Although there has been some evidence to the contrary, scientists generally believe that late-night eating can cause significantly more weight gain than eating during the day time.
The reasons for this aren’t entirely clear, but it may have to do with circadian rhythms. A new study (see abstract) finds strong evidence that this is the case, and suggests that eating outside of “normal” times such as late at night can be very bad for your waistline.
Scientists at Northwestern University worked with mice, and most mice are nocturnal, meaning they are most active from dusk until dawn. So their circadian rhythms are entrained such that their normal sleeping hours are during daylight.
Over six weeks one group of mice was allowed to eat as much of a high-fat diet as they desired during normal, 12-hour feeding phase. The other group was allowed to eat as much as they wanted during the daytime, or the time when that group of mice normally slept.
Both groups ate the same amount of food, 20 percent more than normal, and there was no difference in their exercise amounts.
The effect of light or dark phase feeding on body weight.
What happened is really surprising. The group that ate during its normal wakeful hours had a 20 percent gain in weight, as you would expect from consuming 20 percent more food. However, the group that consumed a high-fat diet during its normal sleeping hours gained 48 percent more weight.
That’s 1.5 times as much weight as the group that ate during their normal wakeful hours. Think about that the next time you’re up late and get the munchies.
The findings, published in the journal Obesity, are a step toward understanding of how meal timing and the body’s circadian rhythm regulate energy and in turn weight gain in humans. They also suggest that it is indeed a very bad thing to eat late at night, even if you’re counting calories.