Many diets can take the weight off -- but when it comes to keeping it off, not all regimens are created equal, according to new research.
A diet consisting of high-protein foods and ones with a low glycemic index is best for maintaining weight loss, said a large European study published in the New England Journal of Medicine.
The South Beach diet is the commercial weight loss plan that most closely approximates the best diet in the study, accodring to study author Thomas Meinert Larsen from the University of Copenhagen. The Atkins diet is much higher in protein, severely limits carbs, and has a more liberal attitude towards the types of fats one may eat.
Larson cautioned that he does not endorse any particular commercial diet and believes weight loss programs should be individualized.
The study followed roughly 780 participants who had already lost weight on a calorie-restricting diet and were randomly assigned to one of five different weight management programs.
Participants who ate foods higher in protein and with a low glycemic index not only stuck to their maintenance diets better, but were also more likely to continue to lose weight over the course of the 26-week study. In contrast, those assigned to diets consisting of foods low in protein with a higher glycemic index were more likely to regain weight.
The glycemic index reflects the effects of foods on blood sugar levels. Grains that have been minimally processed, fruits, non-starchy vegetables and legumes generally have a low glycemic index, whereas processed grain foods have a high glycemic index. A raw apple, therefore, has a much lower glycemic than applesauce or apple juice.
The amount of weight regained was a little more than two pounds higher in study participants on low-protein diets compared with those on high-protein diets. Regained weight was also higher by slightly more than two pounds in participants who consumed a diet with a high glycemic index, the researchers reported.
All the diets were moderate in fat content, ranging from 25 to 30 percent of energy intake.
Unlike calorie-restricting programs such as Weight Watchers, the diet programs studied by Larson and his colleagues did not restrict caloric intake. Rather, they varied the proportion of proteins and carbohydrates. And though none of the diets were extreme, the results were still significant, according to Larson. This suggests that even small increases in protein or decreases in high glycemic index foods can make a difference in weight management.
Dr. David Ludwig, associate professor at Harvard Medical School and director of the Children's Optimal Weight for Life program said he found the results of the study particularly compelling because "rather modest changes produced significant benefits."
He added, "Increasing protein and decreasing glycemic index are separate ideas but are synergistic. That is because as you increase the protein in your diet, you are also decreasing the glycemic level."
Dr. Louis Aronne, author of the New York Times best-selling book "The Skinny" and director of the Comprehensive Weight Management Program at Weill-Cornell Medical College, said the results are consistent with clinical observations, but counter the argument made by some that a calorie is a calorie.
"I believe that a low-glycemic or high-protein approach is best and is associated with greater compliance," Aronne said.
Indeed, fewer participants in the high-protein diet groups and the low glycemic index groups dropped out of the study, the researchers found.
Some experts, however, are skeptical about the results and controversies remain about the best diet plan for overall health.
Carla Roper, a research faculty member at the New York Obesity Center, downplayed the utility of dieting in weight management.
"What we do know is that diet choice is not the definitive predictor of weight maintenance," Roper said. "Physical activity is the crucial variable in weight maintenance."
Similarly, Dr. Tim Byers, associate dean of the Colorado School of Public Health said the biggest factor in weight maintenance and overall health is physical activity, not the details of food types.
"It is not so much important what you eat after weight loss as how much you eat and how much you move," Byers said.
Although exercise is undoubtedly important for healthy living, research suggests that increasing protein and decreasing refined, processed carbohydrates will help sustain weight loss.