The Facts about Fiber

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Fiber is a type of carbohydrate and should be one of your favorite parts of a cancer-protective diet. There are two types, soluble fiber, and insoluble fiber, and both have different effects on the body.

Soluble Fiber

This acts like a sponge inside the body. The “soluble” in soluble fiber indicates that this type of fiber dissolves in water and swells up to form a gel-like substance. The gel-like substance takes up more space in your system and creates a feeling of fullness.

Due to its ability to absorb water, it helps bulk up stools and slows down the time it takes for you to excrete waste. Increasing this type of fiber in your diet can help to reduce diarrhea or help to bulk up loose stools. Soluble fiber also slows the absorption of glucose (sugar) into our bodies, minimizing the spike in blood sugar in our bodies after a meal, helping to better regulate our blood sugar levels overall.

Sources of Soluble Fiber

Many foods contain a mixture of soluble and insoluble fiber; however, some foods contain very high levels of one particular type. Soluble fiber is found in apples, carrots, oats, apricots, oranges, bananas, eggplant, flaxseeds, and legumes such as peas, beans, and lentils.

Insoluble Fiber

This kind of fiber is the one that most people think of as ‘roughage’. As opposed to soluble fiber that dissolves into water, insoluble, as its name implies, does not dissolve in water and passes through untouched, sweeping the colon clean and helping to keep the bowel opening regularly. Another benefit of insoluble fiber is its ability to become fermented in the colon thus providing a food source for good bacteria that live in our colon. Insoluble fiber increases the frequency of stools and can help to alleviate constipation or sluggish bowels.

Sources of Insoluble Fiber

Insoluble fiber is found in nuts, seeds, whole grain products, and brassica vegetables such as broccoli, cauliflower, kale, arugula, and many skins of fruits (another reason to eat the skins!).

The American dietary guidelines recommend consuming between 22-32g of fiber per day depending on the age and sex of the individual. The current average intake for an American adult is around 16g per day.

The American Institute of Cancer Research recommends 30g per day to enjoy the full health benefits of fiber. To achieve this, you need to eat at least 5 portions of fruit and vegetables per day and also consume some whole grains, such as oats, brown rice, quinoa or farro or whole wheat bread or pasta, and legumes such as black, kidney, garbanzo, and lentils.

Fiber isn’t just important for cancer prevention. Soluble fiber binds to bile acids in the intestine preventing the reabsorption of bile back into our bodies. Thus, the bile acids become “trapped” in the gel-like substance created from the soluble fiber that passes right out of your body through your stools. Bile acids made from cholesterol, preventing them from being reabsorbed means that blood cholesterol levels may fall, which can be helpful for heart health and preventing other forms of chronic disease.


If your diet consists mostly of highly processed refined foods, it’s a smart idea to make the change to include more fiber-rich foods, but it’s not a good idea to suddenly start eating 30g of fiber per day. The body needs time to adjust to higher fiber levels and doing too much too fast can lead to bloating, gas, and constipation – effects that might make you think eating more fiber won’t agree with you.

Easy ways to initially increase your fiber intake: switch to wholegrain cereals, bread, and pasta, plus leave the skin on fruits and vegetables like apples and potatoes, as this is where the majority of the fiber is contained. Allow your body to get used to these changes before increasing fiber further.

Check out our high fiber recipes for some inspiration on ways to get more of that fabulous fiber into your diet.

Kate Ueland, MS, RD specializes in oncology nutrition, primarily working with breast, ovarian, renal, and melanoma cancer patients throughout all stages of the cancer journey at Seattle Cancer Care Alliance (SCCA) in Seattle, WA. As Cook for Your Life’s nutrition advisor and editor, Kate ensures all culinary content adheres to the Academy of Nutrition and Dietetics and follows science-based guidelines.

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Reviews & Comments

Nelson Lowe
Rated 0 out of 5
July 22, 2020

I'm in the need to change for more Fiber.

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