Late Night Eating And Weight Gain

The right diet, a good cardiovascular exercise program and a full body resistance training program form the foundation of any weight loss strategy. However, other lifestyle choices can have a big impact on weight loss success. An example of one such lifestyle choice is to limit eating after 8:00 PM. This has been recommended to dieters for generations, but is there any research to back this up? Do people who eat a lot of food after 8:00 PM really gain more weight? In this post, we’ll take a look at what the research tells us.

I find this topic interesting for a couple of reasons. First of all, when I was in high school and college, I could not gain weight for the life of me. I ate all the time, but I had a really high metabolism and was extremely physically active, so I burned off every calorie I put into my body. This probably sounds like heaven to people who were struggling with their weight, but it wasn’t so great. I was really, really skinny.

One of my fraternity brothers told me that to gain weight, I just had to eat 2 peanut butter and jelly sandwiches right before I went to bed. I told him that those few hundred calories wouldn’t make a difference because I was already eating a ton of calories all day. He said it wasn’t just the extra calories, it was when I was eating them that was so important. I gave it a shot. The summer between freshman and sophomore year in college, I ate 2 peanut butter and jelly sandwiches right before I went to bed. I was also working in construction and lifting weights. I put on 30 lbs. in 4 months!

When I became a licensed nutritionist and started working with weight loss clients, I found that a lot of people who were overweight ate a high percentage of their food at night. Having them stop this habit, in addition to changes in diet and exercise, helped them to lose weight. I also noticed that clients that made good progress with their diet and exercise but did not stop eating late at night did not lose much weight at all. I have been recommending to limit late night eating to my weight loss clients for over 15 years.  So what does the research have to say about this?

The Research

Surprisingly, I did not find much high quality research on the topic of late night eating and weight gain. However, I did find several investigations utilizing weaker study designs that hint at a potential association.

1) In a recent cross-sectional investigation published in the American Journal of Clinical Nutrition, 110 college-aged men and women recorded all of their food intake with a time stamp so that the hour of consumption could be accurately recorded. When compared to normal weight subjects, overweight subjects consumed significantly more of their calories 1 hour closer to melatonin onset, which was around 11 PM (Reference 1).

2) Another cross-sectional investigation published in the journal Appetite showed that protein, fat and carbohydrate consumed after 8:00 PM were associated with a higher BMI in a group of 52 volunteers that filled out 7 day food logs (Reference 2).

3) This investigation is a much older study that only had an abstract. I include it here because it is interesting and I have never seen results like this before. In this study, 9 young men were given the same meal at 9:00 AM, 5:00 PM and 1:00 AM (Reference 3). Energy expenditure was measured by indirect calorimetry for one hour before, and six hours after consumption. Dietary induced thermogenesis (DIT) of the meal was calculated as the 3 hours of energy expenditure above basal metabolic rate.

Morning DIT was significantly higher than afternoon DIT (P=.04) and night DIT (P=.0002). Afternoon DIT was higher than night DIT (P=.06). What this means is that these young men burned a higher percentage of their meal’s calories in the morning than they did in the afternoon or at night.

Conclusions And Recommendations

The research on late night eating and weight gain is largely unimpressive. To come to a firm conclusion, you’d really want to see a number of randomized trials and well-designed cohort studies showing an association with late night eating and weight gain. To my knowledge, these studies have yet to be conducted. 

What we are left with are cross-sectional studies that are a much weaker form of evidence. Having said that, several studies I did find suggest a cross-sectional association between eating late at night and gaining weight. One study was a trial that mentions a potential mechanism, but it is so old I could not find the full text to properly evaluate it.

I would say the evidence, while weak, is suggestive of a relationship between late night eating and weight gain. So what are some potential mechanisms at play here?

1) Eating food late at night simply adds extra calories that you would not consume otherwise. 

2) Food consumed late at night is of poor nutritional quality and more likely to cause weight gain. Most people snack on high glycemic carbs like chips, pretzels and dessert late at night. These calories spike the blood sugar and increase fat storage.

3) Another hypothesis is that our metabolism slows down quite a bit at night, so more of what we consume is stored as fat.

4) The thermic effect of food is lower at night, so more of what we eat is stored as fat.

Despite the weak forms of evidence and uncertain mechanisms, I still think it is a good idea to limit eating after 8:00 PM if weight loss is your goal. I have seen this be a very big part of the equation for many weight loss clients over the years.

References

1) McHill AW, et al. Later circadian timing of food intake is associated with increased body fat. American Journal of Clinical Nutrition 2017; 106:1213-19.

2) Baron KG, et al. Contribution of evening macronutrient intake to total caloric intake and body mass index. Appetite 2013; 60:246-51.

3) Romon M, et al. Circadian variation of dietary induced thermogenesis. American Journal of Clinical Nutrition 1993; 57:476-480.