# The Effects of Soy Protein–Rich Meals on Muscle Health of Older Adults Are Linked to Gut Microbiome Modifications

## TL;DR

A soy protein-rich diet may improve muscle health in older adults by changing gut bacteria, suggesting a link between gut health and muscle function.

## Contribution

This study shows that soy protein improves muscle health in older adults by modifying gut microbiota, supporting the gut–muscle axis hypothesis.

## Key findings

- Participants on a soy protein-rich diet preserved calf circumference, while the control group's decreased.
- The intervention increased SCFA-producing bacteria like Roseburia faecis and decreased harmful species like Alistipes putredinis.
- Functional analysis showed reduced inflammatory pathways and increased vitamin biosynthesis in the intervention group.

## Abstract

Sarcopenia is characterized by accelerated muscle mass and function loss in older adults. The role of nutritional interventions in sarcopenia is uncertain. This study investigates whether a soy protein–rich diet can enhance muscle health in older adults via gut microbiota changes.

A 12‐week randomized controlled trial was conducted with 84 older adults from a long‐term care facility. Participants in the intervention group consumed three daily meals containing 10 g of soy protein (totalling 30 g/day), while the control group maintained their usual diets. Faecal samples from 53 participants were collected at Weeks 0, 6 and 12. We assessed changes in muscle function, gut microbiota composition and faecal short‐chain fatty acids (SCFA).

The intervention group showed preserved calf circumference, while the control group experienced a decrease (W12‐W0: Intervention, 0.56 ± 0.22 cm; Control, −0.91 ± 0.26 cm, p
(interaction) < 0.001). Metagenomic analysis revealed significant alterations in gut microbiota among intervention participants who showed improvement in muscle performance parameters. The intervention increased SCFA‐producing bacteria (
Roseburia faecis
, Intervention: 0.42 ± 0.21%, Control: −0.06 ± 0.16, p
(interaction) < 0.05;
Agathobaculum butyriciproducens
, Intervention: 0.02 ± 0.007%, p
(time) < 0.01, Control: −0.04 ± 0.01) and decreased species associated with poorer muscle outcomes (
Alistipes putredinis
, Intervention: −0.88 ± 0.40%, Control: 0.62 ± 0.63, p
(interaction) < 0.05; Eubacterium_sp_CAG_38, Intervention: −0.64 ± 0.28%, Control: 0.10 ± 0.22, p
(interaction) < 0.05). Functional pathway analysis showed enrichment of anaerobic amino acid degradation pathways and vitamin biosynthesis, with depletion of inflammatory pathways, particularly lipopolysaccharide biosynthesis. Microbiome phenotype prediction revealed a decrease in aerobic bacteria abundance in the intervention group (W12‐W0, Intervention: −0.004 ± 0.002; Control: 0.001 ± 0.001, p
(interaction) < 0.05). Interaction (group × time) for SCFA was not statistically significant; within‐group increases at Week 6 were observed in only the intervention group (butyric acid, Intervention: 0.74 ± 0.34 mg/g, p
(time) < 0.05, Control: 0.12 ± 0.43 mg/g; isobutyric acid, Intervention: 0.14 ± 0.08 mg/g, p
(time) < 0.05, Control: 0.08 ± 0.10 mg/g; isovaleric acid, Intervention: 0.27 ± 0.14 mg/g, p
(time) < 0.05; Control: 0.16 ± 0.20 mg/g), with partial reversal by Week 12. These changes, positively correlated with improved muscle function parameters, suggest intervention benefits on gut health and muscle function.

A soy protein–rich intervention improved muscle health in older adults through beneficial gut microbiota. These findings support the gut–muscle axis hypothesis and suggest dietary soy protein may alleviate sarcopenia by promoting a healthier gut microbiome.