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basal metabolic rate

Basal metabolic rate (BMR) is the number of calories metabolized at rest during 24 hours and is the key to effective weight management. For a typical patient, BMR accounts for more than ninety percent of total daily expenditure - more than ninety percent of calories are burned while the patient is at rest.

The basal metabolic rate is determined by fat-free mass since only fat-free mass metabolizes. The formula is a simple one - the larger a patient's fat-free mass, the greater the rate of caloric expenditure.

The equation used by the analyzer to predict BMR, based upon Grande and Keys (1), is as follows:

    BMR (calories/day) = 14.15 * Fat-Free Mass (lb)

Converted to metric, the equation is as follows:

    BMR (calories/day) = 31.2 * Fat-Free Mass (kg)

While caloric expenditure is elevated during exercise and occupational activity, the main benefit of exercise is the maintenance of fat-free mass. More fat-free mass means greater caloric consumption all day long, even when the patient is asleep!

Dieting alone may cause a reduction in fat-free mass, and can actually reduce the body's ability to burn calories. The holy grail of weight management is to maintain or increase fat-free mass. This is not always possible during periods of weight loss. So the goal is to minimize reduction of fat-free mass. A typical patient will experience a loss of 0.45 pounds of fat-free mass and 0.55 pounds of fat mass for each pound of weight loss while dieting without maintenance exercise.

1Grande F, Keys A. Body weight, body composition, and calorie status. In R. S. Goodhart and M. E. Shils, eds. Modern nutrition in health and disease, 27, 1980. Philadelphia: Lea & Febiger.
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