Can Fiber Decrease My Risk of Colon Cancer?

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The scientific studies are inconclusive - they cannot prove fiber decreases the risk of colon cancer, yet they also cannot prove it doesn't. How do you know if you should be counting your grams of fiber or not?

Decades of studies have provided conflicting answers to this question. The bottom line: Fiber is good for you, regardless of whether or not it decreases your risk of colon cancer.

Close-Up of Muesli With Fruits In Bowl
Wanwisa Hernandez / EyeEm / Getty Images

Even if someday science definitively concludes that dietary fiber does not impact your colon cancer risk, it will help reduce your risk of high cholesterol, obesity, type 2 diabetes, heart disease, and certain digestive disorders.


Tips For Preventing Colon Cancer

Types of Fiber

Studies that support high-fiber diets to reduce your risk of colon cancer all have one thing in common – it's not just the amount of fiber you eat, but the type. Sure, you can pick up a box of refined cereal that has the fiber and nutrients put back into it (i.e., fortified) or even pop a few fiber pills, but some studies say that they won’t make your colon as happy as eating the real deal from nature.

More food for thought: If you get all of your dietary fiber out of a supplement, you are missing out on the natural benefits of fibrous foods. Fruits and vegetables are rich in antioxidants, micronutrients, and phytochemicals – all of which are proven to promote health.

What Is Fiber?

Natural dietary fiber is the indigestible portion of plant food. Roughage, bulk, "fibre" (if you live on the European side of the pond) are terms for the same concept—dietary fiber.

Soluble vs. Insoluble

Dietary fiber is classified as either soluble or insoluble. Try not to get wrapped up in what kind of fiber you eat, just focus on getting a nice mix of both types. Eating a healthy diet rich in fruits, vegetables, lentils, and whole grains will provide a healthy mix.

Soluble fiber is partially digestible and turns gelatinous in your colon. It slows digestion and can help decrease cholesterol.

  • Grains
  • Most vegetables

Insoluble fiber is non-digestible and passes through your colon virtually unchanged. It speeds up digestion and "bulks" up your stools but does not impact cholesterol.

Examples of insoluble fiber include:

  • Most fruits
  • Beans, lentils
  • Seeds and nuts


The three forms of any grains are whole, refined and fortified (enhanced). In their unchanged, natural state, all grain fibers have three basic layers:

  • Endosperm – the innermost layer. Contains very little fiber.
  • Germ - the middle layer. Contains moderate fiber.
  • Bran - the outer layer. Contains the highest fiber and micronutrient content.

Whole grains contain all three layers, which means they have the highest fiber and nutrient content. They are virtually unchanged from harvest to your table. Refined grains have been stripped of their bran and germ layer, leaving the flavorful and less fibrous endosperm only. Fortified grains have been stripped of their natural layers, and man-made fiber and nutrients are bonded back onto the grain.

Science says that at least half of our daily grains should be whole grains. Whole grains include:

  • Whole wheat
  • Whole oats
  • Brown or wild rice
  • Millet
  • Popcorn
  • Quinoa
  • Buckwheat

Refined grains are found in cereals, processed foods, white rice, and white breads. They provide very little in the way of dietary fiber and are sometimes full of calories.

Aside from grains, you can get much of your daily fiber from beans, fruits, and vegetables. One apple, banana, orange or carrot contains about 2 to 3 grams of fiber. Potatoes (skin on), corn and broccoli have a little more fiber, at about 4 to 5 grams, depending on your serving size. Cooked beans and figs are full of fiber; ½ cup cooked beans or just three figs (dried) provide 8 or more grams of fiber.

Benefits: The Broom to Your Colon

Fiber plays a couple of vital roles as it travels through your digestive tract:

  • Increases peristalsis – the movement of stool through your colon
  • Helps regulate bowel movements
  • "Sweeps" toxins out of your colon
  • Absorbs irritants, such as bile acids from digestion
  • Makes you feel "full" longer and may help with weight control
  • Binds with cholesterol and reduces bad cholesterol in the blood

How Much Do I Need?

On average, the recommended daily allowance (RDA) for fiber varies between men and women and is dependent on the person's age. Men 50 years and younger should aim for at least 38 grams of fiber each day. Women 50 years and younger need about 25 grams of fiber per day. Men and women over 50 years require slightly less fiber - 30 grams daily for men and 21 grams daily for women.

Getting Enough Fiber If You Avoid Gluten

If you have celiac disease or any form of gluten intolerance, never fear. You can still increase the fiber in your diet; however, you will have to avoid some of the gluten-rich grains, such as barley, wheat, and rye. There are many fibrous foods that are gluten-free, including:

  • Fruits
  • Vegetables
  • Chickpeas
  • Flaxmeal
  • Amaranth flour

When in doubt, talk to your healthcare provider about increasing the fiber in your diet. A word of warning: don’t increase your fiber intake too rapidly or bloating, gas, and cramps can follow. Along with adding fiber slowly, you will want to increase your water intake. Although hydration requirements vary from person to person, the average person requires eight, 8-ounce glasses of water daily.

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

By Julie Wilkinson, BSN, RN
Julie Wilkinson is a registered nurse and book author who has worked in both palliative care and critical care.