Does More Fiber Equal Less Cancer?

Should you "give a fig" about fiber?

Maybe. Fiber might play a role in protecting you from colon cancer, according to two major studies.

People who ate the most fiber had a drastic reduction in their risk of colon cancer. Diets averaging 35 grams of fiber a day translated into the risk for colon cancer dropping by 40 percent, compared to people eating only 15 grams, according to the largest scientific study to investigate the links between diet and cancer risk.

The European Prospective Investigation into Cancer (EPIC) report, published in the British medical journal The Lancet, tracked the diets of a half million people in 10 European countries for an average of four-and-a-half years.

Complementing that study is a separate report from the United States appearing in the same journal issue. People who ate more than 30 grams a day had their risk of polyps reduced by 20 percent compared to those who ate less than 15 grams.

Scientists with the Prostate, Lung, Colorectal and Ovarian Cancer Screening project team compared the fiber intakes of 34,000 subjects without colon polyps.

Experts say while these results are encouraging, this research still does not prove how fiber prevents colon cancer or if fiber works alone.

Other health habits?

However, many other studies show a spectrum of answers, baffling researchers and consumers alike.

"It's hard to pinpoint fiber alone as a factor. This is probably because diets high in fiber are high in many other potentially protective factors such as folate and other vitamins. Also, people who consume high fiber diets also tend to follow other healthy lifestyle behaviors by exercising and not smoking," says Marjorie McCullough, D.Sc., R.D., an epidemiology researcher at the American Cancer Society.

People with high-fiber diets are also more likely to eat less red meat, drink less alcohol, smoke less and get regular exercise - all healthy behaviors that can reduce any kind of cancer risk.

Previous studies looking solely at fiber and colon cancer say dietary fiber may not be the magic ingredient that reduces the risk of colorectal cancer and adenomas. A major 1999 report, published in the New England Journal of Medicine, looked at 88,000 women participating in the Nurses' Health Study. The women were followed for 16 years. Little, if any, link between reduced colon cancer risk and fiber consumption existed. Also, studies from Finland and Sweden have found no protective effect from fiber.

Traditionally, researchers have several reasons for thinking fiber would protect against colon cancer, McCullough says. One theory suggests that by binding carcinogens and reducing constipation fiber might reduce the time that carcinogens interact with cells in the colon. Another theory suggests certain compounds produced in the colon when fiber is eaten may be healthy for colon cells.

"If you look at the EPIC study, you'll see that the association with fiber and colon cancer is not enormously strong," says Joel Weissfeld, M.D., associate professor in the Department of Epidemiology of the University of Pittsburgh Medical Center. He explains the study does not address the differences of diets in varying cultures and the mixture of fiber. Fiber is found in whole grains, cereals with ingredients like bran, beans, fruits and vegetables. Generally, the European study was high in grains and cereal.

"The question is: How much fiber is protective, and what kind of fiber would that be?" he says, noting that eating more than the recommended amount of 30 grams of fiber a day does not show an additional benefit.

It could be that fiber intake doesn't do much by itself. Consuming calcium could be a link in helping to prevent colon cancer. Also, people following healthy diets and regular exercise tend to have lower glycemic levels.

"We don't know how much of a role dietary fiber plays in preventing colon cancer or if there are other factors. There will always be that uncertainty. When you are dealing with complex diseases like colon cancer, there may not be one cause or one intervention. Which factor it may be, we may never know."

Eating habits, not pills

Supplements may not be that magical elixir either.

Another study by the European Cancer Prevention Organization Study Group and published in a 2000 issue of The Lancet, researchers gave fiber supplements, calcium supplements or placebo (a sugar pill) to 552 people who earlier had precancerous polyps surgically removed from the colon. After three years on fiber supplements, the patients were checked for new polyps. At least one new polyp was found in 29 percent of those getting the fiber supplements, compared with 20 percent of those getting the dummy supplements, making those getting the fiber supplements about one-third more likely to develop new polyps. About 16 percent of study participants who took calcium supplements developed new polyps.

No matter what, experts stress that supplements for fiber intake are not the way to go. You are far better off getting fiber the natural way - from your diet.

"We want a diet that is plant-based and contains a whole arsenal of nutrients and phytochemicals such as lycopene and lutein," says Melanie Polk, M.M.Sc., R.D., F.A.D.A., consultant at the American Institute for Cancer Research (AICR).

Consuming too much alcohol, fat or calories and too little carotenoids, fiber and vitamin C may cause an increased risk for all cancers. An estimated one-third of all cancers may be diet-related, according to AICR. And it's never too late to start including nutrient-rich plant foods in your diet, McCullough says.

"If a 65-year old man started increasing his intake of plant foods, - which are also high in fiber - such as fruits, vegetables and whole grains, his risk of developing certain cancers and cardiovascular disease would be reduced compared with someone who did not change their diet," McCullough says.

Fiber is healthier

Whether or not fiber has direct cancer-preventive effects, it's still good for you. Here are some ways that The American Institute for Cancer Research says fiber helps the body.

• Dietary fiber slows the absorption of food. This helps keep blood sugar level and insulin steady and satisfies appetites longer.

• By lowering cholesterol absorption from food and reducing cholesterol production by the body, dietary fiber may help protect the cardiovascular system.

• As the colon tries to digest fiber, substances are produced that regulate the growth of cells lining the colon. A regular pattern of cell growth is healthy; cancerous cells grow unchecked, out of control.

• By collecting and holding damaging bile acids, fiber protects the lining of the colon.

• By increasing stool bulk and weight, fiber dilutes harmful substances and speeds up their elimination from the body. This action also helps prevent constipation.

To get more fiber:

Melanie Polk of the American Institute for Cancer Research offers some tips for food choices.

• Bring healthy snacks to work so you won't be tempted by the vending machine. Pack an apple or some celery with peanut butter.

• Read the ingredients on the label. Generally, the more ingredients, the less likely something is good for you. "Highly processed foods tend to be low in dietary fiber," Polk says. "If there is a long list of things, think twice. The shorter the list, the better."

• Give your body some time to adjust to increasing your fiber intake. Go slowly.

• Aim for at about 9 to 13-ounce glasses of water or other beverages without caffeine each day.

• Choose whole grain breads and any foods with bran in them.

• Fill at least two-thirds (or more) of your lunch and dinner plates with vegetables, fruits, whole grains and beans - especially vegetables and fruits - and one-third or less with lean meat and dairy. This kind of diet is naturally low in fat and calories and high in vitamins, minerals, phytochemicals and dietary fiber.

Related Articles Cancer Prevention: The New Evidence Fiber Facts: The Trick to Understanding Labels

External Sources American Institute for Cancer Research American Cancer Society National Cancer Institute Dollinger M, Rosenbaum, EH, Tempero M., et al. Everyone's Guide to Cancer Therapy, Fourth Edition, Kansas City, Missouri: Andrews McMeel Publishing, 2002 Rosenbaum, EH, Rosenbaum, I, Everyone's Guide for Supportive Cancer Care, Fourth Edition, Kansas City, Missouri: Andrews McMeel Publishing, 2005

This article was reviewed and updated June 2007.

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