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Why Does the Human Body Not Digest Corn?

by
author image Dr. Tina M. St. John
Tina M. St. John runs a health communications and consulting firm. She is also an author and editor, and was formerly a senior medical officer with the U.S. Centers for Disease Control and Prevention. St. John holds an M.D. from Emory University School of Medicine.
Why Does the Human Body Not Digest Corn?
Open ears of yellow corn. Photo Credit Maksym Narodenko/iStock/Getty Images

It probably happened when you were just a kid -- the first time you noticed that corn looks remarkably similar passing from your body as it did going in. Although it appears that corn passes through your gastrointestinal system undigested, most of the internal nutrients are broken down and absorbed into your bloodstream. The fibrous outer shells of corn kernels, however, do not break down due to lack of the necessary digestive enzymes.

Parts of Corn Kernels

Corn kernels are the seeds of the plant. The tough outer covering of the kernel is the pericarp, or bran coat. This portion of the kernel remains largely intact in your digestive tract. Inside the bran coat are the germ and the endosperm. The germ is the would-be plant portion at the base of the kernel. The endosperm, which makes up the majority of the kernel, provides nourishment to the germ. Corn is a classified as a starchy vegetable because the endosperm is roughly 85 to 90 percent starch, reports agricultural scientist Vijay Singh, Ph.D., of the University of Illinois Urbana-Champagne.

How Bran Coat Resists Digestion

The plant fiber cellulose is the primary constituent of the bran coat of corn kernels. Like starch, cellulose consists of individual sugar molecules chemically linked together. But the way in which sugar molecules in starch and cellulose bind together differs. Your digestive system produces enzymes that quickly and easily break down the chemical bonds in starch, releasing sugar molecules that pass into your bloodstream. These digestive enzymes, however, cannot break the chemical bonds between the sugar molecules in cellulose. Therefore, the bran coat of corn kernels passes through your intestines intact.

Indigestible, but Beneficial

Although corn's bran coat passes through your gastrointestinal tract without breaking down, this dietary fiber provides health-related benefits. The cellulose in corn bran absorbs water, which keeps your stool soft and promotes regular bowel movements. Additionally, the bulkiness of water-soaked cellulose causes you to feel full for an extended period of time, which may help with weight control.

Digestible Nutrients in Corn

Corn contains protein, sugar, starch and fat, all of which are digested in your gastrointestinal tract and absorbed into your bloodstream. A cup of cooked fresh, frozen or canned corn provides you with 4 to 5 grams of protein; 1 to 2 grams of fat; 5 to 7 grams of sugar; and 25 to 26 grams of starch. These digested and absorbed nutrients from a cup of corn supply you with roughly 140 calories of energy.

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