Confused About Fiber?

The American Institute for Cancer Research

In a March 30, 2001, press release, the American Institute for Cancer Research reviews the confusing evidence about fiber and cancer, as well as fiber and other health issues.

WASHINGTON -- The American Institute for Cancer Research has issued a new brochure, "The Facts about Fiber," to clarify confusion raised by reports of recent studies, and help people identify sources of dietary fiber to ensure they get enough in their daily diet. (See Editor's Note at end for information on how consumers can receive this free brochure.)

For many years, scientists have studied dietary habits in several countries where more fiber and less fat is consumed than in the United States. People in those countries have a lower incidence of heart disease and certain cancers, such as colorectal cancer, than Americans do.

Because it bulks up the stool and speeds elimination of body wastes, scientists have long explored the link between fiber and a lower risk for colon cancer. As early as 1811, British physician J. Howard proposed that constipation was an important factor in cancer risk, in his book Practical Observations on Cancer.

Scientists often extracted fiber from food and fed it to people as a supplement. A study published in the New England Journal of Medicine in April 2000 caused quite a stir by reporting no significant effect in the recurrence of colon polyps after a three-year supplementation.

In fact, an international panel of 16 scientists, acting on behalf of AICR, reviewed all the existing research on fiber and colon cancer in 1997. They found only weak evidence for a link between fiber supplementation and reduced risk of colon cancer.

"But that does not mean that foods rich in fiber also fail to reduce cancer risk," says Dr. Ritva Butrum, AICR's Vice President for Research. "In fact, the majority of research studies suggests that fiber-rich foods, as opposed to fiber supplements, are effective in reducing risk of colorectal cancer."

The same panel of international experts also reviewed 26 studies on the link between vegetables, which are fiber-rich, and colorectal cancer. Twenty-one studies showed a positive relationship.

After carefully weighing all the evidence, these scientists concluded, "Evidence that diets rich in vegetables protect against cancer of the colon and rectum is convincing."

This conclusion, according to Butrum, is not surprising. "In addition to dietary fiber, vegetables offer vitamins, minerals and phytochemicals -- naturally occurring 'plant chemicals' that work together to lower cancer risk," she says. "The anti-cancer power of fiber working with those substances is much greater than any one of them working alone."

Reports of a second study, which also appeared in NEJM's April 2000 issue, confused this issue further. After counseling study subjects to follow diets high in fruits and vegetables for four years, research reported no decrease in the polyps that can grow into tumors.

But those same researchers pointed out that a cancer can take decades to develop, and a longer intervention might have produced more positive results.

Furthermore, studies of the carotenoid level in the blood of the subjects suggested that many may not have actually followed the diet assigned. Blood carotenoids are considered an effective indicator of fruit and vegetable consumption.

"No research study is perfect," comments Butrum. "That is why people should draw conclusions about healthy eating from the preponderance of evidence, not single studies. In this case, the great majority of studies indicates that fiber-rich vegetables help reduce risk of colorectal cancer."

Fiber -- Why Do We Need It?
Dietary fiber involves many important functions that help protect our health:

• It helps maintain a steady level in blood sugar and insulin;
• Fiber keeps appetites satisfied longer;
• It stimulates the production of substances that regulate growth of cells lining the colon -- a safety guard against cancer's out-of-control pattern of growth;
• Fiber protects the lining of the colon by collecting and holding damaging bile acids; and
• Fiber dilutes harmful substances, speeds their elimination -- and prevents constipation in the process.

In addition to reducing cancer risk, fiber has been shown to help reduce the risk of heart disease. For example, in countries where the typical diet is high in fiber and low in fat compared to the average U.S. diet, people have a lower incidence of heart disease than Americans. Whole grains, an important source of dietary fiber, may also reduce the risk of stroke.

Fiber can also significantly reduce the risk of diabetes and obesity. Getting enough fiber also helps alleviate conditions related to colon function, including hemorrhoids and diverticulosis.

Fiber in Foods -- The Best Sources
Animal products like meat, cheese and eggs contain no fiber. Only plant foods -- fruits, vegetables, whole grains, beans, nuts and seeds -- can provide the fiber essential to good health.

Some vegetables, fruits and grain products are higher in fiber than others. For example, a half-cup of cooked carrots has four times as much fiber as a cup of raw spinach. A medium baked potato contains more fiber than one-half cup of cooked brown rice. Whole wheat bread has twice as much fiber as white bread.

No matter what the specific foods selected, however, eating a variety of fruits, vegetables, grains and beans can easily ensure the daily recommended intake of fiber. Five daily servings of fruits and vegetables, plus seven servings of whole grains and beans, will not only provide essential fiber, but also the nutrients and phytochemicals that are also critical to lowering cancer risk.

Getting Fiber In The Diet -- How Much, How Easy?
Nutrition experts suggest eating between 20 and 35 grams of fiber each day. Although this may seem to represent a great deal of food to average consumers, it's not as difficult as they might think.

According to Melanie Polk, R.D., AICR's Director of Nutrition Education, "A day's worth of meals can easily attain the ideal goal of 20 to 35 grams of fiber." She describes how 30 grams of fiber could easily be included in an ordinary day's three meals:

• A breakfast that includes a cup of raisin bran cereal (7 grams) and a banana (3 grams);
• A lunch sandwich of two slices of whole wheat bread (4 grams), filled with a quarter-cup of hummus (4 grams), followed by an orange (3 grams) for dessert; and
• Dinner, including a small baked potato with skin (3 grams), a half-cup of mixed vegetables (4 grams) and a cup of strawberries (4 grams).

Polk observes, "The fiber in these three meals totals 32 grams, which is within the recommended range."

Editor's Note: Consumers can receive a free copy of AICR's brochure, "The Facts About Fiber," by calling (800) 843-8114, extension 35, between 9 a.m. and 5 p.m. EST, Monday through Friday.

The American Institute for Cancer Research (AICR) is the nation's third largest cancer charity, focusing exclusively on the link between diet and cancer. The Institute provides a wide range of consumer education programs that help millions of Americans learn to make dietary changes for lower cancer risk. AICR also supports innovative research in cancer prevention and treatment at universities, hospitals and research centers across the U.S. The Institute has provided over $57 million in funding for research in diet, nutrition and cancer. AICR's Web address is www.aicr.org .