On Nutrition: Need To Lose Weight? Try Fasting

It's been dissed as a fad, but skipping meals might actually be smart.

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Staff writer Katherine Hobson

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If your pants mysteriously shrink during the holiday season, you may want to consider a weight-loss method with a bad reputation: skipping meals. Though conventional wisdom has held that if you fast or omit meals you will only make up for it by eating more later on, some experts advocate just those methods—not only to control your weight, but also to gain other health benefits.

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First, let's look at the weight factor. The data have been consistent, says David Levitsky, a professor of nutrition and psychology at Cornell University. If you skip a meal or downsize it, you do feel hungrier at the next one—but you don't make up for all of the calories you avoided, he says. In one unpublished study, his research team gave one group of people a commercially available small lunch (yogurt, soup, or some other small snack) adding up to about 200 calories, while a second group had regular buffet lunches of about 600 calories. Both groups were told to eat as they wished during 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. "You don't compensate precisely for skipping a meal or reducing it," says Levitsky.

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Heresy of heresies: He contends that this even extends to skipping—or skimping on—breakfast. (Since some studies have shown that most people get a lot of fiber at breakfast, however, you might want to consider eating a fiber-rich meal, like a bowl of cereal, at lunch if you don't earlier.)

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A variation that also may lead to weight loss is restricting calories on alternate days. In a small study published in March, researchers followed a group of 10 people with a body mass index above 30 who were fed just 20 percent of their normal calorie intake on alternate days. On the other days they could eat what they wanted. After eight weeks, they'd lost an average of 8 percent of their body weight. These people were also asthma patients, and their symptoms also improved significantly after two weeks on the regimen, says study author James Johnson, a clinical instructor in the department of surgery at Louisiana State University School of Medicine.

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What about plain old fasting? A study presented at an American Heart Association conference earlier this month suggested that skipping meals on a regular basis might protect against heart disease. Researchers in Utah looked at the rates of heart disease among Mormons, who are supposed to fast on the first Sunday of every month (they're also instructed to avoid caffeine and alcohol). It also looked at the habits and disease rates among a smaller number of non-Mormons. Among health or lifestyle behaviors that made a difference in the risk of heart disease, only fasting was found to be significant: It didn't matter if you were Mormon or not; if you fasted, you had a smaller chance of having heart disease.

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"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 the University of Utah and Intermountain Medical Center in Salt Lake City. That's only a theory based on what researchers have noted in animals, says Horne, who says most studies on the mechanisms and effects of fasting and calorie restriction have been done in rodents, roundworms, and slugs.

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Still, there's plenty of evidence from those animal studies to suggest that restricting calories—either by a consistently reduced food intake, skipping meals, or fasting—might be good for humans, too, says Mark Mattson, a neuroscientist at the National Institute on Aging who was also an author of the asthma study. He says there are at least two possible mechanisms. Eating less cuts down on the production of free radicals, which damage cells and can lead to disease. He also says that 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," says Levitsky. "We don't know about living a longer life, but all the markers are in a favorable direction."