Your body requires water, vitamins, minerals, protein, carbohydrates and fats for nourishment. You must break down, or digest, some of these nutrients into smaller components for absorption to occur. You digest nutrients by physical and chemical means. Physically, the teeth and oral cavity work to mechanically break down your food into smaller pieces. The chemical breakdown of nutrients occurs through enzymes that are present throughout your digestive tract.
Types
The carbohydrate is generally the most abundant nutrient in your diet. Carbs come from a variety of sources that include everything from simple sugars to complex carbs, which include glycogen, cellulose and starch. Glycogen is the major storage form of glucose in your body, while cellulose is the principal component of plant cell walls and is resistant to human digestive enzymes. Starch in your diet comes in two forms, either amylose or amylopectin, which differ in how the chains of glucose are linked together.
Digestion
Carb digestion begins in your mouth with the chewing and secretion of salivary enzymes. Although some digestion occurs in the mouth and stomach, most carbohydrate digestion occurs within your small intestine, which releases an enzyme, known as alpha amylase, which breaks down the amylose and amylopectin in food into the simpler carb forms glucose, maltose and isomaltose. While glucose is already a monosaccharide, maltose and isomaltose are disaccharides. Your body can only absorb monosaccharides through the intestine, so the remaining disaccharides are broken down into glucose by other digestive enzymes, known as glycosidases, at the point of intestinal absorption.
Dietary Fats
Lipids, or fats, in your diet include phospholipids, sterols and triglycerides. The primary components of dietary fat are triglycerides, which are generally composed of a single glycerol molecule and three fatty acid molecules. Your body must break down the triglyceride into two fatty acid molecules for absorption to occur.
Digestion of Fats
Fat digestion, like carbohydrate digestion, begins in your mouth. You secrete enzymes, known as lipases, in your mouth, stomach and small intestine that work to digest dietary triglycerides. Although you have lipases working in the mouth and stomach, the vast majority of triglyceride digestion occurs within the small intestine. Digestion of triglycerides, and other lipids, is a long process. For you to completely digest and absorb dietary fat, your body will require up to 24 hours for this process.
References
- "Journal of Nutrition"; "Starch Digestion and Absorption in Nonruminants"; G.M. Gray; January 1992.
- "Annals of Nutrition and Metabolism"; "Fat and Fatty Acid Terminology, Methods of Analysis and Fat Digestion and Metabolism: A Background Review Paper"; W.M. Ratnayake; September 2009
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