Raise Protein, Cut Glycemic Index to Maintain Weight Loss

A modest increase in protein content and a modest decrease in glycemic index values allowed study subjects to maintain a 10-kg weight loss better than did other dietary manipulations, according to a randomized trial reported in the Nov. 25 issue of the New England Journal of Medicine.

More subjects also were able to continue losing weight while consuming this combination of high-protein, low-glycemic-index foods, said Thomas Meinert Larsen, Ph.D., of the University of Copenhagen and his associates in the Diet, Obesity, and Genes (Diogenes) study.

The Diogenes study was designed to assess the efficacy of five different maintenance diets in preventing weight regain after obese subjects lost at least 8% of their body weight during an 8-week low-calorie diet. The maintenance diets all contained moderate amounts of fats (25%-30% of total energy consumed), all allowed unrestricted caloric intake, and all attempted to keep alcohol and fiber contents comparable, varying only in their protein content and glycemic indexes.

The study was conducted at research centers throughout Europe. A total of 773 subjects who achieved their target weight loss during the low-calorie-diet period were randomly assigned to continue a 26-week maintenance phase following a diet low in protein (13% of total energy consumed) with a low glycemic index; a diet low in protein with a high glycemic index; a diet high in protein (25% of total energy consumed) with a low glycemic index; a high-protein, high-glycemic index diet; or a control diet with moderate protein content and no guidelines regarding glycemic index (N. Engl. J. Med. 2010;363:2102-13).

The study subjects received dietary counseling every other week for 6 weeks, and then monthly thereafter. They were given recipes, cooking instructions, behavioral advice, and a teaching system to help them achieve the targeted composition of macronutrients. Periodically, they weighed their food and completed food diaries for 3 consecutive days to facilitate monitoring of adherence. Adherence declined in all groups toward the end of the study.

A total of 29% of the subjects dropped out of the study during this 6-month maintenance phase, a rate nearly 10% higher than expected. Nevertheless, the Diogenes participants "were probably a more adherent group than participants in other studies, since they had adhered sufficiently to the low-calorie diet for 8 weeks to lose at least 8% of their body weight," Dr. Larsen and his colleagues said.

"Despite issues of adherence, we believe that our results are generalizable to obese people, particularly if diets are facilitated by easy access to low-glycemic-index foods and a culture that supports these dietary changes," they added.

Weight regain was significantly higher in the low-protein groups and the high-glycemic-index groups. In contrast, both the high-protein and low-glycemic-index groups were more likely to maintain their weight loss and to lose an additional 5% of their body weight.

Only subjects assigned to the group with low-protein content and high glycemic index showed significant weight regain – a mean of almost 2 kg.

The study subjects reported no between-group differences in feelings of satiety, "though we suspect that the effects were too subtle to be subjectively perceived or measured with the use of visual analog scales," Dr. Larsen and his associates said.

These findings show that "even a modest increase in dietary protein or a modest reduction in glycemic-index values was sufficient to minimize weight regain and promote further weight loss in obese patients after a successful weight-loss diet," Dr. Larsen and his associates concluded.

This study was funded by the European Commission. Dr. Larsen and his colleagues reported ties to more than 100 food companies and numerous drug companies.