This past March, Stanford University researchers published the results of one of the longest and most persuasive comparisons of weight-loss programs ever conducted. Three of the four diets in the study are heavily promoted regimens that have made their originators famous: the Atkins diet and the Zone diet, which both emphasize high-protein foods, and the Ornish diet, a plan that prohibits most fatty foods. The fourth was the no-frills, low-fat diet that most nutrition experts recommend.

The results, published in the Journal of the American Medical Association, were a surprise because they seemed to overturn the conventional wisdom. The experts’ low-fat diet was beaten by Atkins’s steak dinners and bacon-and-egg breakfasts. A year after starting their diets, people on the Atkins plan—which unapologetically endorses high-fat protein such as meats and dairy products to keep dieters sated—had dropped an average of 10 pounds. Subjects on the other diets had lost between three and six pounds. And members of the Atkins test group showed no jump in blood cholesterol levels, despite the high levels of cholesterol in their diet. Reporters jumped on the obvious headlines: “Atkins Fares Best ...” stated the Washington Post. “Atkins Beats Zone, Ornish and U.S. Diet Advice,” the Associated Press declared. It was the same everywhere else: Atkins had bested the competition.

The newspaper accounts were not wrong. But the lead author of the Stanford study suggests a different interpretation of the findings. “What happened in our study was very modest weight loss in all four groups,” says Christopher D. Gardner, a nutrition scientist at the Stanford Prevention Research Center. All groups also showed improvement in individuals’ levels of cholesterol, blood pressure and insulin, even though none of them followed their diet plans exactly. And far from overturning established ideas about low-fat diets, the Stanford investigation provided resounding confirmation of another generally held belief: most people who try to lose weight, on any kind of diet, will succeed, even if many of them regain the weight later.

Contrast those conclusions with the results of another study published in the April issue of American Psychologist by researchers at the University of California, Los Angeles. They analyzed 31 long-term diet studies and found, as Gardner said, that most participants did see results—losing about 5 to 10 percent of their total body mass. And they did it while on all kinds of diets. But most also regained all that weight over the longer term, and some put on even more than they had lost. Only a small minority of subjects in the 31 studies kept the extra pounds off. The researchers’ conclusion?

Eat in moderation and exercise regularly. (This statement parallels similar advice nutritionist Marion Nestle presents in the accompanying article.) Gardner thinks the traditional exhortation to cut dietary fat has turned out to be a bad message. The public health experts got it wrong, he says: “It totally backfired on us.” People who consumed less fat often turned to soda and similar corn-syrup-sweetened products, along with other refined, low-fiber, carbohydrate- rich foods. As a result, “the obesity epidemic has continued to grow. Calories have continued to creep up, and it’s been predominantly in the refined carbohydrates.”

The Atkins plan, which advises dieters to be less concerned about fat, steers people toward vegetables and protein and away from sugars and refined carbohydrates. “Maybe low carb is a better simple message to the public than low fat,” Gardner says. “We tell them low carb, and they get it. They cut out a couple of sodas or a couple of cookies, and that adds up.”

James Hill, a psychologist and authority on weight loss, agrees that the Atkins approach has virtues. “The Atkins diet is a great way to lose weight,” he says. But it “is not a way to keep weight off,” he asserts. “There’s no way you can do it forever.”

Hill is not terribly interested in comparing diets or devising new ones. “I think the weight-loss part is something we do pretty well,” he says. One of his areas of research concerns individuals who have reduced their weight and sustained it. Hill and Rena Wing of Brown University have established what they call the National Weight Control Registry to collect data on people who have cut at least 30 pounds and kept them off for a year. Many have lost much more—the average is a 70-pound weight loss maintained for six years. “If you look at how they lost weight, there’s no commonality at all,” Hill says. But “if you look at how they kept it off, there’s a lot of commonality.”

The key, he continues, is exercise. “Activity becomes the driver; food restriction doesn’t do it. The idea that for the rest of your life you’re going to be hungry all the time—that’s just silly.” People in the registry get an average of an hour of physical activity every day, with some exercising for as much as 90 minutes a day. They also keep the fat in their diet relatively low, at about 25 percent of their calorie intake. Nearly all of them eat breakfast every day, and they weigh themselves regularly. “They tell us two things,” Hill says. “The quality of life is higher—life is better than it was before.” And “they get to the point with physical activity where they don’t say they love it, but they say ‘it’s part of my life.’”

Hill admits that fitting an hour or more of exercise into the day is difficult, which is why he also focuses on prevention. Many of these people might never have become obese initially if they had exercised a mere 15 to 20 minutes a day. “I think you pay a price for having been obese,” he states, “and you have to do a lot of activity to make up for that.”