Exercise‐induced changes to the human gut microbiota and implications for colorectal cancer: a narrative review

Abstract

Physical activity is associated with reduced risks of colorectal cancer (CRC) incidence, recurrence and mortality. While these findings are consistent, the mechanism/s underlying this association remain unclear. Growing evidence supports the many ways in which differing characteristics of the gut microbiota can be tumourigenic or protective against CRC. CRC is characterised by significant dysbiosis including reduced short chain fatty acid‐producing bacteria. Recent findings suggest that exercise can modify the gut microbiota, and these changes are inverse to the changes seen with CRC; however, this exercise‐microbiota interaction is currently understudied in CRC. This review summarises parallel areas of research that are rapidly developing: The exercise–gut microbiota research and cancer–gut microbiota research and highlights the salient similarities. Preliminary evidence suggests that these areas are linked, with exercise mediating changes that promote the antitumorigenic characteristics of the gut microbiota. Future mechanistic and population‐specific studies are warranted to confirm the physiological mechanism/s by which exercise changes the gut microbiota, and the influence of the exercise–gut interaction on cancer specific outcomes in CRC.

Exercise Affects Mucosa-Associated Microbiota and Colonic Tumor Formation Induced by Azoxymethane in High-Fat-Diet-Induced Obese Mice

“…Exercise remarkably increased Akkermansia and Ruminococcaceae in mucus samples, while suppressing colon tumorigenesis, which has been reported to impede the thinning of the intestinal mucus layer caused by an HFD [22]. Furthermore, it has been reported that the abundance of Akkermansia muciniphila is inversely correlated with inflammatory biomarkers and is associated with a decreased risk of colorectal tumors [23], and that Akkermansia and Lactobacillus increase during exercise and ND [24,25]. Therefore, Akkermansia is expected to be a new probiotic [26] that induces regulatory T cells and suppresses inflammatory cytokines in chronic intestinal inflammation [27,28].…”

Exercise Training Reduces the Inflammatory Response and Promotes Intestinal Mucosa-Associated Immunity in Lynch Syndrome

“…Further, the role of gut microbiome, diet, and supplements taken by participants remain unexplored in this study. This could be critical as several studies have shown that levels of physical activity have differential effects on the intestinal microbiome that may involve in reduction of colorectal cancer risk ( 8, 49 ).…”

“…A similar beneficial association between exercise and colorectal cancer risk has been suggested in patients with LS in retrospective studies showing that physical activity of ≥35 MET-h/week decreased the risk of colorectal cancer ( 6, 7 ). However, despite the biological plausibility between exercise and reduction in colorectal cancer risk being robust, the mechanism underlying this association remains unclear with studies showing modulatory effects on the gut microbiome ( 8, 9 ), insulin growth factor signaling, and other essential pathways in colorectal cancer development to promote antitumorigenic activity ( 10, 11 ).…”

Impact of Physical Exercise on Melanoma Hallmarks: Current Status of Preclinical and Clinical Research

“…Increasing research is even focusing on the skin microbiome and its effect on the progression of melanoma 112 . In the case of other cancers, such as breast 115 and colorectal cancer 116 , exercise was documented to promote antitumor characteristics of the gut microbiome. In the case of melanoma, although there is an ongoing study aiming at examining such effects (available at https://clinicaltrials.gov/ct2/show/study/NCT04866810 ), results are still unknown.…”