Does having late or heavy dinner make you fat?

Question

Of course, taking calories in general tends to make one fat. My question is whether, relatively speaking, having heavy dinner has more probability of making you fat than, say, heavy lunch. And whether late dinner (closer to your sleep, like 9pm) makes you fatter more than 7pm dinner.

Are there any studies confirming the claim that late night eating is linked to obesity?

Answer 1

The majority of our food is actually digested during sleep, so the common argument that "eating late at night is bad because our metabolism [slows or shuts down] during sleep" is incorrect. With that said, there is a correlation between night eating, low self-esteem, reduced daytime hunger, and weight gain among people who are already obese or prone to obesity, however, this correlation does not necessarily imply causation (i.e., the act of eating a late meal does not necessarily provoke these conditions). It may simply be the case that the types of foods that people prefer to eat late at night are less healthy. There is still much debate on the subject, however, many scientists agree that meal frequency, as opposed to time, is one of the best predictors for weight gain. For example, the time between meals is highly correlated to one's waist size. This makes some intuitive sense, since eating more, smaller meals will help regulate insulin levels, and spikes in insulin levels (which can be caused by large meals and/or large gaps in time between meals) have been linked to weight gain.

I remember hearing on NPR a year or two ago about a study which specifically tried to test the claim that eating late at night is unhealthy. The study concluded that there was absolutely no correlation between the proximity of mealtime to sleep and weight gain, other than the fact that people tend to choose to eat more unhealthy foods late at night. I can't seem to find a reference to that study, however.

Update: A newer study followed the eating and sleeping patterns of 52 subjects over one week. They found a correlation between "late sleepers" (i.e., people who go to sleep late and wake up late) and high body mass index, and that eating after 8pm was associated with higher body mass index. A New York Times article summarizing the results of the study makes the further claim that eating late at night leads to weight gain, however, I disagree with that claim on the grounds that correlation does not imply causation. In fact, that study noted:

Late sleepers consumed more calories at dinner and after 8:00 PM, had higher fast food, full-calorie soda and lower fruit and vegetable consumption.

Therefore, I think the results of the study can be interpreted to mean that there is a correlation between eating/sleeping late and a poor diet.

Furthermore back in 2006, the same research team conducted a study on monkeys in which they were fed a diet similar to the average (i.e., high-fat) diet common in the USA. The only variable was the time of day that the monkeys were fed. With all else remaining constant, the researchers found no correlation between weight gain and time of feeding.

It was really interesting to see that the monkeys who ate most of their food at night were no more likely to gain weight than monkeys who rarely ate at night. This suggests that calories cause weight gain no matter when you eat them.

Answer 2

A few months ago I saw this video on Youtube http://www.youtube.com/watch?v=mNYlIcXynwE which I found to be a useful explanation of how we make fat.

The central point that I got from it was that it doesn't matter as much when you eat, but it does matter if you eat too much in any given time-window. Overeating overwhelms the 'convert food energy to fuel' receptors which instead stores it as fat.

So on the biological level, it isn't the hour of the day, but the amount of food in any given sitting.

Answer 3

I am going to respectfully disagree with ESultanik here. I didn't pay to read the study, but I suspect that the reason they make that claim is that the body isn't expending energy for other things (like walking and working out and doing laundry) so it has more energy to devote to digestion at that particular time. That doesn't mean that "the majority of our food is digested during sleep", only that digestion appears to be sped up during sleep because it's not doing other things.

But that's a red herring.

There is one, and only one, thing that causes one to be fat: eating more calories than what is used up by the body.

All the other variables like portion size, ratio of protein to fat to carbs, when you eat, whether or not you eat after a workout or before bed, whether or not you exercise, are variables that may determine how many calories your body is using and receiving at any given moment, but the basic equation remains the same: A meal at 10pm has the exact same number of calories that the same meal at 11am would have. If you do the same daily routine twice a week and only change when you eat your heavy meals, there would be no change in your body because you haven't changed either your calorie intake or output.