A study in the current issue of Obesity Research dispels the common belief that late night eating promotes weight gain. Judy Cameron, senior scientist at Oregon Health and Science University and a psychiatry professor at the University of Pittsburgh, says the myth is based on the fact that our metabolic rate slows at night. "And, if you were to eat while your metabolic rate was slowing down," she says, "you might be more likely to store energy in the form of fat than to use it immediately."

To test that idea, Cameron and her researchers studied 16 female rhesus monkeys, who were placed on high fat diets, similar to the diet consumed by many Americans. "Some animals ate most of their food during the day at the meals they were served," she says. "Others were nibblers and nibbled a lot at night. There was a spread of eating only five percent of your calories in the evening hours and eating 65 percent of your calories in the evening hours. It turned out that the ones that ate a large percentage of their calories at night were no more likely to gain weight than the ones that ate during the day."

Cameron was surprised by the results, she says, because it was a popular notion and the recommendation of many diets to limit food intake in the evening. "It also surprised us that some animals that really increased their food intake were not gaining weight, while others that increased their food intake just a little bit gained weight," she says. "The total amount of food intake didn't correlate very well with weight gain."

Cameron says the best predictor of weight gain is activity. The monkeys in the study that gained the most weight were the ones that just sat around.