Fiber does a lot more than just ensure bowel regularity — it has positive effects on the rest of the body, and the mind as well.
Found in plant foods, fiber passes through the gastrointestinal tract largely undigested. The complex carbohydrate comes in two varieties, soluble (which partially dissolves in water) and insoluble, often found in the same foods. While it may seem odd to attribute health benefits to a carb you can’t absorb, fiber boasts anti-inflammatory properties that can boost immune responses, besides playing several important roles in the digestive and cardiovascular systems.
Researchers are cautious about ascribing some study results to fiber alone, since foods rich in fiber — whole grains, legumes, fruits, vegetables, nuts, and seeds — are also sources of so many vitamins, minerals, and antioxidants that are critical to good health. Because of this synergy, the American Dietetic Association recommends that we seek our daily allowance of fiber — 20 to 35 grams — from foods as much as possible before turning to supplements.
Here are eight ways fiber contributes to your well-being and some tips to get more fiber in your diet.
1. Cholesterol/Heart disease
Soluble fiber helps lower total blood cholesterol and low-density lipoprotein, or "bad," cholesterol levels, along with triglycerides. It binds with bile acids, which are responsible for breaking down fats, in the intestinal tract, allowing them to be excreted. The body replaces lost bile acids by synthesizing them from blood cholesterol, reducing levels in the bloodstream.
Cholesterol is a factor in atherosclerosis, the accumulation of plaque that causes the coronary arteries to harden and narrow, increasing blood pressure and the risk of heart attack from total blockage. A Harvard study of more than 40,000 male health professionals linked a high total dietary fiber intake to a 40 percent lower risk of coronary heart disease, compared to a low fiber intake; findings were similar in a study of female nurses. The Food and Drug Administration allows producers of foods that contain specified amounts of soluble fiber from oats, barley, and psyllium husk to claim that eating them may reduce the risk of heart disease.
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2. Diabetes
Fiber intake appears to stabilize blood sugar levels and lower insulin demand by various mechanisms, including slowing absorption of nutrients during digestion. In clinical studies, diets high in fiber are associated with a reduced incidence of Type 2 diabetes — the most common form of the disease, which occurs when the body becomes resistant to insulin, the hormone that signals tissues to take glucose from the bloodstream. Eventually this can lead overstimulated insulin-producing cells to cease functioning. But even insulin-dependent Type 1 diabetes responds to fiber: The journal Diabetologia reported a study in which Type 1 diabetes patients who ate 50 grams of fiber a day for 24 weeks significantly improved glycemic control.
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3. Brain power
Because the brain runs on glucose, keeping blood sugar levels constant enhances mental acuity and alertness. Fiber-rich foods tend to be low on the glycemic index — that is, they raise blood sugar levels gradually as food is digested, unlike high-glycemic-index foods, which cause spikes and subsequent drops. A study at Cardiff University in Wales, reported by BBC News, found a 10 percent reduction in fatigue, lower depression scores, and better cognitive powers among participants whose breakfasts included a high-fiber cereal. A Tufts University study found that children who ate oatmeal for breakfast scored better on tests of cognitive performance than those who ate processed cereal (or no breakfast at all). One of the study’s co-authors, Quaker Oats nutrition research director Priscilla Samuels, credited “oatmeal’s whole grain, high fiber, and protein attributes.”
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4. Bowel health
Fiber has long been heralded as a cure for constipation. Also known as roughage or bulk, fiber adds volume and softness to stools, making peristaltic contraction of the colon more productive in moving the solid matter along. Soluble fiber acquires a gelatinous texture in the intestine when combined with water; insoluble fiber remains intact as it soaks up water and expands. Because of its solidifying and water-absorbing actions, fiber can also relieve certain types of diarrhea.
Fiber also protects against the development of hemorrhoids and diverticula — pouches in the colon wall that can become inflamed or infected, leading to painful diverticulitis. Nearly half of all Americans over age 60 have diverticula, a condition more common with age; 10 to 25 percent of them will develop diverticulitis, according to the Journal of Clinical Gastroenterology. The Harvard School of Public Health cites a study showing that dietary fiber was associated with about a 40 percent lower risk of diverticular disease, and fiber is also used to treat its symptoms. Numerous studies link fiber with alleviating other inflammatory diseases of the bowel, such as colitis.
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5. Cancer
An analysis of 13 studies, reported in the Journal of the National Cancer Institute, found “substantive evidence that intake of fiber-rich foods is inversely related to risk of cancers of both the colon and rectum.” The authors estimate that the risk of colorectal cancer in the United States could be cut by 31 percent with a 13-gram-per-day hike in fiber from food sources (an average increase of about 70 percent). Preliminary clinical evidence also suggests that a diet high in fiber (combined with lifestyle changes and conventional medication) may help protect against other types of cancer such as prostate, breast, and lining of the uterus, according to the University of Maryland Medical Center.
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6. Weight control
“A fiber-rich meal is processed more slowly, which promotes earlier satiety, and is frequently less calorically dense and lower in fat and added sugars,” says the American Dietetic Association — all characteristics of a dietary pattern to treat or prevent obesity. To put it another way, because fiber-rich foods frequently have more volume (and nutrients) relative to their calories, it takes longer to eat and digest them; you feel full sooner and stay full longer. Fiber’s normalizing action on blood glucose and insulin levels may also help dieters curb the cravings and energy crashes that fuel overeating.
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7. Lung disease
High fiber intake, especially from whole grains, is associated with a lower risk of chronic obstructive pulmonary disease (COPD), an umbrella that includes emphysema and chronic bronchitis. The findings come from a study of more than 100,000 U.S adults followed for 16 years; when researchers factored in smoking and other lifestyle data, the group that consumed the most dietary fiber — 28 grams per day — had a one-third lower risk of COPD than those with the least fiber. The report in the American Journal of Epidemiology noted the antioxidant and anti-inflammatory properties of fiber could affect the development of chronic lung disease.
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8. Immune response
The interaction of certain kinds of friendly intestinal bacteria with fiber gives rise to compounds called short-chain fatty acids, which have a beneficial effect on the immune system and its ability to reduce inflammation. “If we have low amounts of dietary fiber, then we’re going to have low levels of short-chain fatty acids, which we have demonstrated are very important in the immune systems of mice,” says Kendle Maslowski, co-author of a study by the Garvan Institute of Medical Research in Sydney, Australia. The authors suggest that this mechanism may have implications not just for digestion-linked diseases such as diabetes and colitis, but for inflammatory ailments elsewhere in the body, such as asthma and rheumatoid arthritis.
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Fiber-full foods
Adding legumes to your plate is a very effective method of boosting fiber, according to the Mayo Clinic — consider split peas (16.3 grams per cup, cooked), lentils (15.6 grams), black beans (15 grams), lima beans (13.2 grams), or baked beans (10.4). A single artichoke has 10.3 grams of fiber; if you’re eating vegetables by the cup, peas boast 8.8 grams of fiber, broccoli has 5.1 grams, turnip greens have 5 grams, corn has 4.2 grams, and brussels sprouts have 4.1.
Among fruits, raspberries reign, with 8 grams of fiber per cup. A medium pear (with skin) has 5.5 grams; an apple (with skin) has 4.4. Bananas and oranges have 3.1 grams each; a 1.25-cup serving of strawberries has 3.8. In the grain/cereal group, look for whole-wheat spaghetti, with 6.2 grams of fiber per cup, cooked; pearled barley, with 6 grams, ditto; 5.3 grams in three-quarters of a cup of bran flakes; 4 grams in a cup of oatmeal; 3.5 grams in three cups of air-popped popcorn or a cup of brown rice. Whole-wheat, multigrain, or rye breads contain 1.9 grams per slice. In the nuts and seeds category, a quarter-cup of sunflower kernels contains 3.9 grams, and one-ounce servings of almonds, pistachios, and pecans have 3.5, 2.9, and 2.7 grams, respectively.
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Diet strategies
Swap whole-grain products for refined ones whenever you can; processing removes the germ and bran portion of the grain, where most of the fiber resides, leaving only the endosperm, says the University of Florida’s Institute of Food and Agricultural Sciences. Look for breads, cereals, baked goods, and pasta that contain substantial proportions of whole wheat or whole grain; if you do your own baking, experiment with replacing some of the white flour with rye flour, oatmeal, oat bran, or wheat.
Substitute brown rice for white rice. Try an orange instead of juice for breakfast, or slice fruit into your (whole-grain) cereal. Add wheat germ or bran to cereal; add beans to soups, salads, and stews. Choose fresh fruit instead of a sugary dessert, and keep bite-sized vegetables or whole-wheat crackers handy for snacking. Don’t do it all at once, though: Increase your fiber intake gradually to allow your body to adjust, and drink plenty of water (at least 8 cups daily).