What Makes Fibrous Carbohydrates Hard To Digest?

Fiber-rich carbohydrates are important parts of a nutritious eating plan, but they are more or less resistant to human digestion. You may wonder why public health authorities recommend you eat so much of something your body can't digest. Fiber's benefits include providing you with a sense of fullness and promoting bowel regularity. In addition, according to the Dietary Guidelines for Americans, dietary fiber lowers your risk of cardiovascular disease, obesity and type 2 diabetes. Your body doesn't have the ability to break down many fibrous carbohydrates. As a consequence, much of the fiber you eat enters your colon pretty much intact.

Types and Sources of Indigestible Fiber

By its definition, dietary fiber refers to the component in foods that cannot be digested. There are several types of indigestible fiber, including cellulose, pectin, inulin and gums. Common sources of dietary fiber are fruits, vegetables, nuts and grains. Processing and refining grains generally reduces the fiber content of foods. There's also a substance called lignin that is considered dietary fiber but is not a carbohydrate. It's a compound found in the cell walls of certain plants and seeds, including flaxseed, cashews and sunflower seeds.

Fiber Composition and Human Digestion

Fiber, like all carbohydrates, is made up of linked chains of sugar molecules. However, there are structural connections between these molecules called glycosidic bonds. Humans lack the digestive enzyme necessary to break them down, particularly a type called beta-glycosidic bonds. Cows, horses and other ruminating animals, on the other hand, have bacteria that produce a substance that can break down the cellulose form of fiber. For them, that's mostly grass and hay -- but you eat cellulose, too. It's in foods like celery sticks and alfalfa.

Benefits of Eating Indigestible Fiber

Indigestible fiber aids in the work of the intestinal tract. According to the Linus Pauling Institute at Oregon State University, high-fiber diets can prevent or cure constipation by increasing the size of stools and helping them move more smoothly through the intestines. Moreover, fiber helps keep the colon healthy by discouraging the growth of harmful bacteria and encouraging healthy bacteria. Fiber may have disease prevention benefits as well. For example, AskDrSears.com reports that people who eat high-fiber diets have less incidence of colon cancer, possibly because fiber may shuttle toxins out faster and they may bind to carcinogens, reducing their contact time with the intestinal wall. In addition, fiber can lower after-meal blood sugar response, making it an effective part of a diabetic's eating plan. Fiber also binds with bile acids, which can have a cholesterol-lowering effect.

Fiber Intake Recommendations

Healthy adult men need about 38 g of fiber each day. Women need 25 g daily. After age 50, fiber intake recommendations decrease to 30 g for men and 21 g for women. Some people could have health conditions that require getting more or less fiber. See your health care provider to determine your specific needs.