Becky Harrison, age 15, of Watertown, N.Y., for her question:
WHAT IS BASAL METABOLISM?
Metabolism is the process by which all living things, including humans, animals and plants, transform food into energy and living tissue. The rate of metabolism depends on various factors including the amount of food eaten, temperature and activity.
Metabolism settles down to a minimum constant rate when a person is at rest in a room with comfortable temperature several hours after a meal. Doctors call this rate the "basal" metabolism.
Normal persons of the same body size, age and sex have much the same basal metabolic rate, or rate at which the tissues burn food. The rate may be expressed as a plus or minus percentage of the normal rate.
The basil metabolism provides a standard to compare metabolism under the varying conditions of health and disease.
The thyroid hormone, which is secreted into the blood stream by the thyroid gland, performs most of the regulation of the rate of metabolism. By measuring the basil metabolic rate, doctors can determine whether or not the thyroid is operating properly.
A low rate indicates hypothyroidism, or too little thyroid hormone. A high rate indicates hyperthyroidism, or too much thyroid hormone.
To measure basal metabolism, doctors usually use a blood test called the protein bound iodine (PBI) test. The PBI test measures the amount of iodine connected to protein molecules in a blood sample.
In only a few cases, abnormal thyroid hormone levels do not indicate an abnormal metabolic rate. In these cases, doctors use an instrument called a metabolimeter to measure basal metabolism.
A metabolimeter measures the amount of oxygen a person uses while resting. The amount of oxygen used indicates how quickly the body is using up food and producing energy.
Metabolism can be thought of as the sum of two related chemical processes that take place inside the body. These actions are called "catabolism" and "anabolism."
Catabolism, or destructive metabolism, is the breaking down of food substances to release energy and digest food. Anabolism, or constructive metabolism, is the synthesis or building up of cells and tissues, and the repair of worn out tissues.
Energy released during catabolism is used in three ways: to make the reactions of anabolism work, to heat the body and to enable the body's muscles and nerves to do their work.
Materials used in the process of metabolism are formed during digestion and put to work through respiration in the cells.
After food enters the body, it is broken down in the digestive tract. Enzymes in the digestive tract split the complex molecules of proteins, fats and carbohydrates into smaller chemical units. These smaller units, or food fuels, pass through the walls of the intestines into the blood stream