The #1 Nutrient to Help Lower Risk of Colorectal Cancer

Colorectal cancer, frequently referred to as colon or rectum cancer, is the fourth most common cancer and the second leading cause of cancer-related deaths in the United States. Approximately 4% of adults will be diagnosed with colorectal cancer in their lifetime, with an estimated 154,270 individuals likely to be diagnosed in 2025 alone, according to the Colorectal Cancer Alliance. 

Some risk factors for colorectal cancer can’t be changed, like your age, sex, genetics and personal or family history of colorectal polyps or colorectal cancer. However, your diet is a key risk factor that you do have control over. In fact, registered dietitian Karen Collins, M.S., RDN, CDN, FAND, nutrition advisor to the American Institute for Cancer Research, says, “Colorectal cancer is considered one of the cancers most influenced by diet and lifestyle. Our daily choices make a difference!” While your overall eating pattern makes the biggest difference when it comes to colorectal cancer risk, fiber is the most important nutrient for minimizing your risk.

“Fiber is truly a powerhouse when it comes to helping to protect your colon,” says board-certified oncology dietitian Alison Tierney, M.S., RD, CSO, founder of Wholesome LLC. In this article, dietitians explain why fiber is the No. 1 nutrient to help reduce your risk of colorectal cancer and share other strategies for prevention.  

Why Fiber Can Help Lower the Risk of Colorectal Cancer 

It Keeps Things Moving 

Research shows that both soluble and insoluble fiber may help reduce the risk of colorectal cancer by keeping food moving through your digestive tract. Soluble fiber softens stools, making them easier to pass, while insoluble fiber adds bulk to your stool and draws water into your colon to keep things moving. Besides making your bathroom visits more pleasant, staying regular may also help prevent colorectal cancer by reducing the amount of time colon cells are exposed to potential cancer-promoting compounds that may be in your stool. 

Tierney puts it more simply: “This means less time for harmful substances to hang around and potentially damage the cells lining your colon.” For optimal benefits, aim to eat a variety of fiber-rich foods, like whole grains, legumes, nuts, seeds, fruits and vegetables, throughout the day.

It Produces Compounds with Potential Anticancer Effects 

Unlike many nutrients, fiber isn’t digestible. Instead, it gets fermented by bacteria in the gut, producing short-chain fatty acids, like butyrate, which offer some pretty impressive health benefits. Emerging research suggests that these short-chain fatty acids may help protect against (and possibly slow down the progression of) colorectal cancer. “Short-chain fatty acids [may] protect colorectal cells from damage [by] reducing markers of inflammation and showing effects on gene expression that could reduce cancer development,” says Collins.

Short-chain fatty acids may also help reduce overweight and obesity—additional risk factors for colorectal cancer., 

It May Reduce Insulin Resistance 

According to one study, people with type 2 diabetes have a 47% increased risk of colorectal cancer. While the exact mechanism is unclear, it’s thought that this higher risk is due to higher levels of insulin in people with diabetes. There are many contributing factors to diabetes. However, a high-fiber diet may be protective by improving insulin resistance—a condition that, over time, can lead to type 2 diabetes. 

It May Increase Your Intake of Antioxidants

“Eating more fiber usually means you’re eating more whole plant foods—like fruits, veggies, beans and whole grains—which also come packed with antioxidants and cancer-fighting nutrients,” says Tierney. Research suggests that antioxidants in fiber components may be especially beneficial for colon health., Because they aren’t digested, these antioxidants make their way into the colon where they can help reduce inflammation and support intestinal health.

Other Strategies to Lower Your Risk

Eating more fiber is just one piece of the puzzle when it comes to lowering your risk of colorectal cancer. “Rates of early-onset colorectal cancer (occurring in people under age 50) are rising, and risk is considered to be reduced by these same lifestyle factors as colorectal cancer that occurs in older adults,” says Collins. 

Here are a few strategies for reducing your risk: 

• Cut Back on Processed and Red Meats: Eating red or processed meats, including bacon, deli meats and sausage, is linked with an increased risk of colorectal cancer. The American Institute for Cancer Research recommends consuming no more than 12 to 18 ounces of unprocessed red meat (like beef, pork and lamb) per week and avoiding processed meats as much as possible.
• Limit Alcohol Consumption: Collins explains that alcohol is converted in the body to acetaldehyde, a cancer-promoting compound that damages DNA and makes repairing this damage harder. If you choose to drink, Collins recommends doing so in moderation, meaning no more than one standard drink per day for women and no more than two for men. Better yet, swap the alcohol for a glass of milk! Thanks to its calcium content and naturally present short-chain fatty acids, cow’s milk may help protect against colorectal cancer. 
• Get Moving: Regular physical activity has numerous benefits for health, including helping to improve insulin sensitivity, reducing chronic inflammation and supporting digestive health—all of which play a role in colorectal cancer risk. Aim for at least 150 minutes of moderate activity per week. 
• Eat More Plants. While you don’t need to eat plant-based 100% of the time, Tierney says that eating more minimally processed, plant-based foods is one of the best ways to reduce your risk of colorectal cancer. “Whole plant foods give you not just fiber, but also a wide range of nutrients that help reduce inflammation and support a healthy gut and immune system,” she says. 

The Bottom Line

The dietitians we spoke with unanimously agree that fiber is the No. 1 nutrient to eat more of to lower your risk of colorectal cancer. Fermentation of fiber in the gut leads to the production of short-chain fatty acids, which may have anticancer effects and support weight management. Fiber is also beneficial thanks to its positive effects on gut health, insulin resistance and chronic inflammation. 

When it comes to cancer prevention, there’s no one magic nutrient or habit. Instead, your overall lifestyle will have the biggest impact. Staying physically active, limiting alcohol intake, prioritizing plant-based foods and eating less red meat and processed meats are key strategies for prevention.