A scientific review suggests fermented protein foods could influence muscle strength, metabolism and recovery through communication between gut bacteria and skeletal muscle, although researchers say human evidence remains too limited to establish clear benefits.
By yourNEWS Media Newsroom
Fermented foods such as yogurt, kefir and tempeh may influence muscle health through their effects on gut bacteria, according to a scientific review examining how microorganisms and their metabolic byproducts communicate with skeletal muscle.
The review, published Sept. 25, 2026, in Communications Biology, examined laboratory experiments, animal research and human clinical trials investigating whether fermented protein foods offer benefits beyond their nutritional content.
Researchers Dominic N. Farsi, Paul D. Cotter and Orla O’Sullivan, affiliated with Ireland’s Teagasc Food Research Centre and APC Microbiome Ireland, concluded that biological evidence supports a potential relationship between intestinal microorganisms and muscle function.
However, they emphasized that convincing evidence demonstrating that fermented foods directly increase muscle mass or strength in humans remains limited.
Their analysis focused on the gut-muscle axis, a two-way communication system connecting the digestive tract, its resident microorganisms and skeletal muscle through metabolic, hormonal, immune and neurological signals.
Gut bacteria produce compounds that enter the bloodstream and may affect inflammation, blood sugar regulation, energy metabolism and muscle protein production.
Muscle activity can also influence the digestive system. Exercise changes intestinal function, immune activity and the composition of microbial communities, potentially creating a reciprocal relationship between physical activity and gut health.
The researchers identified short-chain fatty acids as particularly important chemical messengers within this system.
These compounds are produced when intestinal bacteria ferment dietary substances, especially certain fibers. They help regulate inflammation, metabolic function and cellular signaling pathways associated with muscle maintenance.
Laboratory studies have suggested that some microbial compounds can activate pathways involved in muscle growth and help protect against muscle deterioration under certain metabolic conditions.
Other research has linked specific intestinal bacteria to improved muscle strength, including experiments in mice showing changes in grip strength and muscle fiber characteristics following bacterial supplementation.
Nevertheless, animal and laboratory findings cannot establish that similar effects will occur in people consuming ordinary fermented foods.
The question is particularly relevant to sarcopenia, the progressive decline in muscle mass and function associated with aging.
Sarcopenia can contribute to weakness, falls, reduced mobility and loss of independence. Maintaining skeletal muscle also plays an important role in regulating blood glucose and overall metabolic health.
Adequate protein consumption and resistance exercise remain the principal evidence-supported strategies for maintaining muscle as people age.
Researchers are investigating whether modifications to the gut microbiome could provide additional benefits, particularly because older adults often experience a diminished muscle-building response to dietary protein.
Fermentation may offer several possible advantages.
During food production, microorganisms transform proteins, alter amino acid availability and generate biologically active peptides and other compounds.
Some fermented foods also contain live microorganisms that can temporarily interact with intestinal bacteria.
The review suggests these characteristics may influence protein digestion, nutrient absorption and inflammatory processes in ways that potentially support muscle function.
However, the available human trials have produced mixed results.
One study involving 48 middle-aged Korean men compared fermented whey protein with conventional whey protein during an eight-week exercise program.
Participants consuming fermented whey showed greater improvements in balance, but researchers found no meaningful differences between groups in grip strength or back strength.
Another trial examined a drink containing compounds produced by kefir-associated bacteria in 53 healthy adults averaging approximately 55 years of age.
After 12 weeks, participants receiving the experimental drink demonstrated improved grip strength within their group, but the difference compared with placebo was not statistically convincing.
The formulation also differed from ordinary kefir, limiting its relevance to fermented dairy products sold in supermarkets.
A third investigation involved 18 healthy young men who consumed fermented or regular milk around an intense exercise session.
Those receiving fermented milk reported less muscle soreness afterward, suggesting a possible effect on perceived recovery. However, the study examined only a single exercise session and did not establish long-term improvements in muscle mass or athletic performance.
Taken together, the trials suggest possible benefits but do not demonstrate that fermented protein foods consistently improve muscle strength or growth.
The researchers also distinguished fermented foods from probiotic supplements.
Probiotics typically contain measured quantities of specific microorganisms, making their effects easier to evaluate in controlled clinical trials.
Some studies involving probiotic supplementation have reported improvements in muscle strength and modest increases in muscle mass, particularly among older adults.
Fermented foods, by contrast, contain varying combinations of microorganisms, peptides and metabolic compounds depending on their ingredients, production methods and storage conditions.
Their effects may therefore differ considerably between products, even within the same food category.
The evidence is further limited by the small number of controlled human trials, differences in participants’ ages and diets, and inconsistent methods for measuring muscle function.
Most investigations have focused on fermented dairy products, leaving relatively little direct evidence concerning plant-based fermented protein sources such as tempeh.
The review also acknowledged the difficulty of separating the effects of fermentation from those of protein intake and exercise, particularly when researchers combine these interventions.
The authors called for larger clinical trials involving older adults, athletes and people recovering from injury or illness.
Future studies should compare fermented and nonfermented protein foods while directly measuring muscle protein synthesis, muscle mass, physical performance and changes in intestinal microorganisms.
The research was supported in part by a European Union research fellowship. The publication also disclosed that Cotter’s laboratory has received research funding from several food and nutrition companies, including Danone, FrieslandCampina and PepsiCo.
The findings do not establish fermented foods as a treatment for age-related muscle loss or a substitute for regular exercise and sufficient dietary protein.
Instead, they suggest that fermentation may influence how protein-rich foods interact with the digestive system, potentially affecting biological processes important to maintaining muscle.
For researchers, the next step is determining whether those mechanisms produce meaningful improvements in human strength, mobility and recovery under controlled conditions.
Until then, the gut-muscle connection remains a promising area of nutritional research rather than a proven strategy for building or preserving muscle.
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