Health Library

True or False: Eating at Night Will Make You Gain Weight

mythbuster graphic Eat late, gain weight? This myth has been around for years, and although some people could swear that their late-night eating habits do make them gain weight, recent research has shown that your body doesn’t process food differently at different times of the day. The total amount of calories that you take in, and how much you exercise during the day, are what affect your weight. However, many people do tend to overeat and choose high-calorie foods as snacks at night, both of which will cause weight gain.

Evidence Against the Health Claim

A study by scientists at Oregon Health and Science University examined the eating habits and weight-gain patterns of rhesus monkeys, which they considered to be a useful model for studying human obesity . The study found that the monkeys who ate most of their food at night were at no greater risk for gaining weight than those who chose to eat earlier in the day. Such evidence supports the claims of many health professionals and organizations, including the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), that it’s the amount of calories you take in, not the time of day you consume them, that affects the amount of weight gained or lost.

Under normal circumstances weight fluctuates over weeks and months—not hours—due to long-term patterns of eating and exercise. Although your metabolism does slow down at night, you are still using energy for basic bodily functions, and thus are still burning calories when you sleep. And many people are also quite sedentary during the day. Your body will not store more fat after eating the same meal at 9:00 pm as opposed to 6:00 pm—the calorie intake is the same. If you overeat, your body will store the extra calories as fat no matter what time you consume them.

Evidence for the Health Claim

Although research has yet to show that the time of day you eat influences the amount of weight you gain or lose, many peoples’ late-night eating patterns result in the consumption of extra calories and subsequent weight gain. Late-night snackers often eat when they do not because they are actually hungry, but out of habit, or because they are bored, tired, or stressed. Furthermore, late-night snacks are often unhealthy—calories from munching on chips, cookies, chocolate, pizza, and ice cream add up quickly. Even when people eat late meals rather than snacks, they may be very hungry because lunch was so long ago, and so they naturally opt for larger portion sizes. Finally, calorie-dense “fast food” is far more appealing than preparing a well-balanced, healthier meal when you’re tired and just want to relax in front of the television.

Various techniques have been suggested to limit total daily calorie intake. Starting the day with breakfast will jumpstart your metabolism and may also help you make better food choices throughout the day because you won’t be as hungry. Because many of your “extra” calories are consumed late at night when you don’t really need them, eating protein and fiber for dinner may make you feel full and curb your late-night hunger. The NIDDK suggests avoiding snacking while your mind is on other tasks, and instead tuning into your meals by eating in the dining room or at the kitchen table. It is easy to lose track of how much you are eating if you are distracted by the television or computer. Also, before you grab a bedtime snack, think about how much you have eaten and exercised that day, and consider if it is really necessary.

Some health experts do suggest not eating after a certain hour of day, but this is not because your body processes food differently at night. Instead, setting a time beyond which you will not eat reduces the likelihood of snacking on calorie-laden foods, which in turn reduces your total calorie input for the day.


This is a tricky one—technically, the time of day you eat doesn’t affect how your body processes food. What matters is your total calorie intake and how much you exercise during the day. However, people who eat late at night tend to choose high-calorie foods that their bodies can do without. If you are one of these people, avoiding food after dinner may help you deter weight gain—or even promote weight loss. But, if you miss a healthful dinner at 6:00, there’s no reason not to eat it at 9:00!


Eating at night myth exploded. BBC News website. Available at: . Published November 2003. Accessed November 6, 2008.

Eating at night = weight gain: Myth or fact? Columbia University, Go Ask Alice website. Available at: . Updated June 2007. Accessed November 6, 2008.

OHSU scientists dispel late-night eating/weight gain myth. Oregon Health and Science University website. Available at: . Published February 2006. Accessed November 6, 2008.

Scientists dispel late-night eating/weight gain myth. ScienceDaily website. Available at: . Published February 2006. Accessed November 6, 2008.

Weight-loss nutrition myths. Weight-Control Information Network website. Available at: . Accessed November 6, 2008.

Wyatt HR, Grunwald GK, Mosca CL, Klem ML, Wing RR, Hill JO. Long-term weight loss and breakfast in subjects in the national weight control registry. Obesity Research . 2002;10:78-82.

Image Credit: Nucleus Communications, Inc.