Think about what you ate yesterday. How many high-fiber foods did you have? If you’re like most Americans, probably not enough. Our typical diets include only about 10 to 15 grams of dietary fiber a day, but the Daily Value is 25 grams. For many of us, that means doubling our current intakes. For more than two decades, scientists have been taking a close look at fiber and its potential health benefits. What they’ve found is that high-fiber diets may decrease the risk of colon and breast cancer, ease constipation and irritable bowel syndrome, and help prevent diverticulosis, hemorrhoids, high cholesterol, and diabetes.
Nature’s Glue, Nature’s Sponge
Fiber is the indigestible part of all plant foods, including fruits, vegetables, grains, and beans. It is not found in meat or any other animal foods. Most fiber-rich foods contain both soluble and insoluble fiber. Soluble fiber dissolves in water in your intestinal tract, forming a gluelike gel. It softens stools and slows down stomach emptying, allowing for better digestion and helping you feel fuller longer, an effect that may aid weight loss.
Soluble fiber has been credited with lowering blood cholesterol. It may also help people with diabetes by lowering the amount of insulin necessary to process blood sugar after a meal. When taken with plenty of water before meals, a soluble fiber supplement binds with water in the stomach and forms a gummy mass—and that’s what makes us feel full.
Insoluble fiber is the champion of the gastrointestinal tract. It’s a good natural laxative because it holds onto water and moves waste quickly through the intestines, says David Beck, M.D., chairman of colon and rectal surgery at the Ochsner Clinic in New Orleans. It also adds bulk and softens stools.
In general, soluble fibers are found in higher concentrations in fruits, oats, barley, and beans. When shopping for soluble fiber supplements, you can choose from psyllium, gums, mucilages, glucomannan, or pectins, says Dr. Beck. Insoluble fibers are more abundant in vegetables, wheat, and cereals; supplements include wheat bran and flaxseed.
Although it’s helpful to classify fiber as either soluble or insoluble, we need both kinds in our diets. And fibers don’t always fit neatly into categories. Psyllium, for example, which is a soluble fiber, promotes bowel movements, a benefit usually associated with insoluble fiber. And rice bran, an insoluble fiber, lowers blood cholesterol, which is a trait of some soluble fibers.
Moving Things Along
Some studies have shown a link between high-fiber diets and a decreased risk of colon cancer, says Dr. Beck. Since fiber increases the bulk of the stool, it may dilute cancer-causing substances there. It also moves waste faster through the digestive tract, leaving less time for potentially harmful or even cancerous substances in your stool to have contact with the lining of the bowel, he says.
SUPPLEMENTSNAPSHOT
| Fiber Supplement forms: Psyllium, gums, mucilages, glucomannan, pectins, methylcellulose, calcium polycarbophil, flaxseed, and brans. May help: Colon cancer, breast cancer, heart disease, diverticulosis, hemorrhoids, constipation, diabetes, overweight, Parkinson’s disease, irritable bowel syndrome, indigestion, high blood pressure, and high cholesterol. Daily Value: 25 grams. Special instructions: Do not take with food; always drink at least eight ounces of water for each tablespoon of fiber that you take. Who’s at risk for deficiency: Many Americans; average consumption is only 10 to 15 grams a day. Good food sources: All plant foods. The best sources include wheat-bran cereals, beans, dried figs, peas, raspberries, bulgur, oatmeal, pears, sweet potatoes, oranges, apples, and barley. Cautions and possible side effects: Do not take if you have trouble swallowing. Talk to your doctor before taking any fiber supplement, especially if you have diverticulitis, ulcerative colitis, Crohn’s disease, bowel obstruction, or any other serious gastrointestinal disorder or if you are taking any medications. May cause bloating or constipation. |
Fiber, particularly insoluble fiber, is also thought to help prevent hemorrhoids and diverticulosis, a condition in which small sacs develop in weak areas of the intestinal wall. It does so by softening stools and speeding up the movement of waste through the intestinal tract.
Fiber may also help ease the symptoms of irritable bowel syndrome, a condition characterized by alternating constipation and diarrhea, gas, and cramps.
While much research has focused on the link between fiber and gastrointestinal health, studies also show that dietary fiber may protect against breast cancer, according to David P. Rose, M.D., Ph.D., D.Sc., chief of the division of nutrition and endocrinology for the American Health Foundation in Valhalla, New York. High intakes of fiber have been shown to reduce estrogen levels in the blood, he says. That’s important because high levels of estrogen are associated with increased breast cancer risk.
Fiber may reduce estrogen by binding with it in the intestine before carrying it out of the body in the stool. Fiber may also help prevent the reabsorption of estrogen in the blood.
Help for the Heart
Studies have shown that people who get the most fiber in their diets are less likely to have heart disease.
In a Finnish study of nearly 22,000 male smokers ages 50 to 69, men who ate the most fiber, averaging 35 grams daily, suffered one-third fewer heart attacks than those who ate the least fiber. To look at it another way, each 10 grams of fiber added to the diet decreased the risk of death from heart disease by 17 percent.
In a study of 44,000 male health professionals, those who ate more than 25 grams of fiber a day had a 36 percent lower risk of developing heart disease than those who ate less than 15 grams daily.
Soluble fiber gets a big chunk of credit for helping the heart because it’s repeatedly been shown to lower blood cholesterol levels. It does so in several ways, says Tom Wolever, M.D., Ph.D., professor of nutritional sciences and medicine at the University of Toronto. When we fill up on fiber, there is less room for high-fat, high-cholesterol foods. In fact, a growing number of studies show that a diet rich in soluble fiber will lower blood cholesterol levels by 6 to 8 percent, he says.
Soluble fiber has another cholesterol-lowering effect, Dr. Wolever says. It binds with bile acids, which affects the way the liver handles blood cholesterol. As a net result of this process, cholesterol levels go down.
This cholesterol-lowering effect of fiber seems to be limited to specific foods and supplements that contain a generous amount of soluble fiber, including pectin, guar gum, psyllium, oat bran, oatmeal, and legumes.
Do You Need a Fiber Supplement?
Health experts generally recommend that you get your fiber from food, not supplements, because food contains nutrients that supplements don’t.
"I don’t often prescribe fiber supplements, because I want people to change to a whole-foods diet," says William D. Nelson, N.D., a naturopathic doctor at the Docere Naturopathic Centre in Colorado Springs. Patients who switch from processed and fast foods to whole foods, including whole grains, fresh vegetables, fruits, and beans, usually don’t need supplemental fiber, he says.
Sometimes, though, we can’t or won’t get all the fiber we need. That’s when supplements can help, says Dr. Beck. "Most of us are very busy. Fiber supplements allow us to worry less about what we’re eating."
Whether you’re adding more fiber-rich foods to your diet or taking fiber supplements, you need to increase your intake gradually. Since fiber isn’t absorbed, it can ferment in the intestine, causing gas, bloating, cramps, and diarrhea.
Always drink at least eight ounces of water with a fiber supplement, advises Dr. Beck. Fiber acts like a sponge, and if you don’t drink plenty of fluids, it can swell and block part of the gastrointestinal tract. It can also block the esophagus, so experts recommend avoiding fiber supplements if you have trouble swallowing.
Too much fiber can block the absorption of minerals such as iron, calcium, and zinc. It could also cause calcium losses.
If you supplement, try to get your fiber from a variety of sources in addition to a high-fiber diet. Look for products like psyllium, apple and grapefruit pectin, guar gum, methylcellulose, and calcium polycarbophil. At your local health food store, you may also find wheat and oat bran tablets and multifiber tablets with ingredients like beet and carrot fibers.
Psyllium is a popular and inexpensive fiber supplement with a laxative as well as a cholesterol-lowering effect, says Dr. Nelson. This supplement is available in pill, capsule, or powder form. All forms are equally effective, but fiber capsules and tablets are more expensive than powders.
If you’re taking a tablet or capsule, you have to take as many as 10 to get the same amount of fiber you’d find in a tablespoon of psyllium seed powder, says Jennifer Brett, N.D., a naturopathic doctor at the Wilton Naturopathic Center in Stratford, Connecticut. With so many pills to take, people tend to abandon them more quickly than they do powder supplements.
Psyllium causes gas and bloating in some people. If that happens to you, try flaxseed, which is easiest to take in capsules or in powdered form. In addition to fiber, flaxseed contains lignans, compounds that may have anti-cancer, antibacterial, antifungal, and antiviral effects, says Dr. Nelson.
Be leery of marketing claims that fiber supplements containing chitosan (a form of chitin, which is a component of the shells of shellfish) promote weight loss, says Dr. Brett. "I’ve never seen any evidence that it works for weight loss," she says. Even if chitosan did remove fat from the body as its proponents claim, it would also bind with and remove fat-soluble vitamins that your body needs, she says.
Animal studies have shown that chitosan can absorb LDL cholesterol (the bad type) and reduce lipid concentrations, but further studies are needed to confirm any cholesterol-lowering action. As for a weight-loss effect, some animals in the studies actually gained weight when they were fed chitosan, while others lost.
