The Benefits of Fiber: For Your Heart, Weight, and Energy

The Findings on Fiber and Colon Cancer

Since the early 70s, scientists proposed that a diet high in fiber could help prevent colon cancer. Colon cancer rates are significantly lower in cultures where people eat a large amount of high-fiber foods, so most of the research on fiber was directly related to colon cancer. 

In theory, fiber protects against colon cancers like this:

• Insoluble fiber from foods such as wheat bran adds bulk to stools and moves them through the GI tract swiftly, reducing the contact time with potential toxins in the colon.
• A bulky stool high in water can also dilute potential carcinogens.
• Fiber can also discourage growth of harmful bacteria and encourage healthy bacteria in the colon.

Studies on fiber have been inconclusive, however. Some show that higher fiber intakes are linked to a reduced colon and colorectal cancer, while others have not. The first setback for this theory came in 1999 from the Nurses’ Health study. Nurses who ate more dietary fiber did not have a lower incidence of colon cancer.  

The following year, a study indicated that eating a large amount of fiber each day (the recommended 25 to 38 grams) could reduce the risk of colon cancer by 40%. But in 2005, another observational study concluded that high dietary fiber intake was notassociated with a reduced risk of colorectal cancer.

Since then, more studies continue to show that colorectal cancer risk can be lowered with higher fiber intakes from fruit and vegetables.

Fiber Research: Breast and Prostate Cancers

Research has not turned up a strong link between fiber and prostate and breast cancers. The majority of studies have not found that eating dietary fiber significantly reduces breast cancer risk.

Few studies have examined the association between fiber and prostate cancer risk. But those that have showed that dietary fiber does not reduce prostate cancer risk.

Role of Dietary Fiber in a Cancer-Preventing Diet

Alice Bender, MS, RD, a nutritionist for the American Institute for Cancer Research, says the evidence on fiber and colon cancer, while mixed, is strong enough to make recommendations. “Our 2007 expert report looked at all the studies and concluded that foods high in fiber, not necessarily the fiber itself, can lower risk for colorectal cancer,” she tells WebMD.

“We know that a plant-based diet rich in fruits, nonstarchy vegetables, legumes, and whole grains is associated with a lower risk of a number of the most common cancers – colorectal, stomach, mouth, pharynx, larynx, and esophageal” Bender says.

Experts point out that there is not a single food, nutrient, fiber, or compound that provides the best cancer protection, however. It appears that the synergy of different foods working together is the most effective. 

“Eating a plant-based diet rich in phytochemicals, antioxidants, fiber, and other healthful plant compounds is the best way to prevent cancer -- along with regular physical activity, not smoking, and being at a healthy body weight” says Colleen Doyle, MS, RD, director of nutrition and physical activity for the American Cancer Society.

Bender and Doyle suggest these guidelines:

• Eat a mostly plant-based diet.
• Use the new American plate mode: Fill two-thirds of your plate with plants foods such as fruits, vegetables, whole grains, legumes, and nuts, and one-third with lean or low-fat animal products.
• Limit red meat to 18 ounces per week.
• Avoid processed meats.

An added plus: Plant-based foods are low in calories, which can help with weight control. Cancer experts say losing weight and getting your body mass index (BMI) into the healthy range may be more beneficial than fiber in reducing the risk of all cancers. Excess body fat is a contributor for a number of cancers, Bender says.

Make no mistake about it: Fiber is essential to your health. But if you want to reduce your risk of cancer, focus on the protective effects of whole foods such as fruits, vegetables, and grains. They contain a wealth of micronutrients and phytochemicals that work together to prevent disease.