Diet is the food and drink that a person takes regularly day after day. The word diet also refers to the amounts or kinds of food needed under special circumstances, such as losing or gaining weight. Diet needs vary according to age, weight, health, climate, and amount of activity. Dietetics is the science of feeding individuals or groups. The money that is available and health and nutritional needs affect the type of feeding prescribed.
Normal diet,
or balanced diet, contains all the food elements needed to keep healthy. A person needs minerals, proteins, vitamins, and certain fats to build and maintain tissues and to regulate body functions. Proteins, fats, and carbohydrates are used to provide energy and heat. Food elements often eaten in smaller than recommended amounts include calcium, iron, and vitamins A, C, and D, and folic acid (a B vitamin also called folate). A diet that lacks any needed food element may cause certain deficiency diseases. For example, lack of vitamin C causes scurvy, and lack of iron, folic acid, or vitamin B12 may cause anemia.
Diets for losing or gaining weight.
Both the energy value of food and the energy spent in daily activity are measured in units of heat called kilocalories. These units are usually referred to simply as calories. Diets for gaining or losing weight are based on the amount of calories taken into the body in food and the amount of calories used up in activity. If people take in more calories than they use up, they will gain weight. They will lose weight if they take in fewer calories than they use up. A diet aimed toward losing or gaining weight should include all necessary food elements. People should seek the advice of a doctor before beginning such a diet.
Special diets
may be prescribed for people with certain conditions. For example, a person with diabetes must limit use of sugar. Doctors may prescribe low-salt diets for patients with certain heart or kidney diseases.
Some people have allergic reactions to certain foods, such as milk, strawberries, wheat, eggs, or nuts. These people should avoid such foods and consult a physician.
Certain groups of people, such as young children or older people, have special dietary needs. Because children grow rapidly, they need food not only to replace worn-out tissues and provide energy, but also to build new tissue. Older people need the same variety of nutrients as children and young adults. But if their activity is reduced, they need fewer calories. Expectant or nursing mothers and babies also need special diets.
