Weight loss without losing muscle mass in pre-obese and obese subjects induced by a high-soy-protein diet.

OBJECTIVE: To determine change of weight, body composition, metabolic and hormonal parameters induced by different intervention protocols.

DESIGN: Randomized, controlled study including participants exhibiting a BMI between 27.5 and 35. Three different interventions containing lifestyle education (LE-G), or a substitutional diet containing a high-soy-protein low-fat diet with (SD/PA-G) or without (SD-G) a guided physical activity program.

SUBJECTS: A total of 90 subjects (mean weight 89.9 kg; mean BMI 31.5), randomly assigned to one of three treatment groups.

MEASUREMENTS: Change in body weight, fat mass and lean body mass measured with the Bod Pod device at baseline, 6 weeks and 6 months; change in metabolic and hormonal parameters.

RESULTS: In all, 83 subjects completed the 6-months study. BMI dropped highly significantly in all groups (LE-G: -2.2+/-1.43 kg/m(2); SD-G: -3.1+/-1.29 kg/m(2); SD/PA-G: -3.0+/-1.29 kg/m(2)). Subjects in the SD-G and in the SD/PA-G lost more weight during the 6-months study (-8.9+/-3.9; -8.9+/-3.9 kg) than did those in the LE-G (-6.2+/-4.2 kg), and had a greater decrease in fat mass (-8.8+/-4.27; -9.4+/-4.54 kg) than those in the LE-G (-6.6+/-4.59 kg). In contrast, no significant intraindividual or between-group changes in the fat-free mass were seen. In all groups, metabolic parameters showed an improvement in glycemic control and lipid profile.

CONCLUSIONS: Our data suggest that a high-soy-protein and low-fat diet can improve the body composition in overweight and obese people, losing fat but preserving muscle mass.