Does a High-Fiber Diet Help to Prevent Cancer? We Examine the Connection

If you are like most Americans, you are not getting enough fiber in your diet. This may mean you are missing out on some of the many health benefits that fiber provides, like improved blood sugar and cholesterol, help with maintaining a healthy weight, and even lowering cancer risk. Increasing fiber in your diet can be as easy as making some simple changes. 

Read on to learn more about the connection between a high-fiber diet and cancer prevention. 

What is fiber?

Dietary fiber is a part of plant food that you cannot digest. There are two types of fiber: soluble and insoluble. Most plants contain both soluble and insoluble fiber but will have different amounts of each.

• Soluble fiber is partially digested and can help lower cholesterol by absorbing and eliminating it. Soluble fiber is found in oats, psyllium, grains, and vegetables. 

• Insoluble fiber cannot be digested. It changes the consistency of our stool, which then helps to sweep out and clean the intestines. Most fruits, beans, and nuts have insoluble fiber.

How do fiber-rich foods help to reduce the risk of cancer?  

A high-fiber diet has many health benefits, and studies have shown it reduces the risk of some cancers. While we don’t know exactly how fiber may reduce cancer risk, it likely has to do with the fact that it helps improve some of the common risk factors for cancer. These include:

• Lowering blood sugar and helping you keep a healthy body weight, which can decrease the risk of many cancers.

• Changing estrogen production, which may lower breast cancer risk because estrogen can stimulate the growth of breast cancers.

• Helping eliminate cancer-causing chemicals from the intestines, which may lower colon cancer risk.

• Maintaining a healthy gut microbiome (the trillions of microbes, such as bacteria and fungi, in your gut), which likely has a relationship with cancer risk though this is still an area of active research.

What types of cancer may be reduced by diets rich in fiber? 

There is some evidence suggesting that high-fiber diets reduce the risk for specific types of cancer, including: 

• Colorectal cancer

• Gastric cancer

• Breast cancer (particularly if fiber is consumed between the ages of 10 and 19)

What are some examples of high-fiber foods?

Many foods contain high amounts of fiber. Some examples include:

• Fruits, especially raspberries, mangoes apples, and strawberries

• Vegetables, especially carrots, broccoli, collard greens, and artichokes

• Lentils

• Beans including black beans, kidney beans, and chickpeas

• Oats

• Whole grains, including quinoa, whole grains, and barley

• Corn, including popcorn

• Nuts and seeds including almonds, chia seeds, and flax seeds

• Dark chocolate

You can also increase fiber by taking a fiber supplement or eating foods with added fiber. But remember, the best source of fiber is from whole foods because you also get many other nutritional benefits, including vitamins, minerals, and antioxidants.  

Everyday tips for adding high-fiber foods to your diet

The USDA recommends that you should consume between 25 g to 38 g of fiber daily, depending on your age and gender. As many as 95% of Americans do not get enough fiber. In fact, the average American gets only 16 g of fiber per day.

Increasing fiber in your diet can be as simple as making small swaps. Consider the following:

• Replace juice with eating the actual fruit

• Choose whole grains (brown rice, whole wheat, buckwheat, oatmeal) over refined grains (where much fiber has been removed, such as white rice, processed bread, and cereals).

• Snack on nuts, fruits, vegetables, or popcorn

• Consider beans instead of meat as a source of protein

• Start your meal by filling up with vegetables

• Sprinkle chia seeds or flax seeds on your meals

• Eat the peels of your fruits and vegetables (be sure to clean them first!)

Remember, start increasing your fiber intake slowly and make sure you also increase your water intake. Too much fiber too fast could cause some initial abdominal pain or bloating, but over time your intestines will adapt to the higher fiber intake.

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Written by:

Christina Palmer, MD

Christina Palmer, MD, is a board-certified family physician with a special interest in chronic care management, women’s health, mental health, and preventive care. She has over 10 years of experience in primary care research, innovation, and practice.

Edited by:

Kelsey Abkin

Kelsey Abkin has been working as a journalist since 2016. She has held many titles throughout her career, including editor, content strategist, digital strategist, and writer.

Reviewed by:

Katie E. Golden, MD

Katie E. Golden, MD, is a board-certified emergency medicine physician and a medical editor at GoodRx.

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