For anyone tracking both their fitness goals and environmental footprint, a large new meta-analysis delivers reassuring news: swapping your whey shake for a soy-based alternative likely won’t cost you a gram of muscle. Researchers pooled data from 18 randomized controlled trials to compare long-term outcomes of plant versus animal protein supplementation — and found no meaningful difference. If you’re already sorting through the best high protein foods for muscle support or weight management, this evidence adds an important nuance: what you eat matters more than which kingdom it came from.
What the Study Found
The systematic review and meta-analysis, published in April 2026 in Frontiers in Nutrition, covered 1,893 adults across trials lasting 6 to 31 months. Participants were supplemented with either plant-based protein (predominantly soy) or animal-based protein (all dairy-derived). On every major metric — lean body mass (SMD = 0.26), fat mass (SMD = 0.16), total body mass (SMD = 0.37), upper- and lower-body muscle strength, and cardiometabolic markers including cholesterol and triglycerides — the differences between groups were statistically non-significant. The bottom line from the authors: adequate total protein intake matters more than its source.
What This Means in Practice
The finding holds a practical message for a wide range of eaters. Vegans, vegetarians, and flexitarians who rely on soy protein, lentils, edamame, or other plant sources can achieve the same long-term body composition outcomes as those leaning on chicken, dairy, or eggs — provided they hit their daily protein target. Animal proteins still carry a slight edge in some shorter-term studies on muscle protein synthesis rates, but those differences appear to wash out over months when the overall diet is adequate. The key variable, as the research consistently shows, is total protein quantity rather than the animal-versus-plant debate.
Who Should Pay Attention
Older adults and those in resistance-training programs often assume they need specifically animal-sourced protein for maximum muscle preservation. This meta-analysis suggests that assumption may be overstated. Soy protein in particular performed on par with dairy protein across the board — a relevant finding given that soy is widely available, cost-effective, and carries its own cardiovascular benefits. For anyone building a high-protein eating plan, diversifying sources across both kingdoms remains a sensible strategy, with sufficiency of intake as the non-negotiable.