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Newer research is investigating the link between exercise and gut bacteria in people with cancer. Justin Paget/Getty Images
  • Several factors may contribute to the development of colorectal cancer, and research suggests that gut microbiota may also play a role.
  • New research has found that regular exercise positively impacts gut microbiome diversity in people with colorectal cancer.
  • According to the study, this is the first research to examine the associations between exercise and gut biome diversity in people with cancer.

Statistics suggest that, excluding skin cancers, colorectal cancer is the third leading cause of cancer-related deaths in the United States.

Although scientists aren’t sure what causes colorectal cancer, contributing risk factors may include a lack of regular physical activity, a diet low in fiber and high in fat, and obesity.

Moreover, a 2018 study reports that altered gut microbiota associated with chronic inflammation has been observed in pancreas, gastric, colon, liver, breast, and prostate cancers.

Factors that impact the gut microbiota include diet, age, and antibiotic use. A 2021 study also suggested that moderate endurance exercise may positively affect gut microbial diversity, reduce inflammation, and improve body composition.

Yet, it is unknown how physical activity impacts the gut microbiome of people with cancer.

Now, a new study examining the relationship between physical activity and the gut microbiome in people with colorectal cancer has found that regular exercise is associated with higher levels of gut biome diversity — even in people with obesity or those who are overweight.

According to the study, this research is the first to examine links between exercise and the microbiome of people with cancer.

The paper appears in the American Journal of Cancer Research.

Building on their previous August and October 2022 studies, the research team sought to examine the associations between physical activity, BMI, and gut microbiome diversity among people with colorectal cancer.

The team collected data from 179 people enrolled in the ColoCare Study between October 2010 and March 2018. The ColoCare Study is an international cohort of people recently diagnosed with stage I-IV colorectal cancer.

Data collected included pre-surgery stool samples and BMI measurements from medical records. The scientists then performed 16S rRNA gene sequencing on the stool samples to determine the participant’s microbiome diversity.

In addition, the scientists used the BMI measurements to categorize participants into three groups:

  • Healthy weight: BMI of ≥18.5 and <25 kg/m2
  • Overweight: BMI of ≥25 and <30 kg/m2
  • Obese: BMI of ≥30 kg/m2

The participants also completed an adapted version of the International Physical Activity Questionnaire (IPAQ) to determine their level of physical activity during the year before they were diagnosed with colorectal cancer. The scientists calculated the duration and hours of physical activity per week in metabolic equivalent tasks hours per week (MET hrs/wk).

Using these calculations, the researchers classified participants as inactive if their physical activity was less than 8.75 MET hours per week and active if their activity was 8.75 MET hours per week or more.

The scientists noted that having a MET of at least 8.75 meets the U.S. Department of Health and Human Services guidelines recommending at least 150 minutes (2.5 hours) per week of moderate activity. This guideline may also apply to cancer survivors.

Then, the research team grouped participants into four physical activity level/BMI categories:

  • Healthy weight/active: 26 participants
  • Healthy weight/inactive: 33 participants
  • Overweight/obese/active: 46 participants
  • Overweight/obese/inactive: 74 participants

After compiling the data, the scientist found:

  • The gut microbiome of active and healthy-weight participants was more diverse than that of inactive participants.
  • Participants with obesity had lower alpha diversity than those classified as healthy weight.
  • The gut microbiome of healthy weight/active participants was more diverse than those categorized as overweight/obese/inactive.
  • Faecalibacterium—a beneficial bacteria—was enriched in active participants regardless of BMI.
  • Overall, lower gut microbial diversity was observed among inactive, obese, and overweight/ obese/inactive participants.

Moreover, gut biome diversity was not statistically significantly associated with the participant’s stage at diagnosis, tumor site, and neoadjuvant treatments. Also, the researchers observed no differences in individual or combined physical activity and BMI groups for those with rectal cancer.

The research team suggests that this evidence supports an association between higher physical activity levels and greater gut microbiome diversity and abundance among people with colorectal cancer — even those with obesity.

Although these findings show an association between moderate exercise and increased gut biome diversity, limitations to the study include:

  • The study was cross-sectional and did not follow people up. It, therefore, cannot establish cause and effect.
  • All the patients had bowel cancer, and there was no comparison healthy group.
  • The rRNA gene sequencing used in the study may lack accuracy in some respects.
  • This study used participants diagnosed with colorectal cancer. Therefore, it is unclear if the results would be the same in cancer-free individuals.
  • Physical activity was self-reported, which may result in the misclassification of active vs. inactive participants.

Dr. Gabriela Rodríguez Ruiz, a board certified bariatric surgeon at VIDA Wellness and Beauty, told Medical News Today:

“The gut biome contains a community of billions of bacterial cells that produce compounds called short-chain fatty acids (SCFAs) during the fermentation process. These SCFAs act as signaling molecules that tell the cells in your intestinal lining not to release pro-inflammatory cytokines, which are associated with the development of autoimmune diseases like rheumatoid arthritis and inflammatory bowel disease.”

Dr. Rodríguez Ruiz explained that the disruption of the gut microbiota — also known as gut dysbiosis — may be a significant factor in the development of inflammatory diseases.

Dr. Bill Rawls, author of The Cellular Wellness Solution and Unlocking Lyme and co-founder and medical director of Vital Plan, further explained gut dysbiosis to MNT:

“Dysbiosis is when the balance of bacteria in the gut shifts from [healthy] flora to bacteria that have the potential to be pathogens. […]. If [healthy] flora are suppressed, pathogens can damage the gut lining, causing digestive dysfunction, but also secrete substances that affect brain functions and cellular health throughout the body.”

Dr. Rawls said that poor diet and chronic stress are primary factors in gut dysbiosis. High consumption of carbohydrate-dense foods and animal fat are also factors.

“Another common factor [for gut dybiosis] is excessive and prolonged use of antibiotics. Antibiotics suppress [healthy] flora and allow pathogens to flourish.”
— Dr. Bill Rawls

“In conventional medicine, we treat chronic inflammation by artificially blocking the processes of inflammation. While this can decrease the damage associated with the inflammatory process, it doesn’t address the underlying causes of cellular stress,” Dr. Rawls explained.

“If the factors causing cellular stress are not addressed, healing is impaired, and chronic illness progresses,” he noted.

“The first step is to make dietary changes to include more probiotic-rich foods in your diet, such as fermented vegetables like kimchi or sauerkraut, kefir, yogurt, and other cultured dairy products.”
— Dr. Gabriela Rodríguez Ruiz

Dr. Rodríguez Ruiz suggested that probiotics in supplement form may also help.

“Additionally, eating a diet high in fruits and vegetables is important to support diversity and health of your microbiome, as these foods contain vitamins and minerals essential for good gut health,” she told MNT.

“Other lifestyle practices, such as getting enough sleep and reducing stress, can also help improve your gut biome’s diversity and health. Regular exercise can also help to support a healthy gut by reducing inflammation and improving gut motility,” she added.

In addition, he suggested eating less meat to increase the diversity of bacteria in the gut. Although meat, especially fish and poultry, are important protein sources, Dr. Rawls believes people generally don’t need to consume large amounts.

Overall, to help promote a healthy gut biome, Dr. Rawls advised: “eat the right foods, minimize stress, and stay physically active.”