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Fiber Facts: What Is Fiber Anyway?

Learn about the different types of fiber found in food.

Fiber Facts: What Is Fiber Anyway?

Fiber is a mix of many different substances found in plant cell walls and is not digestible by the human body. In it comes and out it goes. How can a substance we cannot even digest (and, by the way, has no nutritional value) be so beneficial? Might sound crazy, but once inside your body, fiber does some pretty amazing things. The term dietary fiber, when listed on a nutritional label, simply refers to the amount of these indigestible substances in a specific food product. This way, you can identify a food rich in fiber.

Fiber fits in two categories, insoluble and soluble, depending upon its ability to dissolve (or not dissolve) in water. Some foods contain both soluble and insoluble fiber, whereas others are predominant in only one. The key is to eat a variety of fiber-rich foods each day and receive the beneficial effects from both types.

Soluble Fiber

Water-soluble fiber readily dissolves in water. Technically speaking, soluble fibers include pectins, gums, and mucilages. It's obvious, however, that these terms won't be of any help to you in your grocery store. Translated into “real-food” terminology, you'll find soluble fiber in the following:

  • Oats
  • Brown rice
  • Barley
  • Oat bran
  • Dried beans and peas
  • Rye
  • Seeds
  • Vegetables (especially carrots, corn, cauliflower, and sweet potatoes)
  • Fruits (especially apples, strawberries, oranges, bananas, nectarines, and pears)

Why all the hoopla? Well for starters, foods rich in soluble fiber have been shown to help decrease blood cholesterol, therefore reducing the risk of heart disease. Another benefit comes from its ability to slow the absorption of glucose (sugar in the blood), which might in turn help control blood-sugar levels in diabetics.

Insoluble Fiber

The type of fiber that does not readily dissolve in water is called water-insoluble. Insoluble fiber includes lignin, cellulose, and hemicellulose. Once again, converted into understandable food terms, we are talking about the following:


Diverticulosis is an illness or condition where tiny pouches (called diverticula) form in the wall of the colon. The condition is often without symptoms, but when the pouches become infected or inflamed, it can be painful. When this happens, the condition is known as diverticulitus, which can cause fever, abdominal pain, and diarrhea.

  • Wheat bran
  • Corn bran
  • Whole-wheat breads and cereals
  • Fruits
  • Vegetables (especially potatoes with skin, parsnips, green beans, and broccoli)

As you can see, some foods are mentioned on both lists, indicating that they provide both soluble and insoluble fiber.

Insoluble fiber is primarily responsible for accelerating intestinal transit time, along with increasing and softening stools. In other words, insoluble fiber is responsible for “moving things along.” In addition to promoting regularity, insoluble fiber has been shown to decrease your risk for hemorrhoids and diverticulosis.


Just because a food sounds healthy doesn't necessarily mean that it is. Some bran muffins are loaded with fat and sugar—certainly not worth the small amount of fiber they provide.

Lowering Your Cholesterol Level

If your cholesterol tends to be a bit high, or you'd just like to maintain an already low number, you might want to increase your soluble fiber. Soluble fibers have been shown to bind with cholesterol and pull it out of the body. Fruits, vegetables, legumes, oats, and all foods made with oat bran can therefore reduce your risk for heart and artery disease by lowering blood cholesterol. Another thought is that high-fiber foods can displace some of the high-fat, artery-clogging foods in your diet—a double impact!

Feeling Fuller with Less Food

Did you ever feel as though a plate of vegetables expanded in your stomach after you ate it? Well, it did! Eating fiber-rich foods can make you feel full because they absorb water and swell inside you. You might also feel full longer if you choose a meal with some soluble fiber. Unlike insoluble fiber, which quickly moves food through your body, soluble fiber tends to stick around a while, keeping you full and satisfied.

Does this mean you'll lose weight from eating a lot of fiber? It does if you eat these foods instead of the high-fat, high-calorie stuff. If you eat them in addition to all the junky food, your chance of becoming slim is slim.

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