Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates

Abstract

Background: The possible advantage for weight loss of a diet that emphasizes protein, fat, or carbohydrates has not been established, and there are few studies that extend beyond 1 year.

Methods: We randomly assigned 811 overweight adults to one of four diets; the targeted percentages of energy derived from fat, protein, and carbohydrates in the four diets were 20, 15, and 65%; 20, 25, and 55%; 40, 15, and 45%; and 40, 25, and 35%. The diets consisted of similar foods and met guidelines for cardiovascular health. The participants were offered group and individual instructional sessions for 2 years. The primary outcome was the change in body weight after 2 years in two-by-two factorial comparisons of low fat versus high fat and average protein versus high protein and in the comparison of highest and lowest carbohydrate content.

Results: At 6 months, participants assigned to each diet had lost an average of 6 kg, which represented 7% of their initial weight; they began to regain weight after 12 months. By 2 years, weight loss remained similar in those who were assigned to a diet with 15% protein and those assigned to a diet with 25% protein (3.0 and 3.6 kg, respectively); in those assigned to a diet with 20% fat and those assigned to a diet with 40% fat (3.3 kg for both groups); and in those assigned to a diet with 65% carbohydrates and those assigned to a diet with 35% carbohydrates (2.9 and 3.4 kg, respectively) (P>0.20 for all comparisons). Among the 80% of participants who completed the trial, the average weight loss was 4 kg; 14 to 15% of the participants had a reduction of at least 10% of their initial body weight. Satiety, hunger, satisfaction with the diet, and attendance at group sessions were similar for all diets; attendance was strongly associated with weight loss (0.2 kg per session attended). The diets improved lipid-related risk factors and fasting insulin levels.

Conclusions: Reduced-calorie diets result in clinically meaningful weight loss regardless of which macronutrients they emphasize. (ClinicalTrials.gov number, NCT00072995.)

2009 Massachusetts Medical Society

Figures

Figure 1. Mean Change in Body Weight and Waist Circumference from Baseline to 2 Years According to Dietary Macronutrient Content

Solid bars represent high-protein, high-fat, or highest-carbohydrate diets. Open bars represent average-protein, low-fat, or lowest-carbohydrate diets. T bars indicate standard errors. Panels A and C show the change in body weight and the change in waist circumference, respectively, for all participants who were randomly assigned to a diet (a total of 811); missing data were imputed. A total of 403 participants were assigned to a high-protein diet and 408 to an average-protein diet, 405 were assigned to a high-fat diet and 406 to a low-fat diet, and 204 were assigned to the highest-carbohydrate diet and 201 to the lowest-carbohydrate diet. Panel B shows the change in body weight for the 645 participants who provided measurements at 2 years. Of these participants, 325 were assigned to a high-protein diet and 320 to an average-protein diet, 319 were assigned to a high-fat diet and 326 to a low-fat diet, and 169 were assigned to the highest-carbohydrate diet and 168 to the lowest-carbohydrate diet. Panel D shows the change in waist circumference for the 599 participants who provided measurements at 2 years. Of these participants, 303 were assigned to a high-protein diet and 296 to an average-protein diet, 292 were assigned to a high-fat diet and 307 to a low-fat diet, and 159 were assigned to the highest-carbohydrate diet and 155 to the lowest-carbohydrate diet.

Figure 2. Mean Changes in Body Weight and Waist Circumference at Various Time Points

Panels A and C show the mean changes in body weight and waist circumference, respectively, for all participants who were assigned to a diet (a total of 811 at every time point); missing data were imputed. Panel B shows the change in body weight for participants who provided measurements at various time points: 176 to 180 participants at 6 months, 157 to 167 at 12 months, 140 to 152 at 18 months, and 151 to 168 at 2 years. Panel D shows the change in waist circumference for participants who provided measurements at various time-points: 176 to 179 at 6 months, 154 to 166 at 12 months, 135 to 148 at 18 months, and 137 to 159 at 2 years. I bars in all panels indicate standard errors.

Figure 3. Change in Body Weight from Baseline to 2 Years According to Attendance at Counseling Sessions for Weight Loss, among the 645 Participants Who Completed the Study

Panel A shows data for the low-fat, average-protein group; Panel B, for the low-fat, high-protein group; Panel C, for the high-fat, average-protein group; and Panel D, for the high-fat, high-protein group. There were no significant differences among the regression coefficients (P>0.2 for all comparisons; R2 = 0.2 for total cohort).

Figure 4. Weight Loss at 2 Years According to Adherence to Dietary Fat and Protein Goals

Intake was determined from three 24-hour diet recalls. Quintiles of fat and protein intakes are shown for the combined high-fat groups (Panel A), low-fat groups (Panel B), high-protein groups (Panel C), and average-protein groups (Panel D); there were 45 to 51 participants per quintile. Rates of attendance at group sessions (percent of total sessions attended over the 2-year period) are shown for the quintiles of fat and protein intake. I bars indicate 95% confidence intervals. P values for a trend in weight loss across quintiles are as follows: P