungry, burned fewer calories, and that their fat cells expressed genes that have been linked to fat gain.
It’s important to note that this study did not test whether people actually gained or lost weight. You read that right: Despite all the headlines saying that eating late is “bad for you” or “bad for weight loss” or “raises obesity risk” or is “something you should absolutely avoid,” the study didn’t actually track participants’ weight. In fact, the authors write:
Note that the present study aimed to test the acute [i.e., short-term] effects of late eating on energy balance regulation, and not whether long-term adherence to such a schedule would result in weight gain over time, or whether the body would adapt allostatically.
In other words, it’s entirely possible that your body would adapt to the new eating schedule if that’s the way you actually lived your life. (The participants in the study only ate on the assigned schedule for six days at a time.)
What does other research say about late meals?
There is other research suggesting that late meals may make it easier to gain weight, but it’s not as simple as changing mealtimes to change the size of your body.
For example, there are mouse studies showing that when mice are made to eat during the day (when they would normally be asleep), they gain weight faster than mice who are fed at night. This research doesn’t apply neatly to humans, though, for several reasons. For one, the mice are usually young and growing, which may not represent what happens during adulthood; for another, they are mice and not humans. (Small detail, I know, but worth pointing out.)
Healthline has a good roundup here of the human research to date. Much of it disagrees with the idea that late meals make you gain weight: For example, there are plenty of studies that find timing doesn’t make much of a difference when calories are equal. Which makes a lot of sense when you think about it.
What you eat is more important than when you eat it
The idea that late meals may affect weight gain has been around a long time, and it’s mutated into a handful of myths that bear no relationship to the science. For example, it’s a myth that your body “doesn’t burn” calories you eat late at night. Your body burns calories all the time, including while you sleep. In fact, most of your calorie burn happens when you’re resting.
The science on late-night eating has found that people who eat late tend to eat more calories than those who eat early, and that they’re more likely to eat processed, high-calorie foods. The new study mentioned above found that subjects were hungrier if they were in the group that ate their meals late, which tracks.
But, again, there are probably other things going on here. If you eat late, it’s probably because you’re up late studying or because you work the night shift. In those cases, you might not have the time, energy, or resources to cook yourself a healthy meal. You’ll have chips and soda, or you’ll order from that pizza place that’s open late. It’s also possible that working nights is one of the factors that’s messing up your circadian rhythm; the late meals might be an effect rather than a cause. Not getting enough sleep has been linked to weight gain.
If we look again at the recent study, the people who ate late meals had approximately a 5% reduction in the number of calories their bodies burned, although this was an average and not true for everybody—some people burned slightly more calories on the later diet. Five percent works out to be about 115 calories if you eat 2,300 calories per day (the average for American adults). That’s equivalent to one banana, or a one-ounce slice of cheese. Even if this effect continued beyond the six-day research study, you could combat it by eating the equivalent of one fewer ounce of cheese per day.
For similar reasons, the Winchester Hospital recommends eating earlier in the day if you can—but they also say: “if you miss a healthful dinner at 6:00 [p.m.], there’s no reason not to eat it at 9:00!”
Late meals may influence sleep
Personally, I try to avoid eating too late, but not for reasons related to weight gain. It’s really just that I expect that my sleep won’t be as good when I eat shortly before bed. (I also find that I eat better, overall, when I eat earlier in the day. That’s because I’ve probably planned my meals, rather than waiting until it’s almost bedtime, realizing how tired I am, and then eating whatever food I can find in the kitchen that I can prepare quickly.)
This is the standard advice that you’ll get from sleep wearable companies like Whoop. But science doesn’t always agree. The study we mentioned above found that participants slept equally well in both groups, and other research like this finds that late dinners may actually be better for sleep (in that last study, people who ate a late dinner had more deep sleep in the beginning of the night).
If you’re concerned about late meals affecting your sleep, try eating earlier and see if you get a better night’s sleep afterward (for example, by taking notes on how rested you feel the next morning). Then adjust accordingly.
So how late is late?
OK, so what if you want to try eating your meals earlier in the day? After all, it may be worth a try, even if it’s unlikely to be a magic bullet for weight loss.
In the study we discussed at the beginning of this article, the late meal was eaten two and a half hours before bedtime (so, at 8:30 p.m. if you go to bed at 11). The people who ate the early meals had their dinner about four hours earlier—or, in this example, 4:30 p.m.
Meanwhile, there is a form of intermittent fasting that’s been suggested to be better for aligning our bodies’ circadian rhythm. While it doesn’t have a ton of research behind it, it’s worth noting that it typically has adherents eat between 8 a.m. and 6 p.m.
Advice about avoiding late meals generally falls within these timeframes. For example, Oura (another sleep wearable) recommends having your last big meal at least three hours before going to bed, or about 8 p.m. at the very latest if you go to bed at 11. Meanwhile, if you want to avoid a heartburn flare-up, medical sources usually advise finishing your last meal at least three hours before bed; some say four.
Considering all of those factors—and again using the example of an 11 p.m. bedtime—you may want to eat dinner no later than 7 p.m. to make sure you’ll be done by 8 p.m. and that your stomach will be empty or close to it by bedtime. If you do need to eat later, though, just be extra mindful of your choices and eat the same meal you would have at a regular dinnertime—even if it means prepping yourself a healthy meal earlier in the day so that you aren’t tempted to order out.
