More than 107,000 people are expected to be diagnosed with colon cancer this year, along with an additional 46,000 cases of rectal cancer, according to the American Cancer Society. Some risk factors for colorectal cancer are beyond your control, like inherited gene mutations, a history of inflammatory bowel disease, or having undergone radiation in the abdominal area. Yet, more than half of all colorectal cancer cases are linked to lifestyle-related factors that can be changed. Drinking moderate to heavy amounts of alcohol, smoking, having type 2 diabetes, or being overweight all increase your risk.
Diet also plays a key role. Eating a lot of red or processed meat — especially when it’s cooked at high temperatures — has been shown to raise colon cancer risk. And if you follow a low-carb eating plan, it’s worth paying attention to your fiber intake. A 2025 study in Nature Microbiology found that a low-carb diet lacking in fiber can trigger inflammation in the gut. That inflammation weakens the gut’s natural defenses, making it easier for harmful bacteria to promote the growth of colon polyps.
How fiber may reduce colon cancer risk
Specifically, the study compared how different diets affected the gut microbiome in lab mice. Some mice were fed a normal diet, while others ate a high-fat, high-sugar diet or a low-carb, low-fiber diet. All of the mice were then exposed to a strain of E. coli known to produce a toxin linked to colon cancer. The mice on the low-fiber diet ended up with a weakened gut lining and higher nitrate levels, which gave the harmful E. coli a better chance to grow. But when the mice were given extra fiber, the inflammation in their guts went down.
Your gut is home to more than 1,000 types of bacteria — some helpful, some not so much. According to a 2014 article in the World Journal of Gastrointestinal Oncology, fiber feeds the good bacteria and reduces the harmful bacteria. As your gut bacteria break down fiber, they produce short-chain fatty acids (SCFAs). One SCFA called butyrate promotes healthy colon cells and slows the growth of colon cancer cells. Another SCFA, called acetate, helps protect your colon cells from DNA damage.
Fiber also adds bulk to your stool, which helps move waste through your system and reduces the amount of time harmful substances stay in contact with your colon lining. It also helps sweep out potentially cancer-causing compounds and lowers your colon’s pH, creating an environment where bad bacteria struggle to survive.
Add fiber to your low-carb diet
Some low-carb diets are healthier than others. Simply cutting out carbs can have you missing out on the 25 to 30 grams of fiber recommended every day. The carnivore diet eliminates all plant-based foods, which are your main sources of fiber. The keto diet will limit your carbs to maybe 50 grams or less per day. You can still enjoy the benefits of a low-carb diet while keeping your gut healthy by making those carbs rich in fiber.
Legumes such as lentils or black beans can be your best bet for fiber, but they may not suit diets that are extremely low in carbs. However, legumes are high in soluble and insoluble fiber to improve your gut microbiome. Some of your best high-fiber foods that are low in carbs are cruciferous vegetables, nuts, and seeds. A cup of cooked artichokes offers almost 8 grams of fiber, and an ounce of chia seeds packs almost 10 grams of fiber. By including a cup of avocado in your low-carb menus, you’ll be adding another 10 grams of fiber to help reduce your colon cancer risk.
