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Every human’s gut is filled with intestinal flora called the gut microbiome. For years, its implications in overall health have been hypothesized, but recent research has drawn more conclusive connections, even to cancer risk and prevention.
The gut microbiome has been making headlines for years now, with more and more studies emerging about its connection to every part of the body. Along with that is a growing focus on the impact an unhealthy gut environment has on our overall health.
More recently, researchers are moving beyond simple associations and toward a more concrete understanding of the relationship between the microbiota and serious and chronic diseases. Not only are our gut bugs linked to cancer via dysbiosis (imbalance in intestinal microbial communities), but certain bacteria and metabolites may actually help drive the processes behind it: inflammation, DNA damage, and even cellular changes that can begin years before a tumor forms.
The geographic relationship between gut microbiota and colon cancer isn’t a huge leap. But what is it about these small organisms living within us that has such a huge impact on disease risk and prevention?
What is the Gut Microbiome?
Our gastrointestinal (GI) tracts host trillions of microorganisms, mostly in the large intestine. It’s essentially a personalized ecosystem of bacteria, viruses, and fungi that coexist to support the immune system and protect against pathogens, aid digestion, and regulate various metabolic functions. With more than a thousand different species, the total number of microbial cells in a healthy GI tract rivals the number of human cells in the body.
Relationship to Immune System
Microbes in the gut help maintain the intestinal barrier, preventing pathogens from crossing into the bloodstream while also distinguishing between harmful invaders and normal and signaling to immune cells within the gut lining. They influence both pro-inflammatory and anti-inflammatory pathways, keeping immune responses balanced and regulated rather than overactive or suppressed.
Microbial byproducts, such as short-chain fatty acids (SCFAs), also help modulate immune cell activity, and in so doing, help control inflammation and prevent excessive immune reactions. Changes in microbiome composition have been shown to alter immune signaling, which is one of the key ways gut bacteria are linked not only to infection risk, but also to chronic inflammation and diseases like colorectal cancer.¹
Relationship to Digestion
Gut bacteria contribute directly to digestion by breaking down components of food that the human body cannot process on its own. Dietary fibers are fermented by gut microbes in the colon, and the metabolites produced support the health of colon cells and contribute to maintaining the integrity of the intestinal lining.
A healthy microbiome also processes nutrients and converts them into more bioavailable forms that influence systemic health. The downstream effects of dysbiosis reduce beneficial metabolite production and/or increase production of harmful compounds that favor inflammation and oxidative stress (a state of excess free radicals, or unstable molecules, and lack of antioxidants to protect cellular structures).¹
Relationship to Metabolic Function
Microbial activity affects how calories are extracted from food and how certain metabolic pathways are regulated within the body, i.e., nutrient utilization and energy balance. Gut microbes contribute to the production of vitamins and metabolically active compounds that act upon signaling pathways involved in cell growth, differentiation, and apoptosis (cell death). Depending on the composition of the microbiome, metabolic outputs have been associated with both tumor-promoting and tumor-suppressing effects.¹
The gut-brain axis is also worth mentioning here. The microbiota influence neuroactive substances (e.g., serotonin, GABA) that affect brain chemistry, behavior, and mood, so maintaining a healthy gut can actually improve your emotional state.
Individual Microbiomes
The extent (or lack) of microbial biodiversity is unique to each individual and is shaped by a combination of environmental exposures, lifestyle, and biological factors. Our diets have an instrumental effect on the health and variety of intestinal microbes. In fact, eating patterns aligned with a Western diet (low fiber, high fat, high sugar, low nutrient) have been linked to changes in microbial diversity and function, which in turn are associated with increased colorectal cancer risk.¹
Antibiotics are among the greatest medical achievements of the 20th century, but they don’t just wipe out bacterial infections; they also clear out the good bacteria in the gut, allowing certain species to dominate. This disruption can create space for more resilient or potentially harmful species to become more prolific. Most of the time, the body can correct itself, but with prolonged antibiotic exposure, the composition of the gut undergoes more significant alterations that can have negative consequences for inflammation regulation, intestinal barrier function, and metabolite processing.
Researchers are also studying how early-life factors kickstart the intestinal environment, finding that mode of delivery (vaginal birth versus cesarean section) and duration of breastfeeding take part in establishing and developing microbial communities in the gut.²
The Connection to Colon Cancer
One of the functional consequences of dysbiosis is a decrease in beneficial microbial by-products, such as SCFAs, which protect the integrity of the gut barrier and support healthy communication between gut cells and the immune system. When SCFA levels drop, the intestinal lining can become less stable and more permeable than it should be.
At the same time, microbial imbalance can also increase the production of metabolites and signals that promote gut irritation. The combined effect of increased “bad bugs” and decreased “good bugs” results in a weakened intestinal barrier. The ability of inflammatory by-products to directly interact with immune cells in the gut wall triggers a sustained immune response, leading to chronic, low-grade inflammation in the colon.
A long-term inflammatory state is associated with increased oxidative stress and damage to nearby tissues, including the DNA within colon epithelial cells.
Disruptions to microbial diversity, stability, and functional output in the gut can create a biological environment characterized by increased inflammatory signaling and cellular stress. This type of environment, while not a direct cause of cancer, promotes downstream biological processes, such as abnormal cell growth and DNA damage, that are associated with cancer development.
Everyday Living
Even if not a simple one, the gut microbiome is a modifiable system.
Dietary patterns higher in fiber and plant diversity, while also low in ultra-processed foods and added sugars, contribute to microbial diversity and the production of beneficial metabolites. Limiting the overuse of antibiotics, or at least supplementing with pre- and probiotics after a round of these medicines, will keep the beneficial bacterial ecosystem healthy and flourishing. Consistent exercise, good sleep hygiene, and effective daily stress management, through effects on immune signaling and gut motility, also, surprisingly, interact with microbial stability.
Since excess adipose (fat) tissue is associated with chronic low-grade inflammation, hormonal dysregulation, and metabolic stress, weight management is also a contributing factor to maintaining a more resilient gut ecosystem. The environmental conditions of the gut in obese patients are typically more pro-inflammatory, and mechanisms to reduce excess body fat, including medical weight loss and bariatric surgery, introduce significant and rapid restructuring of this system. Procedures such as gastric bypass or sleeve gastrectomy alter nutrient flow, gastric acidity, and intestinal exposure to nutrients, and, as a result, many patients experience a more diverse and metabolically favorable profile over time. (The trajectory varies between individuals and surgical approaches.)
The combination of obesity-related alterations in the gut microbiome and a state of persistent inflammatory signaling reinforces a stronger pathway for cancer development. Following sustained weight reduction, improvements in metabolic regulation, reductions in systemic inflammation, and changes in gut microbial composition have all been observed. While this does not eliminate cancer risk, modifying biological factors that contribute to its development over time reduces it.
The board-certified surgeons at SAMPA specialize in weight loss and general surgeries, including procedures for correcting acid reflux and hernias. As pioneers of laparoscopic surgery in the Southeast, they performed the first laparoscopic cholecystectomy in Alabama and were the first in Mobile to perform laparoscopic colectomy, vagotomy, hiatal hernia, and adrenalectomy surgeries. They have performed over 8,000 weight loss surgeries since 1977 and focus on the science of weight loss.
References:
- Kim, J., & Lee, H. K. (2022). Potential Role of the Gut Microbiome In Colorectal Cancer Progression. Frontiers in immunology, 12, 807648. https://doi.org/10.3389/fimmu.2021.807648.
- Dharwadkar, P., Zaki, T. A., & Murphy, C. C. (2022). Colorectal Cancer in Younger Adults. Hematology/oncology clinics of North America, 36(3), 449–470. https://doi.org/10.1016/j.hoc.2022.02.005.
