Fiber and Colon Cancer: What’s the Connection?

Colon cancer is the third most common cancer in the U.S. But one simple dietary change can lower your risk of getting it: eating more fiber. 

If you are like most Americans, you are likely not eating nearly enough fiber. Read on to learn some easy ways to improve your fiber intake and lower your risk of colon cancer. 

What is fiber?

Dietary fiber is the part of plant food that you do not digest. There are two types of fiber: soluble and insoluble:

• Soluble fiber dissolves in water to form a gel. It helps absorb and eliminate cholesterol and sugars and is found in oats, psyllium, barley, and beans.

• Insoluble fiber does not dissolve but instead changes the consistency of the stool to help sweep out and clean the intestines. Insoluble fiber is found in whole grains, vegetables, and nuts. 

What do we know about fiber and colon cancer risk?

There are many health benefits of a high-fiber diet, including reducing the risk of colorectal cancer. 

A meta-analysis of 25 studies found that for every 10 g of fiber in your diet, your risk of colon cancer decreases by about 10%. 

We also know that increasing fiber after a colon cancer diagnosis may lower your risk of dying from colon cancer.

How does a high-fiber diet reduce your risk of colon cancer?

The way fiber reduces colon cancer risk is not entirely understood, but we know that fiber decreases tumor growth in animals. This may be because fiber: 

• Helps move stool through the gut more quickly. This can decrease the amount of time cancer-causing chemicals are in the intestines and help remove them from the body more quickly.

• Helps improve some of the common risk factors for cancer, including lowering blood sugar and helping you keep a healthy body weight. 

• Helps maintain a healthy gut microbiome (the trillions of microbes, such as bacteria and fungi, in your gut), which likely relates to cancer risk. While this is still an area of active research, we know the gut microbes make short-chain fatty acids, which can have anti-tumor effects.

How much fiber should I have daily to help prevent colon cancer?

The USDA recommends that you should consume between 25 g (for women) to 38 g (for men) of fiber daily. For lowering cancer risk, the American Institute for Cancer Research recommends getting at least 30 g of fiber per day. But what does this look like? Here’s what a day of eating roughly 30 g of fiber could look like:

Breakfast: 1 cup of oatmeal and an orange (7 g)  

Morning snack: 10 almonds (1.5 g)

Lunch: Sandwich using two slices of whole-grain bread (4 g)

Afternoon snack: Banana with 2 tbsp peanut butter (5.5 g)

Dinner: Your favorite protein served with half a cup of lentils and cooked spinach (9.5 g)

After-dinner snack: 2 cups popcorn (2.5 g)

Most Americans do not get enough fiber, with the average American getting only 16 g of fiber per day. 

What are some high-fiber foods?

Many foods have high amounts of fiber. Consider including more of the following in your diet:

• 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 and barley

• Corn, including popcorn

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

• Dark chocolate

What else can I do to adjust my diet to prevent colon cancer?

Beyond eating fiber, there are many steps you can take in your diet to help reduce your colon cancer risk, including:

• Avoiding red and processed meats

• Keeping a healthy weight

• Avoiding excessive alcohol 

• Focusing on a wide variety of plant-based foods

Why trust our experts?

Written by:

Christina Palmer, MD

Christina Palmer, MD, is a board-certified family physician with a focus on chronic care management, women’s health, and mental health. She’s the co-author of “Open Heart: When Open-Heart Surgery Becomes Your Best Option.”.

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:

Sophie Vergnaud, MD

Sophie Vergnaud, MD, is the Senior Medical Director for GoodRx Health. A pulmonologist and hospitalist, she practiced and taught clinical medicine at hospitals in London for a decade before entering a career in health education and technology.

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