You've heard the reason not to: You'll only eat more later on. But people don't automatically replace all the missed calories at their next meal, says David Levitsky, a professor of nutrition and psychology at Cornell University. His research team assigned one group of people small lunches of about 200 calories, while a second group dined on about 600 calories. Both ate as they wished the rest of the day. After two weeks, the small-lunch bunch lost weight; they were eating about 400 calories fewer than the all-you-can-eaters.
A variation that might not even feel like self-denial is to restrict calories every other day. In a small study published in March, researchers followed a group of 10 overweight people who were fed just 20 percent of their normal calorie intake on alternate days. The other days, they could eat what they wanted. After eight weeks, they'd lost an average of 8 percent of their body weight, says study co-author James Johnson, a clinical instructor in the department of surgery at Louisiana State University School of Medicine and author of a forthcoming book on alternate-day calorie restriction.
"I like the psychology of it," says Kenneth Webb, 37, a hedge fund trader from Walnut Creek, Calif., who's followed Johnson's program. "On the down days, you've got hope for tomorrow — who can't diet for one day? And on an up day, you've got no guilt about it."
Webb calculated his calorie needs based on his level of activity and eats just 30 percent of that one day; the next, he eats 130 percent. He's lost 30 pounds since July.
Besides shrinking the waistline, skipping meals regularly might protect against disease. A study presented in November at an American Heart Association conference compared the rates of heart disease among Mormons, who are supposed to fast on the first Sunday of every month, with the habits and disease rates among a smaller number of non-Mormons.
Controlling for other behaviors that make a difference in the risk of heart disease, the researchers found that fasting seemed to be significant: If you fasted, you had a smaller chance of having heart disease.
"The thought from a biological perspective is that fasting rests the metabolism for a day and resensitizes the body's cells to glucose and insulin," says study author Benjamin Horne, who researches heart disease at Intermountain Medical Center and the University of Utah in Salt Lake City. That's only a theory, he notes, since most studies on calorie restriction have been done in rodents, roundworms and slugs.
Less is more
Still, there's plenty of evidence from the animal studies to suggest that some sort of calorie-restricted eating plan might be good for humans, too, says Mark Mattson, a neuroscientist at the National Institute on Aging who was also an author of the alternate-day study. (That study focused on asthma sufferers, whose symptoms improved more when they reduced their intake than seemed attributable to just losing weight.)
Eating less cuts down on the production of free radicals, which damage cells and can lead to disease, Mattson says. And there's a cellular response similar to what happens when we exercise. Like working out, going without calories is mildly stressful to the cells at the time but beneficial over the long run.
"Dietary restriction is about the best dietary advice I can give you," Levitsky says. "We don't know about living a longer life, but all the markers are in a favorable direction."
You may have noticed, though, that the bottom line of any of these techniques is cutting the overall number of calories you eat. Webb, for example, has effectively reduced his average daily caloric intake to 80 percent of what it used to be. Like Webb, many people may find that skipping a meal or two a week, or taking a day every month entirely away from food or eating a lot less during a given meal or every other day, is far more appealing than making the sacrifice all the time.