Saturday, July 14, 2012

Does late-night eating make you fat? By Jerry Brainum

   One of the axioms in dieting is that you should never eat food past a certain time of day. For some, that means not eating anything past dinnertime, or about 6 p.m., although the time varies with individuals. The basic rule, however, is that you should eat the majority of your calories while you’re most active—for most people during the day. That way you’re more likely to burn off excess calories.
     Various popular diets continue to promulgate this dictum, including the Atkins and South Beach diets. Many bodybuilders adhere to the no-late-night-eating rule, mainly because metabolism drops during sleep, making it easier to retain calories and either stay or get fat.
   On the surface the advice makes sense. After all, when you’re inactive, where do the calories go? Research confirms that the metabolic rate drops during sleep in both humans and various animal species, but studies examining the effects of late-night or evening eating provide conflicting results. One study of women, for example, showed that those who ate at night gained weight over two weeks.
People who work the night shift are often heavier and gain more weight than their daytime peers. That’s curious since the night shift workers are ostensibly awake and active. Those who get more than half their total calorie intake at night gain weight faster than those who eat mostly during the day.
     Other research, however, shows little or no effect of night eating. A 10-year study of more than 7,000 people showed no connection between night eating and weight gain. Some studies do show that those who are obese tend to eat more at night than slimmer types, while another study found that those who tended to eat late were slimmer than usual. Confusion abounds.
     The most recent study to examine the late-night-eating controversy featured rhesus monkeys as subjects.1 They could be closely monitored, with every morsel of food and activity accounted for. All of the monkeys were female, and their ovaries were removed—a known cause of weight gain. The monkeys were also put on high-fat diets, another established mechanism of weight gain. No monkeying around in this study.
The number of calories the monkeys consumed at night made little or no difference in their tendency to gain weight. Despite a diet that contained 368 percent more calories than their usual intake, most of the monkeys didn’t gain much. The authors suggest that the monkeys’ bodies successfully disposed of the excess calories through a thermogenic mechanism; that is, the excess calories were converted into heat, not stored.
When you overeat, your metabolism temporarily increases as a way of compensating for the extra calories. In addition, increasing fat stores aren’t related to a particular eating time but to a continued surfeit of calories over the course of several days. In short, people get fat because they overeat in relation to their physical activity level day after day. Contrary to popular belief, although your metabolism does drop when you sleep, that doesn’t automatically translate into weight gain.
    In fact, one eating plan frequently discussed in IRON MAN, the Warrior Diet espoused by Ori Hofmekler, suggests that you should get a large percentage of your calories at night. Hofmekler claims that such eating promotes a more efficient use of nutrients. One thing is certain, however: If you want to eat at night, go ahead. What’s important is not when you eat, but how much.        
1 Sullivan, E.L., et al. (2005). Evidence in female rhesus monkeys that nighttime caloric intake is not associated with weight gain. Obesity Res. 13:2072-2080.

©,2012, Jerry Brainum.Any reprinting in any type of media, including electronic and foreign is expressly prohibited.