The longest (2 years) and largest (~800 people) randomized control trial (the gold standard of studies) reported in the New England Journal of Medicine (2/27/09) was designed to answer the seemingly age-old question What’s the Best Diet for Weight Loss? The study was funded by National Institutes of Health and conducted by leading obesity researchers from Harvard School of Public Health and Pennington Research Center in Louisiana.
People were randomly assigned to one of four diets made up of varying percentages of calories from carbohydrate (low of 35% to high of 65%), protein (low of 15% to high of 25%) and fat (low of 20% to high of 40%). (For frame of reference: Americans eat about 45-50 % of calories as carbohydrate, 30-35% as fat and 15-20 % as protein.) People were provided with group and individual counseling throughout the study (with more support early in the study) including support for behavioral change. Eighty percent of people completed the study.
And the drum roll, please…No one diet faired better than another! People lost a similar amount of weight 7% (6 kg/13 lbs) from their initial weight by 6 months. After 12 months people regained similar amounts of weight and at 2 years weight loss remained similar at 4 kg/9 lbs. The satiety, hunger and satisfaction ratings were similar across all diets.
Though the weight lose appears minimal, at least by Biggest Loser standards, this amount of weight loss (all diets) reduced cardiovascular disease and type 2 diabetes risk factors including improved LDL-cholesterol, lower blood glucose, lower serum insulin levels and lower blood pressure. Interestingly, but again not surprising, the people who attended more counseling sessions had greater weight loss—people who attended 2/3rd of sessions lost about 9 kg/20 lbs.
People modified the nutrient composition of their diets in the direction of the goals of the diets they were assigned to but they didn’t reach the diet’s goals. This finding underscores the point that people gravitate to dividing their calories into carbohydrate, protein and fat based on their personal and cultural food preferences.
Bottomlines: This study shows that a variety of healthy eating plans can be effective for weight loss. People should be encouraged to use a healthy eating plan that fits their eating style and preferences for today, tomorrow and years to come. Check out my book Diabetes Meal Planning Made Easy for just this type of guidance whether you have diabetes or just want to eat healthier. This study also reinforces a point commonly made in long term weight control studies: people need continual and continued support to achieve and maintain weight loss.