This randomised trial assigned 72 healthy adults aged 65 or over to a self-selected vegan diet, their habitual omnivorous diet, or a self-selected vegan diet plus resistance exercise, for 12 weeks, with muscle measured by MRI and DXA.
Left to choose their own vegan meals, participants cut protein intake by roughly 20–28 g/day. Over 12 weeks the vegan group lost thigh muscle volume (-0.61 L) and appendicular lean mass (-1.15 kg), while omnivores lost essentially none (both differences P<0.0001); muscle protein synthesis was also lower. Adding resistance exercise roughly halved the muscle loss (lean mass -0.62 kg).
The message is not that older adults should avoid plant-based eating, but that doing it casually is risky for muscle. A vegan diet in later life needs deliberate attention to protein quantity and quality and, ideally, resistance training alongside — otherwise it accelerates the sarcopenia these patients are already at risk of.
- Self-selected vegan diet cut protein intake by ~20–28 g/day
- Lost thigh muscle volume (-0.61 L) and lean mass (-1.15 kg) over 12 weeks; omnivores lost none
- Resistance exercise roughly halved the muscle loss
- Counsel deliberate protein targets and resistance training before an older patient goes vegan
The statistics, in plain English
A loss of 1.15 kg of appendicular lean mass in 12 weeks, with a confidence interval well away from zero and P<0.0001, is both statistically clear and clinically meaningful in older adults, for whom muscle loss drives falls and dependence. That resistance exercise cut the loss roughly in half shows the effect is about protein and stimulus, not something intrinsic to plant foods.
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