Fiber is a type of carbohydrate that the body cannot digest. Unlike other carbohydrates, fiber cannot be broken down into sugar molecules, and instead, it passes relatively intact through the digestive system. The National Academy of Medicine defines fiber as dietary fibers (nondigestible carbohydrates and lignans) that occur naturally in plants and functional fibers that are extracted from plants or synthetically made and are nondigestible with a beneficial health effect in humans. Some types of fiber fall into both categories, such as oligosaccharides and resistant starches that may be naturally occurring or synthetically made.
There are two types of fiber: soluble and insoluble. Soluble fibers come from the insides of plants and include substances such as pectin. They are present in fruits, vegetables, oats, and barley and may help manage blood sugar and cholesterol levels. Insoluble fibers come from the outer skins of plants and pass straight through the digestive system. They can help prevent constipation.
Dietary fiber can offer several benefits, including preventing constipation, managing blood sugar, and reducing the risk of heart disease, stroke, and some types of cancer. Health authorities recommend that men and women eat 38 and 25 grams of fiber per day, respectively. Good sources of fiber include fruits, vegetables, whole grains, nuts, and seeds.
