What’s the difference between soluble and insoluble fiber?

Soluble fiber traps cholesterol molecules and is broken down in the small intestine, while insoluble fiber proceeds almost completely intact through the digestive tract and provides bulk to bowel movements.

Soluble fiber dissolves in water to form a gel that traps cholesterol molecules, and is fermented in the large intestine by bacteria. It can be found in oat bran, the mushy center of a kidney bean, and other soft plant parts.

Soluble fiber represents 75% of all ingested fiber, and is broken down in the intestines, creating gases and short-chain fatty acids. Two of these fatty acids, acetate and propionate, enter the circulation. The other fatty acid, butyrate, acts as an energy source for the colon lining and promotes overall colon health.

Insoluble fiber cannot be completely digested or fermented, and passes through the intestinal tract in the feces. This type provides the roughage often associated with fiber. It can be found in fruit skins, nuts, wheat kernels, and others.

This comprises about 25% of all ingested fiber, and helps to promote regularity of bowel movement.