Weight loss and lipid changes with low-energy diets: Comparator study of milk-based versus soy-based liquid meal replacement interventions

Objectives: Soy protein intake has favorable effects on body weight and fat distribution in experimental animals but these effects have not been demonstrated in humans. To compare effects of soy- vs. milk-based meal replacements (MR) we assessed weight loss and serum lipoproteins changes for obese subjects who consumed low-energy diets (LED) including either milk-based or soy-based MR. Methods: Overweight or obese women and men (body mass indices 27-40 kg/m(2)) were randomly assigned to LED providing 1200 kcal/day, with consumption of five soy-based or two milk-based liquid MR for a 12-week weight loss trial. Serum lipoprotein measurements were obtained at baseline, 6 and 12 weeks. Results: For soy and milk MR groups, subject numbers were, respectively, 51 and 39 randomized and 30 and 22 completers. MR use averaged: soy, 3.7/day; and milk, 1.9/day. Weight losses for completers at 12 weeks were: soy MR, 9.0% of initial body weight (95% confidence intervals, 7.3-10.6%); and milk MR, 7.9% (5.8-8.8%) with no significant differences. Reductions from baseline in serum cholesterol and LDL-cholesterol values, respectively, at six weeks were significantly greater (P < 0.015) with soy MR (15.2% and 17.4%) than with milk MR (7.9% and 7.7%). Soy MR use was associated with significant reductions in serum triglycerides at 6 and 12 weeks while milk MR use was not. Conclusions: Soy MR use, as part of a low-energy diet, was associated with slightly but not significantly greater weight loss over a 12-week period than milk MR use. These observations confirm previous studies documenting the effectiveness of MR use for weight loss.