Constant controversy swirls about which kind of weight-loss diet works best, but there is precious little scientific evidence comparing one diet to another. To provide some real diet data, a recent Journal of the American Medical Association (JAMA) study pitted the Atkins, Zone, LEARN, and Ornish diets against each other in a year-long head-to-head study.

In these four diets, the amounts of allowed protein, fat, and saturated fat are inversely proportional to the amount of each diets carbohydrate content. Atkins is a very low carb diet, high in protein and fat. The Zone is relatively low carb. The LEARN (Lifestyle, Exercise, Attitudes, Relationships, and Nutrition) diet follows national dietary guidelines and is low in fat and high in carbs. Ornish is the highest carb diet.

The study followed 311 non-diabetic overweight or obese pre-menopausal women for one year, after randomly assigning them to one of the four diet plans. They received weekly instruction for eight weeks and then an additional ten-month follow-up. It was the longest and largest study to compare Atkins to other diets.

Those assigned to the Atkins plan, which allows an abundance of meat, fats, and some vegetables but severely limits carbohydrates, had more weight loss and more favorable outcomes for metabolic effects than women on the other three diets. The amount of weight loss at twelve months relative to baseline was 2% to 5%. Average weight loss was 10.4 pounds for Atkins; 3.5 pounds for the Zone; 5.7 pounds for LEARN; and 4.8 pounds for Ornish.

Lipid levels and blood pressures for the Atkins group were comparable or even better than for the other three groups. Fasting glucose concentrations and fasting insulin were not statistically different among the groups. Concerns about possible bad metabolic effects of the Atkins diet were not substantiated during the year. It was not known whether the benefits shown by the Atkins diet were due to the low carb intake or to the high protein intake.

Of course, if youre thinking of changing your diet, a consultation with your healthcare team is advised. However, the researchers did note that their findings should ease the concerns of doctors whose patients want to lose weight by following a low carb, high protein, high fat diet.

Sources: JAMA, March 2007
Atlanta Journal-Constitution