High-protein and low-glycemic diets (reducing carbohydrates) improve dietary compliance and maintenance of weight loss in overweight adults who have lost weight on a low-calorie diet.…
Long-term weight maintenance is difficult, and there is very limited and variable evidence about the value of altering macronutrient composition in order to improve weight maintenance for periods of 6 months or longer. A higher protein diet has been shown to be useful in some longer studies, but there are no data to support a low-glycemic index (GI) diet.
A total of 1209 overweight and obese adults (body mass index between 27 and 45) were recruited from eight European countries. Eligible participants were aged between 18 and 65 and had at least one healthy child. They were invited to take part in an 8-week low-calorie diet (3.3-4.2 MJ), and those who achieved at least an 8% weight loss were eligible to participate in a 6-month weight-loss maintenance trial. Of the 938 who took part in the diet, 773 were then randomized to one of four dietary maintenance interventions: a high protein (25% of energy) or a low protein (13% of energy), with either a high-GI diet or low-GI diet (15 GI units lower than high GI); alternatively, they were randomized to a control diet with an average protein level. Fat content was 25-30% of energy and the diets were ad libitum. Two centers provided study food to the volunteers from a shop, whereas six centers provided instruction only. The five groups did not differ in age, weight or weight loss during the low-calorie diet, but blinding is not mentioned in the article. The outcomes reported in this article were weight, fat and lean mass, waist and hip circumference and 24 h urinary urea and plasma urea.
A total of 548 participants completed the intervention (71%). Fewer participants dropped out from the two high-protein diet groups (26.4% overall) and the two low-GI diet groups (25.6% overall) compared with the group assigned to the low-protein and high-GI diet (37.4%; p=0.02 and p=0.01 for the two comparisons, respectively). Participants had lost a mean 11.0 kg with the initial low-calorie diet. In an intention-to-treat analysis, the weight regain was 0.93 kg less in the high-protein groups than in the low-protein groups (p=0.003) and 0.95 kg less in the low-GI diet groups than in the high-GI diet groups (p=0.003). Only the low-protein, high-GI group gained a significant amount of weight over the 6 months (1.67 kg, p<0.01). When analyzed separately by center, the high-protein groups gained 2.7 kg less body weight than the low-protein groups (p<0.001) in the shop centers, whereas the difference between protein diets was only 0.54 kg (p=0.13) in the instruction centers. Conversely, there was only a 0.48 kg difference between high- and low-GI diets (p=0.48) in shop centers, whereas there was a 1.03 kg weight gain difference (p=0.004) in instruction centers.
This remarkably successful study has shown that a family-focused intervention can achieve an 11 kg weight loss and maintain nearly all of it for 6 months. This study has confirmed previous shorter and smaller studies that show that increasing protein and lowering GI increases weight loss or weight maintenance by about 0.6-1 kg for each intervention and that the two changes are entirely additive.
This study has also shown that advising people to increase their protein intake is relatively ineffective in achieving an increase in protein and enhancing weight maintenance, whereas providing high-protein foods is effective as has been previously shown. The reverse was shown with GI: providing low-GI foods was ineffective relative to high-GI foods, while asking people to choose low-GI foods enhanced dietary compliance. This finding suggests the GI of foods per se has no impact on weight maintenance which differs from the authors’ conclusions. In their discussion, the authors confuse GI and glycemic load (GL). There is better evidence that lowering GL by lowering carbohydrate, increasing protein and lowering GI has more of an effect on weight than lowering GI without changing the carbohydrate amount.
Whether protein or GI would have an influence in a non-family based setting and in a clinic population seen much less frequently (i.e., a maximum of two to three times over 6 months) is unknown. The most important question still to be answered is what would happen in the longer term (e.g., over subsequent years), as 6 months is still very short for a lifetime obesity problem.
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Evid Based Med. 2011;16(4)