[kahrâ³bo-hiÂ´drÄt] a compound of carbon, hydrogen, and oxygen, the latter two usually in the proportions of water (CH2O)n. They are classified into mono-, di-, tri-, poly-, and heterosaccharides. Carbohydrates in food are an important and immediate source of energy for the body; 1 g of carbohydrate yields 4 calories. They are present, at least in small quantities, in most foods, but the chief sources are the sugars and starches.