Gut Health and Colon Cancer: What Your Diet Can Do

Your gut is home to trillions of bacteria, viruses, and fungi called the gut microbiota.

These microbes help digest food, make vitamins, and train your immune system.

Some gut bacteria produce compounds that protect the lining of your colon.

Other bacteria can produce compounds that damage colon cells over time.

Colorectal cancer starts in the colon or rectum, and it is one of the most common cancers worldwide.

Researchers now believe the balance of gut bacteria may be one piece of why some people develop colorectal cancer and others do not.

Scientists created a tool called the dietary index for gut microbiota, or DI-GM, to score how gut-friendly a diet is.

It gives points for foods linked to a healthy microbiome and subtracts points for foods linked to an unhealthy one.

• Fiber-rich foods like whole grains, beans, and vegetables
• Fermented foods like yogurt and kefir
• Foods high in prebiotics, such as onions, garlic, and asparagus
• Coffee and tea
• Foods rich in polyphenols, like berries and nuts

The index subtracts points for foods that tend to feed less helpful bacteria.

• Red meat and processed meat
• Refined grains
• Added sugar
• Saturated fat
• Alcohol

A higher DI-GM score means your everyday eating pattern likely supports a healthier mix of gut bacteria.

A large study used data from over 31,000 US adults in the National Health and Nutrition Examination Survey, collected between 2003 and 2023^[1].

Researchers compared DI-GM scores between people who reported a colorectal cancer diagnosis and those who did not.

People with colorectal cancer had noticeably lower DI-GM scores on average than people without it^[1].

After adjusting for age, lifestyle, and other health factors, higher DI-GM scores were linked to lower odds of colorectal cancer^[1].

People with the highest scores had about 30% lower odds of colorectal cancer than people with the lowest scores^[1].

This was a cross-sectional study, which means it looked at one point in time for each person.

It cannot prove that a gut-friendly diet prevents colorectal cancer, only that the two are linked.

Still, the finding fits with decades of other research connecting fiber, plant foods, and gut bacteria to colon health.

When you eat fiber, gut bacteria ferment it into short chain fatty acids like butyrate.

Butyrate is a key fuel source for the cells that line your colon.

It also appears to help control inflammation and support normal cell turnover in the colon.

A diet low in fiber and high in processed meat can shift the gut microbiome toward bacteria that produce harmful byproducts.

Some of these byproducts, like certain bile acids, can irritate or damage the cells lining the colon over time.

Chronic low grade inflammation in the gut is also thought to play a role in how normal cells can turn cancerous.

A more diverse, fiber-fed microbiome is generally linked to less of this inflammation.

Fiber's effect on gut bacteria may reach beyond cancer prevention into cancer treatment itself, since a scoping review found that higher dietary fiber intake was linked to a stronger immune response to immunotherapy in cancer patients^[2].

Researchers think this happens because fiber-fed gut bacteria produce short chain fatty acids that help activate immune cells that attack tumors^[2].

This suggests the same gut bacteria shaped by your everyday food choices may influence how well your body responds if cancer treatment is ever needed.

Vitamin D may also shape how well the gut lining repairs itself, since research on inflammatory bowel disease shows vitamin D helps regulate the immune cells and proteins involved in mucosal healing, the process of restoring the intestinal barrier after damage^[3].

You do not need a complicated plan to start supporting your gut microbiome.

• Eat beans, lentils, or chickpeas most days for fiber and plant protein
• Choose whole grains like oats, barley, and brown rice over refined grains
• Add a serving of yogurt, kefir, or another fermented food most days
• Eat a variety of vegetables and fruits each week, aiming for different colors
• Include prebiotic foods like garlic, onions, leeks, and asparagus
• Snack on nuts and seeds instead of packaged snack foods
• Limit red meat and processed meat like bacon, sausage, and deli meat
• Cut back on added sugar and heavily refined foods
• Drink coffee or tea if you already enjoy them, since both are linked to a favorable gut microbiome

Aim for variety rather than perfection, since different plant fibers feed different helpful bacteria.

A simple goal is 25 to 35 g of fiber a day, spread across meals rather than all at once.

Changing your fiber intake slowly can help avoid bloating or gas as your gut adjusts.

This information is useful for almost everyone, since colorectal cancer is common and diet is something you can control.

• Adults over age 45, since colorectal cancer risk rises with age
• People with a family history of colorectal cancer or polyps
• People who eat a lot of red or processed meat regularly
• People with a diet low in fiber and plant foods
• Anyone with digestive symptoms they have not discussed with a doctor

Diet changes work alongside, not instead of, recommended colorectal cancer screening.

Screening guidelines and personal risk should always be discussed with a healthcare provider.

Put this to work in your own food log. Track it free with Ration →