Comparison of Weight-Loss Diets With Different Compositions of Fat, Protein, and Carbohydrates

Types of diet used for treating overweight people include those that emphasize protein, those that emphasize carbohydrates, or those that emphasize fat. There is considerable controversy about which is most effective. This randomized clinical trial compared the effects on the body weight of overweight individuals of 4 energy-reduced diets that differed in their targeted percentage of macronutrients. A total of 811 overweight adults aged 50 to 52 years were randomized to receive to 1 of 4 diets containing fat, protein, and carbohydrates in the following proportions: 20%, 15%, and 65% (group 1, n = 204); 20%, 25%, and 55% (group 2, n = 202); 40%, 15%, and 45% (group 3, n = 204); and 40%, 25%, and 35% (group 4, n = 201). Each diet contained similar foods. Individual and group instructional sessions were offered to the participants. At 6 months, participants in each group had a mean weight loss of 6 kg (7%) of their initial weight. After 12 months, all groups slowly regained body weight. The amount of weight loss was similar after 2 years among participants assigned to a diet containing 15% or 25% protein (3.0 and 3.6 kg, respectively; among those assigned a diet of 40% or 20% fat (3.3 kg for each); and in those assigned to a diet with 65% or 35% carbohydrates (2.9 and 3.4 kg, respectively) (P > 0.20 for all comparisons). The average weight loss among the 80% of participants who completed the trial was 4 kg and at least 10% of initial body weight was lost in 14% to 15% of the participants. At 2 years, there were no differences among the diets in satiety, hunger, diet satisfaction, and attendance at group sessions. A strong association was found between attendance and weight loss. Risk factors for cardiovascular disease and diabetes were reduced by all the diets. These findings show that reduced-calorie diets that emphasize a range of fat, protein, and carbohydrate compositions are equally beneficial in producing clinically meaningful weight loss and the maintenance of weight loss over 2 years.