There's more good news. You don't have to force yourself to eat massive quantities of unpleasant foods. The full-body benefit comes from eating the 20-35 grams of fiber per day recommended by dietary guidelines.
Now nutritionists have even more reason to stress the importance of fiber, says Leslie Bonci, MPH, RD, director of sports nutrition at the University of Pittsburgh Medical Center. She was not involved in the study.
"When people think fiber, they think gut -- it is just having an effect on the lower part of my body," Bonci tells WebMD. "But now it is very exciting to realize that fiber is having an effect in the upper body, too. Fiber is a head-to-toe body benefit. People need it."
Fiber for Heart Health
Yunsheng Ma, MD, PhD, of the University of Massachusetts Medical School in Worcester, followed 524 healthy adults for one year. At the beginning of the study -- and every three months -- the researchers drew blood for lab tests and collected details about what the volunteers were eating.
Most of the study participants were getting far less fiber than they should. They averaged only 16 grams of fiber a day. The 20% of study subjects who ate the least fiber got a little more than 10 grams a day. The 20% who ate the most got more than 22 grams a day -- within recommended levels.
Compared with those who ate the least fiber, those who ate the most were 63% less likely to have high levels of C-reactive protein (CRP). Although this relationship was stronger than other studies, consistently high CRP levels have been shown to predict an increased risk of heart disease and stroke. High CRP levels are also a sign that a person is at risk of diabetes.
Ma's study appears in the April issue of the American Journal of Clinical Nutrition.
Fiber Fights Diabetes in Overweight/Obese People
People who are overweight are at an increased risk of type 2 diabetes, the most common kind. Fiber might help, suggests Martin O. Weickert, MD, of the German Institute of Human Nutrition in Nuthetal, Germany. Weickert noted that people who eat a lot of cereal fibers, such as bran, are less likely to get diabetes.
His research team studied 17 overweight or obese women. For three days, three times a day, the women ate some white bread. Half the women got plain white bread. The other half got bread spiked with 10.4 grams of oat fiber.
Over time, the bodies of overweight people become less and less sensitive to insulin, the hormone that controls blood sugar levels. This lack of sensitivity results in diabetes in some people. Weickert and colleagues found that the women who ate the oat fiber over the short three-day time period became significantly more sensitive to insulin.
What's going on? Cereal fiber is also called insoluble fiber. It can't be digested, but it does give bulk to the stool. That's good in and of itself. But Weickert suggests that increased insoluble fiber leads to more fermentation at the lower end of the bowels. This might set off a chain reaction that changes the way their body responds to insulin.
The molecular mechanisms leading to improved insulin sensitivity after consumption of insoluble cereal fibers are not clear at present," Weickert tells WebMD.
He's planning a larger clinical trial to answer this and other questions.
Weickert's study appears in the April issue of Diabetes Care.
Where to Find Fiber
People need both insoluble fiber and soluble fiber, Bonci says.
"You have to mix it up. Don't put all your bran in one box," she says. "Foods tend to have both. Apples, for example, have insoluble fiber in their skins and soluble fiber in their flesh. So foods are a better way to get fiber than supplements. You get the whole package with foods."
Foods with a lot of soluble fiber include:
- Nuts and seeds
- Legumes (peas, beans, and lentils)
Foods packed with insoluble fibers include:
- Whole-grain bread
- Whole-grain breakfast cereals
- Wheat bran
- Many vegetables, including carrots, cucumbers, zucchini, celery, and tomatoes