• Carbohydrates – The Carbohydrate are compounds made of sugars. These are classified by their number of sugar units; such as - monosaccharides (such as glucose and fructose), disaccharides (such as sucrose and lactose), oligosaccharides, and polysaccharides (such as starch, glycogen, and cellulose).
• Proteins – The proteins are organic compounds which consist of the amino acids joined by peptide bonds. The body cannot manufacture some of the amino acids; these are termed essential amino acids; the food that we take must supply these. In nutrition, proteins are broken down through digestion by proteases back into free amino acids.
• Fats- The fats consist of a glycerin molecule with three fatty acids attached. Fatty acids are unbranched hydrocarbon chains, connected by single bonds alone i.e. saturated fatty acids or by both double and single bonds i.e. unsaturated fatty acids. Fats are needed to keep cell membranes functioning properly, to insulate body organs against shock, to keep body temperature stable, and to maintain healthy skin and hair. The body does not manufacture certain fatty acids; these are termed as essential fatty acids and our diet must supply these.
• Fat has an energy content of 9 kcal/g (~37.7 kJ/g); proteins and carbohydrates 4 kcal/g (~16.7 kJ/g). Ethanol (grain alcohol) has an energy content of 7 kcal/g (~29.3 kJ/g)
Substances which support metabolism
• Dietary minerals – These are generally trace elements, salts, or ions such as copper and iron. Some of these minerals are essential to human metabolism.
• Vitamins – These are organic compounds essential to the body. They usually act as coenzymes or cofactors for various proteins in the body.
• Water – The Water is an essential nutrient and is the solvent in which all the chemical reactions of life take place.