Effects of protein intake and gender on body composition changes: a randomized clinical weight loss trial

ABSTRACT: Limited data on sex differences in body composition changes in response to higher protein diets (PRO) compared to higher carbohydrate diets (CARB) suggest that a PRO diet helps preserve lean mass (LM) in women more so than in men. OBJECTIVE: To compare male and female body composition responses to weight loss diets differing in macronutrient content. DESIGN: Twelve month randomized clinical trial with 4mo of weight loss and 8mo weight maintenance. SUBJECTS: Overweight (N = 130; 58 male (M), 72 female (F); BMI = 32.5 ± 0.5 kg/m2) middle-aged subjects were randomized to energy-restricted (deficit ~500 kcal/d) diets providing protein at 1.6 g.kg-1.d-1 (PRO) or 0.8 g.kg-1.d-1 (CARB). LM and fat mass (FM) were measured using dual X-ray absorptiometry. Body composition outcomes were tested in a repeated measures ANOVA controlling for sex, diet, time and their two- and three-way interactions at 0, 4, 8 and 12mo. RESULTS: When expressed as percent change from baseline, males and females lost similar amounts of weight at 12mo (M:-11.2 ± 7.1 %, F:-9.9 ± 6.0 %), as did diet groups (PRO:-10.7 ± 6.8 %, CARB:-10.1 ± 6.2 %), with no interaction of gender and diet. A similar pattern emerged for fat mass and lean mass, however percent body fat was significantly influenced by both gender (M:-18.0 ± 12.8 %, F:-7.3 ± 8.1 %, p < 0.05) and diet (PRO:-14.3 ± 11.8 %, CARB:-9.3 ± 11.1 %, p < 0.05), with no gender-diet interaction. Compared to women, men carried an extra 7.0 ± 0.9 % of their total body fat in the trunk (P < 0.01) at baseline, and reduced trunk fat during weight loss more than women (M:-3.0 ± 0.5 %, F:-1.8 ± 0.3 %, p < 0.05). Conversely, women carried 7.2 ± 0.9 % more total body fat in the legs, but loss of total body fat in legs was similar in men and women. CONCLUSION: PRO was more effective in reducing percent body fat vs. CARB over 12mo weight loss and maintenance. Men lost percent total body fat and trunk fat more effectively than women. No interactive effects of protein intake and gender are evident.