Fiber and colorectal cancer: Lower risk and prevention

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According to American Cancer Society (ACS) estimates, there were 106,970 new cases of colon cancer in the United States and 46,050 new cases of rectal cancer in 2023. Colorectal cancer is the third most common cancer doctors diagnose in adults in the United States, excluding skin cancers.

A diet full of fruits, vegetables, and whole grains, with limited red and processed meat and sugary drinks, likely lowers a person’s risk of colorectal cancer.

Cancer Research UK notes that a high fiber diet may reduce a person’s risk of bowel cancer because:

• Fiber increases stool frequency and bulk and dilutes the contents of stool. Therefore, harmful chemicals leave the bowel sooner.
• Bacteria in the bowel that come into contact with fiber make butyrate, which helps maintain cell health in the bowel and reduces the chances of tumor growth.

A 2019 meta-analysis of data from 49,964 people in Asia also concluded that dietary fiber was protective against colorectal cancer. However, the researchers noted possible analysis limitations, such as publication bias, since the full text of some potentially eligible studies was not accessible.

According to the American Institute for Cancer Research (AICR), people should aim to eat a minimum of 30 grams (g) of fiber a day.

This translates to an average increase of 12–15 g daily for adults in the United States to meet the AICR’s 30g daily recommendation.

AICR data suggests that every 10 g increase in fiber relates to a 7% reduced risk of colorectal cancer.

A study from 2020 recommends that doctors advise people to eat whole grains as a source of fiber to help prevent colorectal cancer.

The study revealed an association between eating whole grains and a lower chance of developing colorectal cancer, especially rectal cancer.

Additionally, a 2017 data assessment from two prospective cohort studies found that people who started eating more fiber after a colorectal cancer diagnosis had a lower chance of dying. Each 5 g a day fiber increase correlated with an 18% lower chance of dying from colorectal cancer.

Specifically, the researchers found an association between cereal fiber intake and the risk of dying from colorectal cancer. They also found an association between vegetable fiber intake and the overall risk of dying but not specifically due to colorectal cancer.

A 2020 study in the journal Nutrientsreported a link between eating dietary fiber and:

• overall metabolic health
• cardiovascular disease
• colon health
• gut motility, which is the movement of food through the gastrointestinal system, from the mouth to the anus
• risk of colorectal cancer
• chances of dying

Additionally, the gut microflora uses dietary fiber to help with appetite regulation, metabolism, and regulating the inflammatory response.

The Centers for Disease Control and Prevention (CDC) suggests several ways to increase fiber in the diet:

• Add fiber to breakfast, such as having avocado toast topped with chickpeas or a bowl of oatmeal with nuts and berries.
• Choose whole grains, such as bread that lists whole grain flour as the first ingredient, brown rice, quinoa, or whole wheat pasta.
• Eat more nonstarchy vegetables, such as leafy greens, spinach, broccoli, or frozen mixed vegetables.
• Eat legumes, such as lentils, peas, or different kinds of beans (pinto, kidney, lima, navy, garbanzo).
• Snack on fruit, vegetables, nuts, and seeds, such as apples, pears, bananas, baby carrots, almonds, sunflower seeds, and pistachios.

Colorectal cancer refers to cancer that starts in the colon or the rectum.

A fiber-rich diet may reduce a person’s chances of developing colorectal cancer. Increasing intake after diagnosis may also reduce a person’s chances of dying from the disease.

Fiber intake can also help maintain digestive, cardiovascular, and metabolic health.

People can increase their fiber intake by choosing whole grains, nonstarchy vegetables like spinach and broccoli, and beans and pulses.