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Timing Is Everything: New Research Says Late-Night Eating Increases Weight Gain

By L. K. Regan

Every body-conscious gay man has heard the adage "calories in, calories out." Heck, some of us have it tattooed somewhere on our body! But two studies in the last couple of months have put new doubt to that notion. In short, it may not only matter what you eat, but when you eat it.

Both studies, one published in June of this year, the other earlier this month, seek to solve the conundrum of shift workers, who are typically heavier than day-scheduled workers despite reporting no real difference in diet. The first study, presented at the 23rd Annual Meeting of the Associated Professional Sleep Societies in June, surveyed a group of sleep-restricted subjects who were given free access to as much food as they liked. The researchers found that, despite reporting reductions in appetite, cravings, and food consumption, the subjects nonetheless gained weight over the course of the study. According to lead investigator Dr. Siobhan Banks, a research fellow at the University of South Australia and former assistant research professor at the University of Pennsylvania School of Medicine, the combination of a laboratory setting and the extra time for snacking provided by sleep deprivation may have led to more eating than the subjects were aware of. As Dr. Banks told the conference, "During real-world periods of sleep restriction (say during shift work), people should plan their calorie intake over the time they will be awake, eating small, healthy meals. Additionally, healthy low fat/sugar snacks should be available so the temptation to eat comfort foods is reduced. Finally, keeping up regular exercise is just as important as what food you eat, so even though people may feel tired, exercising will help regulate energy intake balance."

That sounds manageable, but a second study, conducted at Northwestern University and published in the September 3 online journal Obesity, seems to imply that the problem is not that we eat more than we think—it's that late-night calories are actually processed differently than daytime ones. The Northwestern team found that in mice, eating at irregular times (the equivalent of the middle of the night for humans) caused weight gain. Though its subjects were rodents as opposed to humans, this study is the first proof of a causal relation between meal time and weight gain. For this study, mice were divided into two groups, and given as much high-fat food as they wanted during a 12-hour feeding period. The only difference: one group had those 12 eating hours during their normal wakeful time of day, and the other group had them while they would ordinarily be asleep. Result: the group that had to eat when their bodies would typically want to sleep gained 48 percent over their original weight, while the other mice, despite the same caloric intake and activity level, gained only 20 percent.

In both studies, the experimental models give some pause. In the first case, spending a few wakeful nights in a sleep laboratory is hardly the same as consistently working and eating at night. In the second case, leaving aside the question of the applicability of rodent studies to humans, these mice were suddenly offered a very high-fat diet—leaving open the question of whether ordinary caloric intake would cause the same effect. In general, one major question is the applicability of this research to people who may not be shift workers but who, as for so many of us, can't get dinner on the table before 9 PM. Is a late evening meal or snack really the same for our bodies as a full four AM meal? This research is a new effort at finding an answer to exactly that question.

Still, the researchers think that their results indicate the basic role of circadian rhythms in the body's fuel consumption—and storage. Says Fred Turek, a professor of neurobiology and physiology at Northwestern who was lead author on the second study, "We think some factors are under circadian control. Better timing of meals, which would require a change in behavior, could be a critical element in slowing the ever-increasing incidence of obesity." In other words, no more hitting the fridge in the middle of the night.