Carbohydrates are the most widely distributed and abundant organic compound on earth. They  play an important role in the metabolism of animals and plant. Carbohydrate biosynthesis in plants starting from carbon dioxide and water with the help of light energy (Photosynthesis) is the basis for the existence of all other organisms which depend on the intake of organic substances with food.

Functions: They are the major source of biological energy through their oxidation in the tissues.They also furnish organic precursors for the biosynthesis of many cell components.

Sources: Carbohydrate rich foods are abundant and cheap compared with fats and protein. Food carbohydrates are starches and sugars found in cereal grains, tubers, vegetables, legumes, fruits, milk and milk products. Fructose is present in honey. Fiber, consisting largely of cellulose and other non digestible cell-wall polymers of plant origin plays no metabolic role but helps to maintain proper motility in the intestinal tract.