Weight loss is a billion-dollar industry, with dieters trying everything from diet books to diet programs, and even surgery in an effort to slim down. In the quest for thinness, low-carbohydrate diets, in particular, have enjoyed a surge of popularity recently. But some experts are concerned about the safety and effectiveness of such diets, which restrict (in some cases, severely) intake of carbohydrates, such as breads, cereals, grains, fruits, and vegetables. To address that concern, researchers recently analyzed 107 previously published studies involving low-carbohydrate diets and pooled the results to see what evidence there was for the safety and efficacy of these diets. The results are published in the Journal of the American Medical Association.

Pooling previous data

Researchers from Stanford University searched medical literature databases to find articles published between January 1996 and February 2003 that involved the use of low-carbohydrate diets in the outpatient setting. They found 107 articles that encompassed 94 different dietary experiments and included a total of 3,268 subjects. They pooled the results of the studies, including effects of the diets on items such as weight, cholesterol levels, blood glucose levels, blood insulin levels, and blood pressure.

Calories are key

They found that low-carbohydrate diets were indeed effective in producing weight loss, but not necessarily because they were low in carbohydrates. It's more likely these diets worked because they restricted overall calories, say the researchers, who point out that through their review process, they uncovered high-carbohydrate diets that also restricted calories, and by this means produced weight loss.

Safety: more evidence needed

With regard to the safety of low-carbohydrate diets, the researchers found no significant "adverse effects" on items such as blood cholesterol and blood pressure, but the researchers caution that most of the published data on low-carbohydrate diets are relatively short-term (less than 90 days in many cases), making it difficult to predict their safety if they are used for longer periods of time.

Which diet will work for you?

According to this review, the diets that yielded the most weight loss were those that restricted calorie intake, were longer in duration (four and half months or more), and involved subjects who were significantly overweight at the outset. The researchers suggest that these three factors "may be more important predictors of weight loss than carbohydrate content."

The authors go on to say that, according to this review, "there is insufficient evidence to make recommendations for or against the use of low-carbohydrate diets." But they and the author of an accompanying editorial¹ make it clear that, because of the popularity of such diets and because of the rising obesity problem in America, further studies of these diets are urgently needed.

In the meantime, see your doctor before beginning any weight-loss regimen, and remember that the only diet that will help you keep weight off for life is a diet that you can follow for life.