Why You Need More Fiber

High-fiber foods boost health and help control your weight

By Elaine Magee, MPH, RD
WebMD Weight Loss Clinic - Feature

Reviewed By Louise Chang, MD

Most of us haven't a clue how many grams of fiber we get from our diets in on a typical day. Yet for many Americans, this number should be doubled.

A recent American Dietetic Association position paper reported that most of us don't even come close to the recommended intake of 20 grams to 35 grams of fiber a day. Americans' mean fiber intake is about half that --14-15 grams a day.

That's not surprising when you consider that we get fiber from 'roughage' like fruits, vegetables, whole grains, nuts/seeds, and beans. The typical American isn't exactly loading his or her plate with these foods (you'd be hard-pressed to find a fruit, vegetable, whole grain, or bean in your average fast-food value meal).

Why Is Fiber so Good for Us?

Eating a higher-fiber diet has been shown to lower blood cholesterol levels, improve and prevent constipation, and slow digestion. And according to Barbara Rolls, PhD, author of The Volumetrics Eating Plan, fiber can help us eat less -- and lose weight.

"Simply doubling the amount of fiber you eat from the average of 15 grams per day to around 30 grams helps reduce calorie intake," Rolls explains. "Fiber has been shown to increase satiety, not only by lowering the energy density of foods (that is, how many calories they have per serving) but also by slowing the rate that foods pass through the digestive systems."

When you increase dietary fiber, do it gradually to avoid gastric distress, and to drink plenty of fluid (8 cups per day) to avoid constipation.

Joanne Slavin, PhD, an obesity researcher with the University of Minnesota, says dietary fiber not only makes us feel fuller, but reduces digestibility. Some studies have shown that large amounts of fiber in the diet can help regulate blood glucose and insulin. These may be reasons why people who eat higher-fiber diets tend to weigh less and are less prone to gain weight as they age.

"The best protection is at the highest fiber intakes -- at least 25 grams a day recommended for women," says Slavin.

The research findings on fiber's benefits keep pouring in. Some recent studies have shown that:

  • Eating a higher-fiber diet, as part of an overall healthful lifestyle, may play a role in a healthful BMI (body mass index). One study found that women who ate more whole grains and total fiber consistently gained less weight over 12 years than those who ate less fiber and whole grains. Another study found that women with low-fiber, high-fat diets were more likely to be overweight than those following high-fiber, low-fat diets. "Weight control advice for American women should place greater emphasis on consumption of fiber," notes one of the study's researchers, Megan McCrory, PhD.
  • A high-fiber diet may reduce your risk of colon cancer. If populations with a low average fiber intake suddenly doubled their fiber by making wiser food choices, they could lower their risk of colon cancer by 40%, according to a study involving data collected from 10 European countries. A recent National Cancer Institute study also linked high fiber intakes to a lower risk of colorectal cancer. This was especially true for fiber from grains, cereals, and fruits.
  • Fiber may reduce the risk of type 2 diabetes. Those who ate a diet high in refined carbohydrates and low in cereal fiber were more likely to increase their risk of type 2 diabetes, according to a recent study. And a recent Finnish study showed that as whole grain and cereal fiber intake increased, the risk of type 2 diabetes seemed to decrease. But it may not just be all about the fiber in this case; high-fiber foods are also rich in important micronutrients. That's why it's better to concentrate on including whole plant foods in your diet than to take a fiber pill or supplement.

Fiber intake has also been linked to the metabolic syndrome, a cluster of risk factors that increase the chances of developing heart disease and diabetes:

  • Higher intakes of fiber (from cereal and whole-grain products) were linked with a slower build up of cholesterol filled plaque of the arteries in postmenopausal women with coronary artery disease. In another study, in men and women aged 40-60 and free of heart disease, viscous fiber (especially pectin, the type of soluble fiber found in apples) appeared to protect against the progression of atherosclerosis in neck arteries.
  • High intakes of oat fiber appeared to have a protective effect on the heart, by lowering LDL "bad" cholesterol without decreasing HDL "good" cholesterol.

The 2 Types of Fiber

Though both have health benefits, there's a difference between the insoluble, type of fiber found in whole grains, carrots, tomatoes, and lettuce, and the softer, water-soluble type found in oatmeal, pears, strawberries, and apples.

Soluble or viscous fiber is the softer type that dissolves in water.

When digested, it helps prevent cholesterol from being absorbed in the intestines. This type of fiber is also thought to help minimize the rise in blood sugar levels after a meal, which is particularly helpful for people with diabetes.

This type of fiber comes from: beans (they have both types of fiber), oatmeal and oat bran, some fruits (apples, mangoes, plums, kiwi, pears, blackberries, strawberries, raspberries, peaches, citrus fruits, dried apricots, prunes, and figs), and some vegetables (dried peas, beans, and lentils).

Insoluble fiber doesn't dissolve in water.

It helps keep bowel movements regular, and may reduce the risk of colon problems. It may also reduce the risk of hemorrhoids, varicose veins, and obesity (by making us feel full).

Insoluble fiber is found in: Whole-wheat grain and wheat bran, brown rice, bulgur, seeds, and vegetables (carrots, cucumbers, zucchini, celery, and tomatoes).

Do you need to measure how much of each type of fiber you get in your diet? Don't worry about it. Some foods offer both types of fiber, and not all soluble fibers block absorption of cholesterol. In fact, according to the American Dietetic Association, the National Academy of Science has recommended phasing out the terms "soluble" and "insoluble" when discussing fiber. The bottom line: All dietary fiber is good for you. Just get more of it.

Your next step? Check out 6 Foods and Tips for More Fiber.

Medically Updated: May 19, 2006.

SOURCES: Journal of the American Dietetic Association, September 2005. American Journal of Clinical Nutrition, August 2002, March 2003, November 2003, December 2003, and August 2004. American Heart Journal, July 2005. U.S. Department of Agriculture Nutrient Database. ESHA Food Processor II. Barbara Rolls, PhD, author, The Volumetrics Weight-Control Plan and The Volumetrics Eating Plan; and professor, nutritional sciences, Pennsylvania State University, State College, Pa. Joanne Slavin, PhD, RD, nutrition researcher, University of Minnesota, St. Paul, Minn. Megan McCrory, PhD, research associate professor, School of Nutrition and Exercise Science, Bastyr University, Kenmore, Wash. American Dietetic Association.

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Last Editorial Review: 5/19/2006