Another study, published in the New England Journal of Medicine in 2008, assigned 322 moderately obese adults to one of three diets: calorie-restricted low-fat; calorie-restricted Mediterranean; and non-calorie-restricted low-carb. After two years, the Mediterranean group had lost an average of 9 7/10 pounds; the low-fat group, 6 4/10 pounds; and the low-carb group, 10 3/10 pounds. Although weight loss didn't differ greatly between the low-carb and Mediterranean groups, both lost appreciably more than the low-fat group did.
Unsaturated fatty acids, whether monounsaturated or polyunsaturated, can lower your levels of "bad" cholesterol (which decreases your risk of heart disease) if you eat them instead of saturated fatty acids, Hughes says. Saturated fat -- found mostly in animal products and in palm and coconut oils -- is the main dietary cause of high blood cholesterol, according to the American Heart Association.