What Is Fiber?

Fiber is a carbohydrate that can’t be digested by the human body. It is found in plants we eat such as fruits, vegetables, whole grains, beans, nuts, and seeds. Unlike most nutrients, it is not absorbed by our bodies but passes through the digestive tract largely intact. Yet fiber is very important to good digestive health and also protects against several serious diseases.

There are three types of dietary fiber:

Soluble fiber dissolves in water and turns into a type of gel during digestion. This slows the process of digestion and nutrient absorption. Good sources of soluble fiber include:

  • Oat bran
  • Oatmeal
  • Nuts and seeds
  • Legumes (dried peas, beans, lentils)
  • Apples, pears, and citrus fruits
  • Vegetables such as potatoes and Brussels sprouts

Insoluble fiber does not dissolve in water. Instead, it absorbs many times its weight in water. This creates a soft bulk and appears to speed up the passage of foods through the stomach and intestines. It also adds bulk to the stool. Good sources of insoluble fiber include:

  • Wheat, corn and rice bran
  • Brown rice
  • Whole-grain cereals and breads
  • Dried beans and peas
  • Nuts and seeds

Resistant starch is the part of starchy foods (approximately 10 percent) which is tightly bound by fiber and resists normal digestion. Friendly bacteria in the large bowel ferment and change the resistant starch into short-chain fatty acids which are important to bowel health and may protect against colon cancer. Examples of starchy foods include:

  • Bread
  • Cereals
  • Rice
  • Pasta
  • Potatoes
  • Legumes