Plant protein held its own against animal protein in older adults

Muscle mass, strength and physical function all decline with age, and holding onto them is central to staying independent in later life. Protein intake alongside exercise is the standard recommendation, but the supporting evidence has overwhelmingly come from animal proteins. Plant proteins have historically been considered second-rate because of lower digestibility and incomplete amino acid profiles, yet newer plant-based proteins and products may have overcome those limitations. This review asked whether plant protein can hold its own in adults aged 60 and over, and whether adding exercise improves its effectiveness.

The reviewers searched several databases for randomised controlled trials published up to January 2023 that tested a plant-based protein intervention in adults aged 60 or over and assessed body composition, strength or physical function. Thirteen trials qualified, and every one used soy protein, at daily doses ranging from 0.6 to 60 g, with interventions lasting from 12 weeks to 1 year. Comparison groups included no intervention, exercise alone, animal protein, and animal protein combined with exercise, and the results were synthesised in both a narrative summary and a meta-analysis.

Soy protein interventions produced positive effects on muscle mass over time, but those gains were not significantly different from the comparison groups, including groups taking animal protein with or without exercise. Effects on strength and physical function were limited across the trials. In the meta-analysis, plant-protein interventions were comparable to controls on all outcomes measured. The headline result is parity: soy protein neither outperformed nor fell behind the alternatives it was tested against.

The long-standing assumption has been that plant proteins are an inferior tool for preserving ageing muscle. These pooled results complicate that view, since soy kept pace with animal protein across body composition, strength and function in this population. The evidence base is narrow, though: all 13 trials used soy, so nothing here speaks to other plant sources, and the authors call for further investigation of plant protein as an anabolic stimulus in older adults. Why strength and function moved so little across all interventions also remains an open question.

For older adults who prefer plant-based eating, or anyone drifting that way, this is a reason to think soy protein is not an automatic downgrade for maintaining muscle. Across the pooled trials it performed comparably to animal protein and to other approaches on every outcome measured. The limited movement in strength and function under all the interventions is a reminder that no protein source is a shortcut, and that the source may matter less than commonly assumed.