What is Fiber?
by Dr. Gary Farr on 25 November 2001
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Types of Dietary Fiber: Water Soluble Fiber; Soluble Fiber; Water Insoluble Fiber; Insoluble Fiber; Pectins; Gums; Mucilages
What it is: Given all the media hype about fiber, you'd assume it was a vital {gl_nutrient}NUTRIENT. You'd be wrong. Although classified as a {carbs} CARBOHYDRATE, fiber supplies no {gl_vitamin} VITAMINS, {gl_minerals} MINERALS or even {gl_calorie} CALORIES. It does, however, play important roles in the body. Basically, there are two types of fibers: those that dissolve in water (water-soluble or, more simply, soluble fiber) and those that don't (water-insoluble or insoluble fiber). The water-soluble fibers - {gl_pectin} PECTINS, {gl_pectin} GUMSand mucilages — are found mainly in citrus fruits, apples, potatoes, dried peas and beans, oatmeal and oat {gl_bran}BRAN. In the body, they bind bile acids (the liver synthesizes these out of {gl_cholesterol} CHOLESTEROL), and as the acids are bound, cholesterol is withdrawn from the blood and converted to bile acids to replace the deficit. The cholesterol-lowering effect may be subtle; still, it reduces the risk of heart disease. Water-soluble fiber also lowers — or at least stabilizes — blood sugar {gl_glucose} GLUCOSE) levels. And that's good news for diabetics. Intricately bound to digestible carbohydrates, which the body breaks down to form glucose, fiber acts like a brake, slowing the digestion of carbohydrates and subsequent release of glucose into the blood.
The two most common water-insoluble fibers, {gl_cellulose} CELLULOSE and lignin, form the framework of plant cell walls. Neither cellulose (found in wheat bran, whole wheat, whole-grain breakfast cereals, broccoli and carrots) nor lignin (asparagus, wheat bran and pears) will dissolve in water, but both have the ability to absorb it. This means they bulk up stools and speed the passage of waste through the intestines, functions believed to reduce the risk of colon cancer.
If you haven't been eating enough fiber, it's wise to increase your intake slowly. Doing so all at once can cause gas, bloating, diarrhea. It's also important to drink plenty of water when eating lots of fiber. Otherwise, you may irritate, even block your digestive tract.
So how much fiber is enough? There is no {gl_rda} RDA for fiber, but most nutritionists recommend 20 to 35 grams of fiber a day (most Americans get no more than 10 to 13 grams). They also recommend that you include both the water-soluble and water-insoluble fiber in your diet. No problem if you regularly eat a wide variety of fruits, vegetables and whole-grain breads and cereals.
Note: Many grains, brans, fruits and vegetables contain both types of fiber. But no animal food (meat, eggs, milk, cheese, etc.) provides any fiber whatsoever.
Food Serving Size Total Fiber (gms) Soluble Fiber (gms) Insoluble Fiber (gms) Fruits Apple, with skin 1 medium 2.7 1.0 1.7 Banana 1 medium 2.3 0.7 1.6 Grapes 1 cup 0.6 0.1 0.5 Orange 1 medium 2.5 1.6 0.9 Pear, Bartlett 1 medium 4.0 0.8 3.2 Prunes, dried 4 3.1 1.3 1.8 Strawberries 1 cup 1.6 0.6 1.0 Vegetables Beans, green, cooked 1/2 cup 2.0 0.8 1.2 Broccoli, raw 1/2 cup 1.5 0.1 1.4 Brussel Sprouts, Cooked 1/2 cup 3.6 1.7 1.9 Carrot, raw 1 medium 2.6 1.1 1.5 Cauliflower, raw 1/2 cup 1.0 0.4 0.6 Celery, raw 1/2 cup 0.9 0.2 0.7 Corn, cooked 1/2 cup 4.7 0.2 4.4 Lettuce, Butterhead 1 cup 1.3 0.6 0.7 Lettuce, Iceberg 1 cup 1.0 0.3 0.7 Lettuce, Romaine 1 cup 0.7 0.3 0.4 Peas, cooked 1/2 cup 4.4 1.2 3.2 Pepper, green, raw 1/2 cup 0.9 0.3 0.6 Potato, with skin 1 medium 2.4 0.6 1.8 Sweet potato, peeled 1 medium 3.4 1.7 1.7 Tomato 1 medium 1.3 0.3 1.0 Dried Beans and Peas (cooked) Blackeyed peas 1/2 cup 4.1 0.5 3.6 Garbonza beans 1/2 cup 4.0 1.2 2.8 Kidney beans 1/2 cup 8.2 3.6 4.6 Lentils 1/2 cup 4.5 0.7 3.8 Pinto beans 1/2 cup 10.3 3.9 6.4 Split peas 1/2 cup 3.4 1.1 2.4 Breads/Rice/Pasta Pumpernickel bread 1 slice 2.3 1.0 1.3 Rye bread 1 slice 1.6 0.7 0.9 Sourdough bread 1 slice 0.7 0.2 0.5 White bread 1 slice 0.6 0.3 0.3 Whole wheat bread 1 slice 2.2 0.5 1.7 Brown rice 1/2 cup 1.8 0.2 1.6 White rice 1/2 cup 0.6 0.2 0.4 Wild rice 1/2 cup 1.3 0.2 1.1 Spiral pasta, cooked 1 cup 1.3 0.2 1.1 Spiral pasta, whole wheat. cooked 1 cup 3.7 0.7 3.0 Nuts and Seeds Almonds 1/4 cup 3.9 0.4 3.5 Cashews 1/4 cup 1.1 0.6 0.5 Peanuts,dry roasted 1/4 cup 2.5 0.7 1.8 Walnuts 1/4 cup 1.4 0.5 0.9 Sesame seeds 1/4 cup 3.3 0.7 2.6 Sunflower seeds 1/4 cup 2.2 0.7 1.5 Breakfast Cereal All-Bran with Extra Fiber 1/2 cup 15.0 1.0 14.0 Bran Buds 1/3 cup 10.7 2.8 7.9 Cherrios 1 cup 1.6 1.0 0.6 Corn Flakes 1 cup 0.7 0.4 0.3 Fiber One 1/2 cup 13.0 1.0 12.0 Oatmeal, cooked 1 cup 4.0 2.4 1.6 Shredded Wheat, small biscuits 1 cup 4.2 0.7 3.5 Total Raisin Bran 1 cup 6.0 0.9 5.1 Some of this information from THE NUTRITION BIBLE, Jean Anderson and Barbara Deskins. Copyright © 1995 by Jean Anderson and Barbara Deskins.
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