At any given time, at least a third of American adults are trying to lose weight. Most established health guidelines suggest a calorie-reduced, low-fat, high-carbohydrate eating plan for weight loss. However, low-carbohydrate, high-fat, and high-protein diets - like the Atkins diet - are increasingly popular, even though there is little scientific evidence supporting either their effectiveness or their safety. Two new studies, published in the New England Journal of Medicine, compared an Atkins-style diet with a conventional, low-fat, low-calorie, high-carbohydrate diet.

Low-carb vs. low-fat

In one study researchers from several Philadelphia universities randomly assigned 132 very overweight adults to either a conventional, calorie-restricted, low-fat diet (based on the National Heart, Lung, and Blood Institute guidelines) or a low-carbohydrate diet (30 grams, or less, a day), for 6 months. The volunteers attended weekly 2-hour classes to learn about their eating plan for 4 weeks, and then monthly 1-hour sessions thereafter. They received handouts that explained their assigned diets, how to read nutrition labels and count carbohydrates and calories, and sample menus and recipes.

In a second study that took place at several universities throughout the United States, investigators made a similar comparison. They assigned 33 overweight adults to a low-carbohydrate, Atkins-style diet and another 30 volunteers to a conventional, low-fat diet. The volunteers received written materials on their prospective diets and briefly met with a registered dietitian for instruction and review four times throughout the one-year study. By minimizing contact with a nutrition professional, the researchers hoped to mimic how the majority of people typically approach weight loss.

In both studies, the volunteers on the low carbohydrate diet lost a little more weight after 6 months than those on the conventional diet. However, after a year - only the second study went beyond 6 months - there was no significant difference in the amount of weight lost. The volunteers following the low-carb diet showed improved triglyceride levels, but other health markers - insulin sensitivity, cholesterol levels, and blood pressure - were not consistently different between the two groups.

Doubts remain

The authors of both studies conclude that health care providers should not recommend low-carbohydrate diets without further investigation. After one year, the low-carbohydrate dieters regained more of their lost weight than the low-fat dieters, which may indicate that the diet is more difficult to stick with than a low-fat diet. Also, the high dropout rate and the relatively small amount of weight lost underscores how difficult it is to actually achieve substantial and sustained weight loss.

Eating advice for everyone

Overweight people should not be discouraged, but rather, they should recognize that it is challenging to alter diet and exercise habits. With this in mind, dieters should aim to make small changes that they can maintain over time. Despite the popularity of the low-carb craze, most health professionals recommend the same diet for weight loss and healthful eating. That is a diet based on whole grains, fruits, vegetables, and limited amounts of saturated fat.