nutrition

Strategy adopted by an organism to obtain the chemicals it needs to live, grow, and reproduce. These chemicals are nutrients that are absorbed from the environment, such as mineral salts, or chemicals made inside the body of a plant or animal. Nutrition is a term also used to describe the science of food, and its effect on human and animal life, health, and disease. Nutrition involves the study of the basic nutrients required to sustain life, their bioavailability in foods and overall diet, and the effects upon them of cooking and storage. It is also concerned with dietary deficiency diseases.

Plant nutrition is very different from animal nutrition in several ways. In a plant high-energy food (for example, carbohydrate) is made inside the plant by photosynthesis. An animal obtains high-energy food by eating a plant or another animal. Nutrients from the environment are absorbed by different parts of plant and animal bodies. In a plant, nutrients are absorbed from soil water by the roots (see root hair cell). In an animal, nutrients are absorbed from the gut by the epithelium cells lining it.

There are six classes of nutrients: water, carbohydrates, proteins, fats, vitamins, and minerals.

Water Water is involved in nearly every body process. Animals and humans will succumb to water deprivation sooner than to starvation.

Carbohydrates Carbohydrates are composed of carbon, hydrogen, and oxygen. The major groups are starches, sugars, and cellulose and related material (or ‘roughage’). The prime function of the carbohydrates is to provide energy for the body; they also serve as efficient sources of glucose, which the body requires for brain functioning, utilization of foods, and maintenance of body temperature. Roughage includes the stiff structural materials of vegetables, fruits, and cereal products.

Proteins Proteins are made up of smaller units, amino acids. The primary function of dietary protein is to provide the amino acids required for growth and maintenance of body tissues. Both vegetable and animal foods are protein sources.

Fats Fats serve as concentrated sources of energy, and protect vital organs such as the kidneys and skeleton. Saturated fats derive primarily from animal sources, unsaturated fats from vegetable sources such as nuts and seeds.

Vitamins Vitamins are essential for normal growth, and are either fat-soluble or water-soluble. Fat-soluble vitamins include A, essential to the maintenance of mucous membranes, particularly the conjunctiva of the eyes; D, important to the absorption of calcium; E, an anti-oxidant; and K, which aids blood clotting. Water-soluble vitamins are the B complex, essential to metabolic reactions, and C, for maintaining connective tissue.

Minerals Minerals are vital to normal development; calcium and iron are particularly important as they are required in relatively large amounts. Minerals required by the body in trace amounts include chromium, copper, fluoride, iodine, iron, magnesium, manganese, molybdenum, phosphorus, potassium, selenium, sodium, and zinc.

Recommended daily allowances (RDAs) have been established for these nutrients to give a balanced diet.