This year, over 107,000 people are anticipated to receive a colon cancer diagnosis, in addition to 46,000 new cases of rectal cancer, as projected by the American Cancer Society. While some factors contributing to colorectal cancer risk are uncontrollable, such as inherited genetic mutations, a history of inflammatory bowel disease, or prior abdominal radiation, more than half of the cases are linked to modifiable lifestyle factors. These include moderate to heavy alcohol consumption, smoking, type 2 diabetes, and obesity.
Diet is also a significant factor. Consuming large amounts of red or processed meats, particularly when cooked at high temperatures, has been associated with an increased risk of colon cancer. Additionally, individuals on low-carb diets should be mindful of their fiber consumption. A 2025 study published in Nature Microbiology indicated that a low-carb, low-fiber diet might trigger gut inflammation. This inflammation can compromise the gut’s defenses, facilitating the growth of colon polyps by harmful bacteria.
How fiber may reduce colon cancer risk
The study specifically examined the effects of different diets on the gut microbiome in lab mice. Some mice consumed a standard diet, while others were given a high-fat, high-sugar diet, or a low-carb, low-fiber diet. All mice were subsequently exposed to a strain of E. coli known for producing a toxin associated with colon cancer. Those on the low-fiber diet exhibited a weakened gut lining and elevated nitrate levels, creating an environment conducive for the harmful E. coli to thrive. However, providing extra fiber reduced gut inflammation in these mice.
The human gut hosts over 1,000 bacterial species, some beneficial and others less so. According to a 2014 article in the World Journal of Gastrointestinal Oncology, fiber nourishes beneficial bacteria and curtails harmful ones. As gut bacteria digest fiber, they produce short-chain fatty acids (SCFAs). One SCFA, butyrate, supports healthy colon cells and inhibits cancer cell growth, while acetate, another SCFA, protects colon cells from DNA damage.
Fiber also adds bulk to stools, facilitating waste movement through the digestive system and minimizing the contact time of harmful substances with the colon lining. It sweeps away potentially carcinogenic compounds and lowers colon pH, an environment unfavorable for harmful bacteria.
Add fiber to your low-carb diet
Not all low-carb diets are equally healthy. Simply reducing carbs might lead to missing out on the recommended 25 to 30 grams of daily fiber. Diets like the carnivore approach exclude all plant-based foods, the primary fiber sources. The keto diet restricts carbs to about 50 grams or fewer daily. However, you can maintain a low-carb diet while supporting gut health by ensuring your carb intake is fiber-rich.
Legumes, such as lentils and black beans, are excellent fiber sources, though they may not fit extremely low-carb diets. These legumes provide both soluble and insoluble fiber, enhancing gut microbiota. Other high-fiber, low-carb options include cruciferous vegetables, nuts, and seeds. A cup of cooked artichokes offers nearly 8 grams of fiber, while an ounce of chia seeds contains almost 10 grams. Including a cup of avocado in your low-carb meals can add another 10 grams of fiber, helping to lower the risk of colon cancer.
