Carbohydrates

Carbohydrates are the main source of energy in a common man's diet. Carbohydrates are made up of carbon, hydrogen and oxygen (hence the name : carbo + hydrates). Each gram of carbohydrate provides approximately 4 Calories in diet (except cellulose, which doesn't give us any energy).

Carbohydrates are of the following types:

Starch

Starch is basic to human diet. It is the most important of all carbohydrates. It is found in abundance in cereals, roots and tubers. A good example of starch is potato. Chemically, starch contains numerous sugar molecules joined together in chains and sheets.

Starch is stored in human body in the form of glycogen. An average human contains about 500 grams of glycogen in his body. Most of it is concentrated in liver and muscles. This reserve is rapidly exhausted on fasting. It is estimated that all glycogen is depleted from the body within 48 hours of fasting. Once the glycogen reserve is depleted, the body starts breaking up protein and stored fat for energy.

Sugars

Sugars are usually sweet in taste. Some sugars may have a bitter aftertaste too. Sugars can be monosaccharides (like glucose, fructose and galactose) or disaccharides (sucrose, lactose and maltose). These monosaccharide and disaccharide sugars are highly soluble in water, and are therefore, easily assimilated. Because they dissolve readily in water, sugar solutions have traditionally been used as a quick source of energy.

Cellulose

Cellulose is largely indigestible in human beings. Herbivores like cow, buffalo, gazelle etc. can obtain energy from cellulose because they have enzymes that digest cellulose into smaller sugars. But we humans lack the enzymes required to digest the cellulose. Therefore, cellulose doesn't give us any energy. It forms dietary fibers which are very important in the protection of health.

Cellulose is present abundantly in fresh fruits, vegetables, salads, cereals, and almost any plant product for that matter. Paper is made up of cellulose fibers. Wood contains cellulose in abundance. Wheat husk abounds in cellulose. Now you have a fair idea what ellulose is.