When it comes to long-term weight control, losing the excess flab is often easier than keeping it off. For most people, maintaining lost weight over the long-term is a far bigger challenge and yet strategies for maintaining weight loss have been the subject of far less research than how to alter dietary intake to lose the weight in the first place. So it is encouraging that a recent clinical trial looked at two different dietary manipulations to see if they might help people keep excess pounds off after losing a significant amount of weight.The study was conducted in eight European countries at several different “diet information centers”. In this study, 773 overweight and obese (initial BMI = 27 to 45) subjects who had initially lost at least 8% of their body weight (mean of 11kg) over 8 weeks on a low calorie formula diet plus vegetables (800-1000kcal) were then randomly assigned to 5 different weight maintenance diet strategies. All the experimental diets and the control group diets were lower in %fat (25-30%) than the their usual diets that averaged about 37% fat calories. In addition the various experimental diets were designed to differ in terms of their percent of calories from protein and carbohydrate and their glycemic index (GI). Subjects were randomly assigned to the 5 maintenance diet groups. Two groups were instructed to follow a lower protein diet (target of 13% calories from protein), one with a higher and one with a lower GI (targeted difference in GI = 15). The two other experimental groups were instructed to follow a high protein (target of 25% calories from protein) diet with either a high and low GI. In addition, a 5th control group was instructed to follow a maintenance diet consistent with the dietary guidelines for their various countries. All 5 groups were encouraged to consume the experimental diets ad libitum. In addition to diet instructions at two of the eight “diet centers” subjects were provided with free food to help them comply with their assigned diet. During the 6 months of follow-up 225 subjects dropped out of the study with the highest drop-out rate in the high GI, low-protein group.One problem the researchers had was compliance with the dietary instruction. As a result the targeted difference in %protein between the two low and high protein groups was not achieved (12% target but only 5.4% difference achieved). Nor was the targeted difference in GI between the two low versus high GI groups achieved as the average difference was only 4.7 GI units compared to the 15 GI units targeted. Indeed, even though the follow-up period was only 6 months urinary nitrogen measurements showed compliance was declining throughout the period. Despite these relatively modest differences in % protein and GI achieved, the researchers concluded that “....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.”1 The researchers also argued that had the subjects achieved bigger differences in GI and % protein content the differences between the groups would have been greater. However, data from all 4 experimental groups and the control group showed weight was creeping back up after the first 10 weeks. Except for the high-protein, low-GI group, all 4 other groups regained more than 1kg but less than 2Kg on average of the initial 11kg weight loss. Regression analysis showed a little less than a 1kg difference in weight regain between the high vs. low protein and high s. low GI groups. The researchers also noted that there was no differences in the subjective hunger levels between the groups. The researchers were careful about controlling % fat, fiber, and alcohol content so the modest differences between the groups were not likely related to these variables. Unfortunately, this study completely ignored the energy density (ED) of the various diets. It is certainly plausible that the ED of the higher protein and/or lower GI diets was somewhat less than the higher GI and lower protein diets, but this was not measured so we’ll never know. Indeed, the fact that all subjects were instructed consume their food ad libitum suggests there must have been something about all 5 maintenance diets that caused subjects in all groups to maintain a calorie reduction of about 500-600kcal/day over 6 month maintenance period. The most likely explanation was a combination of the moderate reduction in % fat calories, increased fiber intake, and a reduced ED of all 5 diets compared to their pre-weight loss usual diets.Bottom Line: This study suggests there may a slight advantage to instructing people interested in maintaining weight loss to bump up the % protein and reduce the intake of high-GI foods although this study provides no evidence that these variables are more important than reducing % fat and ED, which may well have been far more responsible keeping calorie intake lower and warding off increased hunger than changes differences in either % protein or GI. However, would it not be far simpler to just encourage people to lower the ED of their diet by limiting high-fat and/or dry foods, eat plenty of whole fruits and vegetables, avoid refined carbs and calorie-rich beverages? Such a strategy is far less complicated to teach people than focusing on GI and/or % protein.By James J. Kenney, PhD, RD, FACN1. N Engl J Med 2010;363:2102-13