Our recently published meta-analysis found that animal-based proteins confer a modest advantage in stimulating muscle protein synthesis (MPS) compared to plant-based proteins (PMID: 42055214). At first glance, this might suggest a benefit to prioritizing animal protein for muscle building.
However, the interpretation is more nuanced.
The observed advantage of animal protein was largely confined to older adults, whereas younger individuals exhibited comparable MPS responses regardless of protein source. Although speculative, this discrepancy may be related to the lower leucine content typically found in plant-based proteins. In older adults, anabolic resistance appears to elevate the leucine threshold, meaning higher per-meal leucine intake is required to effectively stimulate MPS. Importantly, this limitation can be mitigated by increasing total protein intake or fortifying plant proteins with additional leucine (PMID: 34515966).
A key limitation of the meta-analysis is that it assessed acute MPS responses rather than long-term changes in muscle mass. Nonetheless, when considered alongside recent longitudinal studies, the evidence suggests that both plant- and animal-based proteins can support similar muscular adaptations, provided total daily protein intake is sufficient (approximately 1.6 g/kg; e.g., PMID: 33599941). That said, older individuals may benefit from consuming slightly higher doses of plant protein or supplementing with leucine to optimize the anabolic response.