Long-Term Effects of Plant Vs. Animal Protein Supplementation on Body Composition, Muscle Strength, Physical Performance, and Cardiometabolic Risk Factors in Adults:a Systematic Review and Meta-Analysis of Randomized Controlled Trials

Why It Matters

The findings suggest nutrition guidelines and consumer choices can prioritize protein quantity over source, easing concerns for plant‑protein advocates and informing industry product strategies.

Key Takeaways

• 18 RCTs, 1,893 adults, ≥6‑month interventions.
• No significant differences in lean mass or fat mass.
• Muscle strength and performance outcomes similar across protein sources.
• Cardiometabolic markers unchanged; slight triglyceride drop in seniors.
• High heterogeneity limits certainty; further diverse trials needed.

Pulse Analysis

The debate over plant versus animal protein has long hinged on short‑term trials that often favor animal sources for muscle accretion. However, the physiological adaptations to protein intake evolve over months, and the new meta‑analysis fills a critical gap by focusing exclusively on studies lasting six months or longer. By aggregating nearly two thousand participants, the review provides a more realistic picture of how sustained supplementation influences body composition and metabolic health, moving beyond the noise of brief interventions.

Results indicate that, provided overall protein consumption meets recommended levels, the origin of the protein—whether soy isolate or whey—does not materially affect lean mass gains, fat loss, or functional strength outcomes. This parity holds across age groups and persists even when a minority of trials incorporated resistance training. The only notable nuance was a small triglyceride reduction among older adults, hinting at possible ancillary benefits of soy’s bioactive compounds. Nevertheless, the high statistical heterogeneity underscores that individual study contexts—such as dosage, baseline diet, and participant health status—still shape outcomes, warranting cautious interpretation.

For the food industry and health practitioners, the analysis signals that marketing plant‑based proteins as superior for muscle health may be overstated, while also reinforcing that plant proteins remain a viable alternative for those seeking sustainable nutrition. Future research should broaden protein sources beyond soy, target populations with low baseline protein intake, and integrate structured exercise protocols to clarify any synergistic effects. Until then, clinicians can advise patients that meeting total protein needs is the primary driver of musculoskeletal and cardiometabolic benefits, regardless of whether the protein comes from a plant or animal source.