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What Materials Are Not Digested?

The process of digestion breaks food into molecules small enough to enter the bloodstream and serve as nutrients for the body. Some materials are not digested and pass through the digestive tract, or alimentary canal, basically unchanged. The most common material consumed by humans that remains undigested throughout the process is cellulose, the main component of plant cell walls. Because humans cannot digest cellulose, it serves as fiber in the diet, providing health benefits.

  1. How It Works

    • In humans, digestion begins in the mouth as the salivary glands excrete saliva, which contains the enzyme salivary amylase. This enzyme begins the digestive process of reducing food to smaller and smaller molecules by initiating the breakdown of starch before food is swallowed. As food moves through the digestive tract and is mixed with digestive juices from the stomach, intestine, pancreas, and liver, food is broken down into smaller and smaller molecules. Once the body absorbs what can be used for nutrition, the remainder is excreted as waste materials.

    Soluble and Insoluble

    • When a substance is described as soluble, it means it is able to be dissolved in another substance. Soluble fibers are those that can be hydrolyzed, i.e., broken down through a chemical reaction with water. Contrastingly, insoluble is used to refer to substances that cannot be dissolved in a liquid. Materials, such as insoluble fibers that cannot be digested by humans move through the digestive tract adding bulk to waste material, which stimulates the intestines to contract and push the material along.

    Sources

    • Soluble fiber, such as that found in fruit, legumes, vegetables and oat bran, dissolves easily after consumption and moves through the digestive tract as a soft gel. Ruminants, or cud-chewing animals, have microorganisms in a special pouch within their digestive system that can break down cellulose into usable nutrients. On the other hand, when humans consume insoluble fiber, such as cellulose, it is virtually unchanged from the time of consumption, until it leaves the body as waste material.

    Benefits

    • Biologists and nutritionists call materials not digested during the process of human consumption dietary fibers. Although dietary fiber has no nutritional value, scientists believe it to be essential to a healthy diet due to other benefits. Undigested materials add bulk to waste products and trigger peristalsis, in this case the contraction of involuntary muscles to transport materials through the intestines, speeding up the process of digestion. This process leads to regular elimination of waste materials from the body, preventing constipation possibly reducing the risk of colon cancer.

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