Fermented protein foods as modulators of the gut-muscle axis: mechanisms, evidence, and future directions.

Skeletal muscle has a profound influence on metabolic health, functional capacity and resilience across the lifespan. Beyond dietary protein and physical activity, the gut microbiome may have the capacity to impact skeletal muscle mass and function through the bidirectional network termed the gut-muscle axis (GMA). Fermented protein foods (FPFs) are protein rich matrices transformed by microbial activity that integrate modified protein structures, bioactive peptides, and live microorganisms, or components thereof, which could modulate skeletal muscle physiology. Here, we review mechanistic, preclinical and human evidence concerning the potential of FPFs to influence skeletal muscle health through GMA modulation. Although emerging human studies suggest favourable effects on metabolic regulation, inflammatory pathways and gut microbial ecology, direct evidence that FPFs impact muscle protein synthesis, muscle mass or function remains limited. Furthermore, the literature is characterised by considerable heterogeneity in interventions and outcome measures. Studies integrating comprehensive microbiome characterisation, multi-omics approaches and direct skeletal muscle phenotyping are needed to determine whether FPFs confer advantages over conventional protein foods or more established microbiome targeted strategies such as probiotic supplementation. Such studies will be essential to elucidate their role in targeted nutritional strategies for ageing, metabolic disease, muscle atrophy, and physical performance.