Differences in the gut microbiome by physical activity and BMI among colorectal cancer patients
To better understand the role of the gut microbiome in colorectal cancer (CRC) development, a new study investigated associations between physical activity, body mass index (BMI), gut microbiome diversity and different abundances of gut microbes among CRC patients. The study, published in the American Journal of Cancer Research, showed that regular exercise had a positive impact on promoting a healthy gut microbiome while also reducing inflammation in the body. The researchers found that patients who are more active have more diverse microbiomes and lower amounts of colorectal cancer promoting bacteria and higher amounts of bacteria that protect against colorectal cancer.
What is the gut microbiome?
The gut microbiome is the totality of microorganisms that live in our gut, or intestines. The microbiome, while mainly comprising bacteria, is also made up of fungi, viruses, protozoa, and other microscopic organisms. Based on the broad evidence about the gut microbiome, having diverse populations of bacteria is an important characteristic of a healthy microbiome.
What is BMI?
Body mass index (BMI) is calculated using a person’s weight in kilograms or pounds divided by the square of their height in meters or feet. While BMI can give a rough estimate of body fatness, it is not a direct measure for body fat content or total health of the individual.
|18.5 – 24.9||Healthy Weight|
|25.0 – 29.9||Overweight|
|30.0 and Above||Obesity|
Association between physical activity, BMI and cancer prevention and control
Both physical activity and BMI have emerged as predictive factors in cancer prevention and control, where increased physical activity levels throughout the cancer care continuum may reduce the risk of death by up to 38% in CRC survivors. With BMI, there is not such a clear and linear relationship with CRC survival, with superior survival outcomes seen for overweight and class 1 obese patients compared to other BMI categories such as underweight, or normal weight.
The study aimed to understand how the gut microbiome may function as an underlying mechanism that influences the physical activity / BMI – colorectal cancer link.
179 patients with CRC (stages 1-4) were included in the study. Stool samples were taken pre-surgery and physical activity during the year before their diagnosis was assessed by questionnaire and participants were classified as being active vs. inactive based on the provided guidelines. BMI at this time was calculated based on the patients’ medical records.
The diversity of the lower gut microbiome was observed and compared among patients classified as inactive vs. active, obese vs. normal weight. The researchers found that the gut microbiomes of active and normal weight patients are more diverse compared to those of inactive patients.
These findings provide evidence for an association between higher physical activity levels and greater gut microbiome diversity, with quantities of microbial subtypes varying among CRC patients. The study data showed that overweight and obese patients had lower microbial diversity compared to normal weight and active patients, supporting existing evidence that indicates the negative impact of BMI on the gut microbiome among CRC patients. This highlights the gut microbiome as an interface of the obesity-colorectal cancer link.
Furthermore, the study findings show that increased physical activity may counteract obesity-induced metabolic effects and dysbiosis of the gut microbiome in CRC patients.
Take home message
Findings from a recent study showed that regular physical activity may help to offset imbalances to the gut microbiome that occur as a result of obesity, reduce BMI and inflammation and may extend the survival of patients with colorectal cancer.
 Meyerhardt JA, Giovannucci EL, Holmes MD, Chan AT, Chan JA, Colditz GA, Fuchs CS. Physical activity and survival after colorectal cancer diagnosis. J. Clin. Oncol. 2006;24:3527–3534.
 Brown JC, Meyerhardt JA. Obesity and energy balance in GI cancer. J. Clin. Oncol. 2016;34:4217–4224.