Dietary Fiber and Mortality

Scientists have proven that dietary fiber lowers the risk of coronary artery disease, diabetes and certain cancers. Surprisingly however, they had yet to show that fiber could impact overall mortality. Now apparently, they have done just that.

A research team led by Yikyung Park of the National Cancer Institute has published a study showing that higg fiber intake is indeed associated with longer survival.

To reach these conclusions, Park’s group looked at data from nearly 400,000 men and women between the ages of 50 and 71 using the AARP Diet and Health Study. They assessed dietary fiber intake with a questionnaire administered at the beginning of the 9-year follow-up study. They excluded people with diabetes, heart disease and most cancers, as well as those who reported extremely high daily fiber intake.

After controlling for smoking, exercise and body weight, the researchers showed that dietary fiber intake was associated with a reduced risk of death in both sexes.

Specifically, people in the highest quintile for fiber consumption (29.4 grams per day for men and 25.8 grams for women) were 22% less likely to die from any cause than those in the lowest quintile (12.6 grams per day for men and 10.8 for women). Women were 34-59%, and men were 24-56%  less likely to die from heart, respiratory and infectious diseases, in particular. Fiber consumption was associated with a lower risk of dying from cancer in men (who are prone to get cancers thought to be reduced by dietary fiber intake) but not in women.

Interestingly, the type of fiber consumed made a huge difference in this study. Participants who consumed fiber from grains, like oatmeal, brown rice and cornmeal experienced all the benefits. In this study at least, fiber derived from vegetables, fruits and beans did not reduce mortality.

“Whole grains are rich sources of fiber, but also good sources of vitamins, minerals, and other phytochemicals that may provide health benefits,” Park explained in an interview. It’s also true that grains have anti-inflammatory and antioxidant properties, which could have been decisive. (It’s important to add that many prior studies have shown that diets rich in fiber from fruits and vegetables can reduce cardiovascular risk.)

The mechanisms by which fiber cuts mortality risk remain unclear. In addition to its anti-inflammatory and antioxidant effects, fiber reduces LDL (bad) cholesterol and normalizes blood glucose levels. It may also bind to cancer-causing agents in the gut, thereby preventing them from being absorbed into the body.

Note: The federal government’s new Dietary Guidelines for Americans suggest that women consume 25 grams of fiber per day, and that men consume 38 grams per day. The average American consumes about 15 grams per day. Given what appears to be differential effects of fiber from different sources, it’s wise to get your fiber from as wide a variety of sources as possible, including fruits, vegetables, grains and legumes.

The study appears in the Archives of Internal Medicine.