Corn is a widely consumed food, yet a common observation is that corn kernels often appear undigested in stool. This phenomenon might lead some to believe that corn provides no nutritional value, but this is a misconception. The visible kernels are primarily the outer protective layers, while the inner, nutritious components are largely digested. This article explores the scientific reasons why humans cannot fully process corn and what parts of it do get broken down and absorbed.
The Indigestible Barrier
The primary reason corn kernels often pass through the digestive system seemingly intact lies in their outer layer, known as the pericarp or hull. This tough outer covering serves as a protective barrier for the inner parts of the kernel, shielding them from damage, desiccation, and disease. The pericarp is largely composed of cellulose, a type of insoluble dietary fiber. Cellulose is a complex carbohydrate that forms the cell walls of plants, providing them with structural rigidity. In common corn, the pericarp constitutes approximately 5-6% of the kernel’s dry mass and contains about 23% cellulose, alongside hemicellulose and other components.
The Enzyme Factor
Humans lack the specific digestive enzyme, cellulase, which is necessary to break down cellulose. The human digestive system is equipped with enzymes like amylase and lipase that break down starches and fats, but it does not produce cellulase. Without this enzyme, the robust structure of cellulose remains largely unaffected by human digestive processes. This contrasts with herbivores, such as cows, that either produce cellulase or host microorganisms in their digestive tracts that do, enabling them to effectively digest cellulose.
Beyond the Kernel: What We Do Digest
Despite the indigestible pericarp, humans derive significant nutritional value from corn. The inner parts of the corn kernel, primarily the endosperm and the germ, are readily digestible. The endosperm constitutes about 82% of the kernel’s dry weight and is a rich source of carbohydrates, mainly starch, which is easily broken down into glucose for energy. The germ, the living part of the kernel, contains essential genetic information, enzymes, vitamins, and minerals. It is also rich in lipids, proteins, B vitamins, and minerals like iron and zinc.
Maximizing Digestion
Although the pericarp is resistant to digestion, certain methods can help make the inner nutrients of corn more accessible. Thorough chewing is an important first step, as it physically breaks down the tough outer layer, allowing digestive enzymes to reach the starches and other components within. Cooking methods, such as boiling or steaming corn, can also soften the pericarp, further aiding in its physical disruption. Additionally, processing corn into products like cornmeal or tortillas, through methods like grinding or nixtamalization, significantly disrupts the pericarp. This physical breakdown increases the surface area, making the internal starches, proteins, and fats more available for enzymatic digestion and nutrient absorption.