Animal protein more consistently linked to body fat loss in menopausal women than plant protein
A systematic review of 15 randomized trials in 1,161 pre- and postmenopausal women found that animal-based proteins (whey, meat, milk) showed more consistent reductions in body fat and increases in lean mass over 8–16 weeks, while plant-based proteins like soy isolate produced mixed results—though both effects were strongest when combined with calorie restriction and exercise.
Researchers searched three major databases and analyzed 15 randomized controlled trials involving 1,161 pre- and postmenopausal women to compare how animal and plant proteins affected body fat, weight, and lean mass. Eight trials tested animal-based proteins (whey, meat, and milk); seven tested plant-based protein, primarily soy isolate.
In the animal-protein trials, interventions lasting 8–16 weeks showed consistent reductions in body fat and increases in lean muscle mass, especially in longer studies. By contrast, soy protein isolate trials produced heterogeneous (inconsistent) results: short-term interventions showed minimal change, and meaningful improvements appeared mainly when combined with supervised exercise. A critical finding: when researchers isolated the effect of protein intake alone, without factoring in calorie restriction or exercise, the benefits became much less clear for both protein types. This suggests that protein type alone does not drive body composition change—the combination of adequate protein, reduced calories, and physical activity matters most. The review was conducted following PRISMA guidelines and assessed study quality using the Joanna Briggs Institute risk-of-bias tool.
The 15 trials showed animal proteins (particularly whey) reduced body fat by 8–16% in intervention windows of 8–16 weeks, with greater lean-mass gains in studies longer than 12 weeks. Soy protein results were less predictable: some trials showed no significant change in body composition, while others found benefits only when participants also exercised regularly. Mechanistically, animal proteins are higher in leucine and other amino acids that stimulate muscle protein synthesis—a pathway soy isolate lacks to the same degree. When the reviewers reanalyzed studies to remove the confounding effects of energy deficit and exercise, both protein types lost their statistical significance, underscoring that calorie balance and movement are the dominant drivers. Notably, dose and intervention duration matter: trials using 20+ grams of protein per meal over 12+ weeks showed larger effects than shorter or lower-dose protocols. This is a moderate-quality evidence base—many included trials were small and heterogeneous in design, limiting the certainty of conclusions about plant-based protein.
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Open in Cadence →References
- Dietary Intake of Animal and Plant-Based Protein on Adiposity Measurements and Body Composition in Pre- and Postmenopausal Women: A Systematic Review of Randomized Clinical Trials. — FASEB journal : official publication of the Federation of American Societies for Experimental Biology (Read the original)