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Comparing Diets: What the Research Shows

by Berkeley Wellness

At any given time, hundreds of weight-loss diets are vying for eyeballs online or shelf space in bookstores—not counting the multitude of get-thin-quick schemes, from fat-melting creams and supplements to detox purging and fasting. Few diets have been tested in studies; most are rehashes of previous diets with a few new twists or gimmicks. New diet “breakthroughs” get lots of attention because most people fail with the existing programs and thus keep hunting for one that will finally work. And the publicity machines behind this multi-billion-dollar industry encourage dieters in their wishful thinking.

During the last decade, a few dozen good independent clinical trials have compared leading diets or general types of diets (such as low-carb or low-fat). Most have found very modest differences in weight loss after several months to a year—and no consistent winner. Keep in mind, however, that nearly all diet studies report average results, which disguise the fact that some people lose a lot of weight, some a small amount, and others stay the same or even gain weight. One consistent finding is that adherence to the regimens is a far stronger predictor of weight loss than are the specifics of the diets. Even when people do stay on diets, they usually stray from the rules, and this worsens over time, though professional support and guidance help.

Studies and reviews of popular diets

  • Low-carb vs. low-fat. The latest in a string of such head-to-head studies appeared in the Annals of Internal Medicine in September 2014. For a year middle-aged obese people followed either a moderately low-carb diet (similar to the maintenance phase of the Atkins diet) or a modestly low-fat diet (similar to American Heart Association guidelines). Participants received intensive counseling, but no specific calorie goals; they did not change their exercise habits. After a year, average weight loss was small—about 12 pounds for the low-carb group and 4 pounds for the low-fat group. This specific low-carb diet led to bigger dietary changes and greater calorie reduction, so it resulted in greater weight loss. It’s not known if participants would have done as well if they had not been given fairly intensive counseling.

  • The bigger picture. Also in September 2014, an analysis of 48 studies of popular diets (including Atkins, Zone, Weight Watchers, Jenny Craig, Ornish, and South Beach) was published in the Journal of the American Medical Association. It found that all diets—low-fat, low-carb, or somewhere in between—were modestly effective after a year (9 to 16 pounds lost), with little difference in weight loss from one plan to another. Behavioral support and exercise enhanced weight loss.
  • The bigger picture II. Similarly, a Canadian review in Circulation: Cardiovascular Quality and Outcomes in November 2014 looked at 12 clinical trials involving Atkins, South Beach, Weight Watchers, and Zone. It found that all resulted in “modest and similar weight loss” (ranging from 4 to 12 pounds) after a year—but so did control groups who got “usual care” (such as self-help materials or nutritional counseling). Weight loss was front-loaded—that is, greatest during the first six months—and after that, weight gradually crept back. The few studies lasting two years found increasing weight regain.
  • Structured programs may do best. In a review in the Annals of Internal Medicine in April 2015, Johns Hopkins researchers looked at 39 clinical trials involving 11 weight-loss programs. It concluded that only Jenny Craig and Weight Watchers had evidence to support claims that they promote long-term weight loss (for at least one year). But even they resulted in only 3 to 5 percent greater weight loss than seen in control groups who relied on printed health information or other forms of counseling. For the other programs studied, results were even more modest or there were no long-term data.

Maintaining Weight Loss: The Hard Part

The strategies needed to lose weight may be different from those you need to maintain your new, lower weight.

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