Effects of 4 weight-loss diets differing in fat, protein, and carbohydrate on fat mass, lean mass, visceral adipose tissue, and hepatic fat: results from the POUNDS LOST trial

Abstract

Background: Weight loss reduces body fat and lean mass, but whether these changes are influenced by macronutrient composition of the diet is unclear.

Objective: We determined whether energy-reduced diets that emphasize fat, protein, or carbohydrate differentially reduce total, visceral, or hepatic fat or preserve lean mass.

Design: In a subset of participants in a randomized trial of 4 weight-loss diets, body fat and lean mass (n = 424; by using dual-energy X-ray absorptiometry) and abdominal and hepatic fat (n = 165; by using computed tomography) were measured after 6 mo and 2 y. Changes from baseline were compared between assigned amounts of protein (25% compared with 15%) and fat (40% compared with 20%) and across 4 carbohydrate amounts (35% through 65%).

Results: At 6 mo, participants lost a mean (±SEM) of 4.2 ± 0.3 kg (12.4%) fat and 2.1 ± 0.3 kg (3.5%) lean mass (both P < 0.0001 compared with baseline values), with no differences between 25% and 15% protein (P ≥ 0.10), 40% and 20% fat (P ≥ 0.34), or 65% and 35% carbohydrate (P ≥ 0.27). Participants lost 2.3 ± 0.2 kg (13.8%) abdominal fat: 1.5 ± 0.2 kg (13.6%) subcutaneous fat and 0.9 ± 0.1 kg (16.1%) visceral fat (all P < 0.0001 compared with baseline values), with no differences between the diets (P ≥ 0.29). Women lost more visceral fat than did men relative to total-body fat loss. Participants regained ~40% of these losses by 2 y, with no differences between diets (P ≥ 0.23). Weight loss reduced hepatic fat, but there were no differences between groups (P ≥ 0.28). Dietary goals were not fully met; self-reported contrasts were closer to 2% protein, 8% fat, and 14% carbohydrate at 6 mo and 1%, 7%, and 10%, respectively, at 2 y.

Conclusion: Participants lost more fat than lean mass after consumption of all diets, with no differences in changes in body composition, abdominal fat, or hepatic fat between assigned macronutrient amounts. This trial was registered at clinicaltrials.gov as NCT00072995.

FIGURE 1.

Mean (±SEM) changes from baseline to 6 mo in lean and fat mass (n = 424; intention-to-treat analysis) expressed by using generalized linear model ANOVA models that included the main effect of diet with baseline, age, sex, and site as covariates. P values assessed the significance of the difference between the change on the 2 assigned amounts of each macronutrient (high protein = 25%, average protein = 15%; high fat = 40%, low fat = 20%; and highest carbohydrate = 65%, lowest carbohydrate = 35%), adjusted for multiple comparisons by using the Tukey-Kramer method.

FIGURE 2.

Mean (±SEM) changes from baseline to 6 mo in visceral and subcutaneous abdominal fat (n = 165; intention-to-treat analysis) expressed by using generalized linear model ANOVA models that included the main effect of diet with baseline, age, sex, and site as covariates. P values assessed the significance of the difference between the change on the 2 assigned amounts of each macronutrient (high protein = 25%, average protein = 15%; high fat = 40%, low fat = 20%; and highest carbohydrate = 65%, lowest carbohydrate = 35%), adjusted for multiple comparisons using the Tukey-Kramer method.

FIGURE 3.

Linear regression of the ratio of the change in VAT to the change in FM compared with the ratio of initial VAT to FM across all 4 diets at 6 mo (n = 101) and at 2 y (n = 58) in men (open circles) and in women (filled circles). The analysis included only participants who lost both visceral adipose tissue and body fat (ie, ΔVAT and ΔFM <0) and who lost ≥5 kg body weight. The line corresponds to the best-fit allometric relation to the weight-loss data, with k = 1.19 ± 0.04 (r² = 0.47) at 6 mo and k = 1.27 ± 0.05 (r² = 0.61) at 2 y. FM, total fat mass; VAT, visceral fat mass.

FIGURE 4.

Mean (±SEM) changes from baseline to 6 mo in hepatic fat (n = 194; intention-to-treat analysis). Increases in hepatic density were produced by decreases in hepatic fat. Hepatic density was defined by the difference between liver and spleen density (Hounsfield units). Data were expressed by using generalized linear model ANOVA models that included main effect of diet with baseline, age, sex, and site as covariates. P values assessed the significance of the difference between the change on the 2 assigned amounts of each macronutrient (high protein = 25%, average protein = 15%; high fat = 40%, low fat = 20%; and highest carbohydrate = 65%, lowest carbohydrate = 35%), adjusted for multiple comparisons by using the Tukey-Kramer method. Diff, difference.