ProteinNEW2026-09

A self-selected vegan diet reduces skeletal muscle mass in healthy older adults: a randomized controlled trial.

Domić Jacintha, Grootswagers Pol, Pinckaers Philippe Jm, Melchers Max et al. — The American journal of clinical nutrition

Summary

A recent study found that healthy older adults who followed a self-selected vegan diet for 12 weeks experienced a reduction in muscle mass and lower protein intake compared to those eating an omnivorous diet. However, combining the vegan diet with resistance exercise helped prevent this muscle loss. This suggests that careful attention to protein and physical activity is important for older adults on plant-based diets.

AI-generated summary — read the original

Key points

A self-selected vegan diet led to lower protein intake in healthy older adults.
Older adults on a vegan diet alone experienced reduced skeletal muscle mass and muscle protein synthesis.
Combining a vegan diet with resistance exercise helped prevent muscle loss in older adults.
Maintaining muscle health on a vegan diet for older adults requires attention to protein and exercise.

What the study looked at

Researchers wanted to understand how a vegan diet affects muscle health in older adults, specifically comparing it to an omnivorous diet and a vegan diet combined with resistance exercise. This 12-week randomized controlled trial involved 72 healthy individuals aged 65 and older. Participants were divided into three groups: one followed a self-selected vegan diet, another continued their usual omnivorous diet, and the third followed a vegan diet while also doing resistance exercise. Scientists measured changes in muscle mass, strength, and how quickly new muscle proteins were built. The study revealed that older adults on the vegan diet alone consumed less protein and experienced a decrease in muscle mass and muscle protein synthesis compared to the omnivore group. Importantly, the group combining a vegan diet with resistance exercise did not show the same decline in muscle mass, suggesting exercise can counteract these effects.

Dietary takeaway

For older adults considering a vegan diet, it's crucial to prioritize adequate protein intake from diverse plant-based sources and incorporate regular resistance exercise to maintain muscle mass. While this study highlights potential challenges, it also shows that strategic planning can help mitigate them. Remember, this is one study, and individual nutritional needs can vary, so consulting a healthcare professional or registered dietitian is always recommended.

Abstract

BACKGROUND: Adopting a plant-based diet may compromise protein intake and impair skeletal muscle mass in older adults. OBJECTIVES: To compare the impact of a 12-wk self-selected vegan diet with that of an omnivorous diet and a self-selected vegan diet with resistance exercise (RE) on skeletal muscle mass, strength, and muscle protein synthesis (MPS) rates in older adults. METHODS: This randomized controlled trial included 3 parallel study arms in which 72 healthy older adults aged ≥65 y were randomly assigned to follow 1) a self-selected vegan diet (VEG), 2) their habitual omnivorous diet (OMNI), or 3) a self-selected vegan diet with RE (VEG-RE). At baseline and after 12 wk, thigh muscle volume, thigh muscle fat infiltration, and body fat distribution were assessed using magnetic resonance imaging, appendicular lean mass with dual x-ray absorptiometry, and muscle strength via Biodex. MPS rates were assessed during the first 10 d using a deuterium oxide protocol. Other outcome measures were body mass, dietary intake, and physical activity. Linear mixed models were applied to test differences between VEG and the other groups. Results are presented as estimated marginal mean or change in estimated marginal mean [95% confidence interval (CI)]. RESULTS: VEG reduced protein intake with ‒27.7 g/d (95% CI: ‒37.3, ‒18.2 g/d), ‒22.0 g/d (95% CI: ‒31.7, ‒12.4 g/d), and ‒19.3 g/d (95% CI: ‒29.2, ‒9.37 g/d) in weeks 1, 6, and 12 (all P < 0.0001 compared with baseline), which was similar to the decrease in VEG-RE (P > 0.05), but different from OMNI (P < 0.0001), in which protein intake did not change. Thigh muscle volume and appendicular lean mass significantly reduced in VEG [‒0.61 L (95% CI: ‒0.72, ‒0.50 L); ‒1.15 kg (95% CI: ‒1.46, ‒0.85 kg)] compared to OMNI [‒0.01 L (95% CI: ‒0.11, 0.09 L); +0.05 kg (95% CI: ‒0.23, 0.32 kg); both P < 0.0001] and VEG-RE [‒0.35 L (95% CI: ‒0.47, ‒0.24 L), P = 0.0038; ‒0.62 kg (95% CI: ‒0.93, ‒0.32 kg), P = 0.0033]. MPS was lower in VEG [1.09 %/d (95% CI: 1.01, 1.17 %/d)] compared with OMNI [1.27 %/d (95% CI: 1.18, 1.35 %/d); P = 0.0073] and VEG-RE [1.24 %/d (95% CI: 1.16, 1.33 %/d); P = 0.0246]. CONCLUSIONS: A self-selected vegan diet reduces protein intake, skeletal muscle mass, and MPS in older adults. The negative impact of a vegan diet on skeletal muscle mass can be mitigated by RE. This trial was registered at clinicaltrials.gov as NCT05809466. (https://clinicaltrials.gov/study/NCT05809466).

View on PubMed →DOI: 10.1016/j.ajcnut.2026.101416