Basal Metabolism

Basal Metabolism, the least amount of energy necessary to maintain the vital involuntary activities, including breathing, maintenance of heat, heartbeat and blood circulation, and the activities of the nervous system and internal organs. The basic metabolic rate (BMR) in humans is measured in the so-called basal state: comfortably at rest mentally and physically, awake at normal room temperature, at least 14 hours after eating. Because a definite correlation exists between the production of heat and the consumption of oxygen, the BMR is usually determined by measuring the amount of oxygen consumed in a given length of time. It is expressed as a percentage variation from the average for the person's sex, age, and size; a range of -15 to +15 is considered normal. The BMR is higher in males than in females, is higher in the young and decreases as age advances, is influenced by body size and state of nutrition, and is slightly lower during sleep.

The BMR is an important diagnostic tool, especially in determining disorders of the thyroid gland. Inadequate secretion of the thyroid may lead to greatly depressed metabolism, with mental and physical lethargy; by contrast, oversecretion may greatly stimulate activity and the BMR by as much as 100 percent.