In recent years, awareness has increased about the prognostic value of skeletal muscle changes in chronic diseases, and a multimodal approach is considered the best option for treating muscle loss. In this context, the intestinal microbiota is shaping up as a new and promising objective.

    The gut microbiota, located in the gastrointestinal tract, the primary site of the human microbiota, is a key regulator of host metabolism and immunity. The understanding that the intestinal microbiota influences health also aroused interest in the mechanisms underlying this interference and in the therapeutic opportunities that may result from them. Many of the effects that microbiota has on host physiology are mediated by metabolites produced by these microorganisms or derived from the transformation of the environment.

    Evidence on the relationship between the microbiota-intestinal muscle axis has been evidenced in studies with animal and human models, as well as in vitro studies. Research on germ-free mice showed a 7% decrease in lean body mass. Depletion or reduction of the intestinal microbiota (through treatment with broad-spectrum antibiotics) was also later associated with alterations in muscle function and muscle metabolism.

    A study on the transfer of fecal microbiota from older people with high functional capacity, due to musculature, to germ-free mice showed an increase in muscle strength in these mice compared to mice colonized with adult fecal matter with low functional capacity associated with low musculature.

    Still, others research has shown that administering prebiotics (inulin and fructooligosaccharides) improves grip strength in frail older people; and administering probiotics for 4 weeks before a half marathon reduces muscle damage and oxidative stress associated with the test, without affecting exercise capacity.

    The recent expansion of the scope of studies made it possible to analyze the mechanisms by which the intestinal microbiota affects muscle physiology, the main metabolites studied in this context being short-chain fatty acids (SCFAs).

    The way in which SCFAs can affect muscle physiology has been extensively reviewed. In summary, SCFAs have been shown to influence lipid, carbohydrate and protein metabolism in skeletal muscle tissues, both in vitro and in vivo. In addition, SCFAs have the potential to increase skeletal muscle mass retention, blood flow and insulin sensitivity, and to preserve an oxidative phenotype.

    For example, research has reported that butyrate prevents many aging-related muscle changes. Chronic administration of butyrate to elderly mice protected them against muscle atrophy in hindlimb muscles, prevented intramuscular fat accumulation, increased markers of mitochondrial biogenesis, and reduced markers of oxidative stress and apoptosis.

    There is great scientific interest in promoting the production of SCFAs in humans to improve muscle physiology. However, for now, associations have only been reported in observational cohorts and there are no intervention trials to demonstrate the impact of SCFAs derived from intestinal microbiota on muscle physiology in human beings.

    In this regard, it can be seen that it is extremely important, for the recovery and/or maintenance of muscle health, to take care of intestinal integrity. Therefore, clinical protocols related to the use of probiotics, glutamine and prebiotic fibers must be implemented according to the individuality of each patient.

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References:

Lefevre C, Bindels LB. Role of the intestinal microbiome in the physiology and pathophysiology of skeletal muscle. Curr Osteoporos Rep. 2022 December 2022; 20 (6) :422-432.

Han DS, WuWk, Liu PY, Yang YT, Hsu HC, Kuo CH, Wu MS, Wang TG. Differences in the intestinal microbiome and reduction of fecal butyrate in elderly people with low skeletal muscle mass. Clin Nut. 2022 July 22; 41 (7): 1491-1500.

Lv WQ, Lin X, Shen H, Liu HM, Qiu X, Li BY, Shen WD, Ge CL, Lv FY, Shen J, Xiao HM, Deng HW. The human gut microbiome affects skeletal muscle mass through the intestinal microbial synthesis of short-chain fatty acid butyrate in healthy menopausal women. Muscle with cachexia and sarcopenia. 12 (6): 1860-1870 December 2021.

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