Digestion Of Carbohydrates
Carbohydrates are the major source of energy for running the body’s various chemical processes. This energy, stored in the chemical bonds of carbohydrate molecules, drives everything from metabolism to movement, enzyme activity, excretion, and growth. Carbohydrates are a large and diverse group of molecules composed chiefly of carbon, oxygen, and hydrogen. In addition to providing metabolic energy to the body, carbohydrates also form structural units. Deoxyribose, for example, is a sugar that makes up the backbone of DNA. The body can also convert carbohydrates into other compounds, such as fat (which is how calories from a candy bar find their way to our waistlines). Finally, carbohydrates can be converted into some amino acids to replenish proteins degraded by other metabolic processes.
Carbohydrates can be divided into three major groups: monosaccharides (single-sugar molecules), disaccharides (a short chain of two sugar molecules), and polysaccharides (a chain of three or more sugar molecules). Monosaccharides and disaccharides are simple sugars. These include glucose, fructose (e.g., honey), and sucrose (table sugar). Reading any packaged food label will instantly reveal how common these items are in our everyday diet. Most mono and disaccharides are sweet, and hence large quantities are used in making desserts, sodas and candies.
Polysaccharides are the most complex type of carbohydrate. They are composed of long strings of monosaccharides, which can form either straight or branched structures. Polysaccharides usually lack the sweetness of the simpler sugars and many are not soluble in water. Vegetables, grains, and wholegrain breads contain an abundance of polysaccharides. Examples of polysaccharides include glycogen, starch, and cellulose. Glycogen is a string of glucose that is made and stored in the muscles and liver, and used as an energy reserve. Starch is a major source of dietary carbohydrates (pasta, bread, and potatoes all contain an abundance of starch) and is digested in the mouth and intestine by the amylase enzymes. Starch is a plant product that is used by plants as an energy reserve, similar to the way glycogen is used by animals. When broken down by digestive enzymes, it is converted to glucose, which is why you may notice a sweet taste in your mouth after eating crackers orwhite bread. Because of its quick conversion to glucose, starch is used as a ready source of energy by animals. Cellulose is also a product of plants. It is the major structural element of a plant’s cell wall and is not digestible by humans. Cellulose is a major component of dietary fiber; it is thus often used as an ingredient in non-chemical laxative products.