The physiological function of nutrients In foods may be divided into three general categories: the need for food to supply energy, the need for food to build and maintain the body tissues, and the need for food materials to regulate body processes.
These needs are satisfied by substances called nutrients which are found in the food. The foods we consume daily include, rice, wheat, pulses, vegetables, fruits, milk, eggs, fish, meat, sugar, butter, and oils.
These foods are made up of one or more of a number of substances called nutrients which are classified into six groups according to their chemical composition. So we discuss about nutrients in foods in this article.
1. Carbohydrates are main nutrients In foods
These constitute one of the three major classes of nutrients (carbohydrates, fats and proteins) which supply energy. Each gram of carbohydrate consumed provides 4 kilocalories of energy to the body.
Carbohydrates are formed in plants from carbon dioxide and water by photosynthesis in sunlight. So the solar energy is stored as it in chemical energy in the form of carbohydrates (starch, sugar) in the plant.
Carbohydrates contain the elements carbon, hydrogen and oxygen. Starch is present mainly in cereals, pulses, roots and tubers. Sugar is found in fruits, sugarcane and sugar beet.
Carbohydrates which provide a major portion of calories in the human diet are of two kinds: complex carbohydrates like starch and simple sugars like monosaccharides (glucose, fructose) and disaccharides (sucrose).
Apart from serving as a source of energy, the intermediary products of carbohydrate metabolism provide substrates for synthesis of a wide range of biocompounds in the body.
Diabetes is a disease of impaired carbohydrate metabolism manifest as hyperglycemia.
2. Fats and Oils
These are esters of glycerol and fatty acids and form the second group of major nutrients. They contain carbon, hydrogen and oxygen, but the proportion of oxygen present is much smaller than in carbohy drates.
Each gram of oil or fat supplies 9 kilocalories of energy. Thus these are a more concentrated source of energy than carbohydrates. Oils and fats are obtained from the plants and animals.
Dietary fat is essential, as a source of essential fatty acids (EFA), as a vehicle for fat soluble vitamins and for providing a certain level of energy density and palatability to diets.
Besides cardiovascular diseases, high fat intake is also a risk factor in obesity and diabetes. High fat intakes particu larly of the saturated type have been shown to be associated with occurrence of cancer at several sites, especially the breast, prostate and large bowel.
Experimental evidence indicates that polyunsaturated fats are tumorigenic. All the nutrients the causal relationship between fat intake and occurrence of cancer is most suggestive.
3. Proteins are main nutrients In foods
This is the third class of major nutrients. There are thousands of proteins found in nature which vary in their composition and size. All the proteins contain the elements carbon, hydrogen, oxygen and nitrogen.
Proteins are made up of smaller units known as amino acids. Each gram of protein supplies 4 kilocalories of energy.
Proteins are essential for tissue building and maintaining equilibrium. Protein in the diet should be derived from different sources and provide at least 10 to 12 per cent energy, and such levels would meet the normal protein requirements of all age groups.
The term mineral refers to inorganic substances present in foods. They include salts and other compounds of calcium, phosphorus, magne sium, sodium, chlorine, potassium, sulphur and other elements. On heating to high temperature (about 550°C) they are converted to ash.
Body needs a wide range of macrominerals (K, Na, Cl, Mg, Ca, P) and trace elements (Cr, Co, Cu, F, I, Fe, Mn, Mo, Ni, Se, Si, Sn, V and Zn)
for maintaining body function and health at an optimum level. Quantitative requirements for man of several of these elements have been defined.
5. Vitamins are main nutrients In foods
These are organic compounds present in very small amounts in foods, but essential for normal growth of the body and maintenance of health.
Vitamins may be fat-soluble such as A,D, E or K or water-soluble such as vitamin C (ascorbic acid), thiamine, riboflavin, niacin and others which belong to the B-complex group.
Water is an essential part of the body structure as a carrier of nutrients and regulator of a number of body functions. Its importance as a nutrient has been recognized only recently.
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