Many popular diets emphasize either carbohydrate, protein or fat as the best way to lose weight.
However, there have been few studies lasting more than a year that evaluate the effect on weight loss of diets with different compositions of those nutrients. In a randomized clinical trial led by researchers at the Harvard School of Public Health (HSPH) and Pennington Biomedical Research Center of the Louisiana State University System, a comparison of overweight participants assigned to four different diets over a two-year period showed that reducing calories achieved weight loss regardless of which of the three nutrients was emphasized. The study, which was funded by the National Heart, Lung, and Blood Institute (NHLBI) of the National Institutes of Health, appears in the February 26, 2009 issue of The New England Journal of Medicine.
"This is important information for physicians, dieticians and adults, who should focus weight loss approaches on reducing calorie intake," said Frank Sacks, professor of cardiovascular disease prevention at HSPH and lead author of the study.
The NEJM issue includes an accompanying editorial on the study's findings.
The trial included 811 men and women who were randomly divided into four diet groups with different target nutrient compositions:
- Low-fat, average protein: 20% of calories from fat, 15% of calories from protein, 65% of calories from carbohydrate
- Low-fat, high-protein: 20% fat, 25% protein, 55% carbohydrate
- High-fat, average protein: 40% fat, 15% protein, 45% carbohydrate
- High-fat, high-protein: 40% fat, 25% protein, 35% carbohydrate
The participants were diverse in age, sex (62% women, 38% men), geography and income. The diets followed heart-healthy principles, replacing saturated with unsaturated fat and were high in whole cereal grains, fruits and vegetables. Each participant received a diet prescription that encouraged a 750-calorie reduction per day, however none were less than 1,200 total calories per day. Participants were asked to do 90 minutes of moderate exercise each week. They recorded their daily food and drink intake in a food diary and in a web-based program that provided information on how closely they were meeting their dieting goals. Individual counseling was provided every eight weeks over two years and group sessions were held three out of four weeks during the first six months and two out of four weeks from six months to two years.