Despite the plethora of diet books available today, there is a scarcity of scientific research on the health effects of popular eating plans. Researchers decided to compare diets to see how well they reduced weight and decreased cardiac risk factors. The diet comparison included the Atkins diet, which involves carbohydrate restriction; the Zone diet, which balances macronutrients; Weight Watchers, which restricts calories; and the Ornish diet, which restricts fat intake.

To compare diet plans, a total of 160 overweight subjects were randomly assigned to one of these diets during an 18-month study at an academic medical center in Boston. At the end of the study period, the researchers reported that each diet “modestly” reduced body weight and several cardiac risk factors. Each diet also significantly reduced HDL-to-LDL blood cholesterol ratios and positively affected blood pressure and glucose levels. Unfortunately, overall dietary adherence rates were low for all four food plans, despite the fact that increased adherence was associated with greater weight loss and cardiac risk factor reductions in each diet group.

Reporting in the January 5 issue of The Journal of the American Medical Association (JAMA), the researchers concluded that “adherence level rather than diet type was the key determinant of clinical benefits.” They also recommended future research to “identify practical techniques to increase dietary adherence, including techniques to match individuals with the diets best suited to their food preferences, lifestyle and medical conditions.”