Nutrition is the process of consuming, absorbing, and using nutrients needed by the body for growth, development, and the maintenance of life; nutrients are chemical substances in foods that nourish the body.
Many nutrients can be synthesized in the body'. Those that cannot be synthesized in the body called essential nutrients-must be consumed in the diet. They include amino acids (in proteins), certain fatty acids (in fats and oils), minerals, and vitamins. Nine of the 20 amino acids in proteins are essential nutrients. If essential nutrients are not supplied in the quantities required, nutritional deficiency disorders may result. To determine whether a person is getting enough nutrients, a doctor asks about eating habits and diet, performs a physical examination to assess the composition (the amount of fat and muscle) and functioning of the body, and orders laboratory tests to measure the nutrient content of blood and tissues.
Generally, nutrients are divided into two classes: macronutrients and micronutrients. Macronutrients, which include proteins, fats, carbohydrates, and some minerals, are required daily in large quantities. They constitute the bulk of the diet and supply the energy and building blocks needed for growth, maintenance, and activity. Micronutrients are required in small quantities milligrams (one thousandth of a gram) to micrograms (one millionth of a gram). They include vitamins and trace minerals that catalyze the utilization of macronutrients. Other useful components of food aren't digested or metabolized to any appreciable extent. These components include some fibers, such as cellulose, pectin, and gums. Authorities recommend that 20 grams of fiber be consumed daily to improve movement in the gastrointestinal tract, moderate the changes in blood sugar and cholesterol that occur after meals, and increase the elimination of cancer-causing substances produced by the bacteria in the large intestine. Food additives such as preservatives,...
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