Which Weight Loss Diet Works Best? A New Study Ranks the Evidence

by Alice Park
from Time.com

With the American Medical Association now urging doctors to treat obesity as a medical condition, physicians should be screening and treating overweight and obesity just as they would any other chronic disorder. But when it comes to figuring out which methods are proven to work best, physicians may find themselves at a loss. Some studies have found that commercial weight-loss programs work about the same when it comes to the amount of weight they can help consumers lose, while others found that low-carb diets beat out low-fat plans.

To make sense of the noise, Kimberly Gudzune, an assistant professor of medicine at Johns Hopkins University, and her colleagues searched the scientific literature for studies on 11 commercial weight-loss programs. In their results, publishedMonday in the Annals of Internal Medicine, they assessed which ones have the best data to support them. But they also found there weren’t that many studies actually tracking how much weight people on the programs lose.

Gudzune decided to focus on commercial programs like Weight Watchers and NutriSystem, among others. And of 4,212 studies that involved these diets, only 45 were done under the gold scientific standard of randomly assigning people to a weight-loss program or not, and then tracking their weight changes over time. “The majority [of programs] still have no rigorous trials done,” says Gudzune.

According to her analysis, only two programs, Weight Watchers and Jenny Craig, helped dieters to lose weight and keep it off for at least a year. Those on Weight Watchers shed nearly 3% more of their starting weight after 12 months than those not dieting, and Jenny Craig users lost nearly 5%. Other programs, including Atkins, the Biggest Loser Club and eDiets, also helped people drop pounds, but since the studies only lasted three to six months, it’s impossible to know if that weight loss lasted.

The modest weight loss “may be disappointing to many consumers,” says Gudzune, but she notes that weight-management guidelines suggest that a 3% to 5% sustained weight loss is an important first step toward a healthy weight. “Even that small amount of weight loss can help to lower blood sugar, improve cholesterol profiles, help to lower blood pressure and ultimately prevent things like diabetes,” she says.

“Would 6% or 8% or 10% of body weight lost be better? Yes, but it’s not like the interaction is totally linear,” says Gary Foster, chief scientific officer of Weight Watchers International. Over time, weight-loss rates may change, and other studies show they typically slow after the initial blush of success.

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