Diets with high or low protein content and glycemic index for weight-loss maintenance

Abstract

Background: Studies of weight-control diets that are high in protein or low in glycemic index have reached varied conclusions, probably owing to the fact that the studies had insufficient power.

Methods: We enrolled overweight adults from eight European countries who had lost at least 8% of their initial body weight with a 3.3-MJ (800-kcal) low-calorie diet. Participants were randomly assigned, in a two-by-two factorial design, to one of five ad libitum diets to prevent weight regain over a 26-week period: a low-protein and low-glycemic-index diet, a low-protein and high-glycemic-index diet, a high-protein and low-glycemic-index diet, a high-protein and high-glycemic-index diet, or a control diet.

Results: A total of 1209 adults were screened (mean age, 41 years; body-mass index [the weight in kilograms divided by the square of the height in meters], 34), of whom 938 entered the low-calorie-diet phase of the study. A total of 773 participants who completed that phase were randomly assigned to one of the five maintenance diets; 548 completed the intervention (71%). Fewer participants in the high-protein and the low-glycemic-index groups than in the low-protein-high-glycemic-index group dropped out of the study (26.4% and 25.6%, respectively, vs. 37.4%; P=0.02 and P=0.01 for the respective comparisons). The mean initial weight loss with the low-calorie diet was 11.0 kg. In the analysis of participants who completed the study, only the low-protein-high-glycemic-index diet was associated with subsequent significant weight regain (1.67 kg; 95% confidence interval [CI], 0.48 to 2.87). In an intention-to-treat analysis, the weight regain was 0.93 kg less (95% CI, 0.31 to 1.55) in the groups assigned to a high-protein diet than in those assigned to a low-protein diet (P=0.003) and 0.95 kg less (95% CI, 0.33 to 1.57) in the groups assigned to a low-glycemic-index diet than in those assigned to a high-glycemic-index diet (P=0.003). The analysis involving participants who completed the intervention produced similar results. The groups did not differ significantly with respect to diet-related adverse events.

Conclusions: In this large European study, a modest increase in protein content and a modest reduction in the glycemic index led to an improvement in study completion and maintenance of weight loss. (Funded by the European Commission; ClinicalTrials.gov number, NCT00390637.).

Figure 1. Screening, Randomization, and Follow-up of Study Participants

HGI denotes high glycemic index, HP high protein, LCD low-calorie diet, LGI low glycemic index, and LP low protein.

Figure 2. Total 24-Hour Urinary Nitrogen Excretion and Changes in Body Weight

Panel A shows 24-hour urinary nitrogen excretion, as a marker of dietary protein intake, from the time before the low-calorie diet (LCD) was initiated through the end of the weight-maintenance intervention. Panel B shows the change in weight for each of the dietary groups during the weight-maintenance intervention, adjusted for body-mass index at randomization, weight loss during the low-calorie-diet phase, sex, family type (single-parent family, two-parent family with one parent as participant, or two-parent family with both parents as participants), center, and age at screening, on the basis of an intention-to-treat mixed-model analysis. The changes in body weight from randomization to week 26 among participants who completed the intervention are also shown (boxes). All participants who underwent randomization and for whom data on weight at the time of randomization were available were included. HGI denotes high glycemic index, HP high protein, LGI low glycemic index, and LP low protein.