IV. Life Stages
Basal Energy Expenditure
Basal Energy Expenditure (BEE, also called basal metabolic rate, or BMR):
- This is the energy needed to carry out fundamental metabolic functions, such as breathing, ion transport, normal turnover of enzymes and other body components, etc.
- It is measured with the subject in the fasted state, lying quietly in a room of comfortable temperature.
BEE may be expressed in terms of surface area: kJ m-2 hr-1. This allows a fair comparison among infants, adults, the lean, the obese, etc.
BEE varies between the sexes. Lean body mass is a major determinant, and women tend to have more body fat (less lean muscle mass). As a result, their BEE is lower than that of otherwise comparable males.
The basal energy expenditure varies with age.
- The peak is in infancy.
- It declines rapidly through childhood and adolescence.
- It continues to fall slowly with increasing age.
- The decline in old age is due largely to loss of muscle.
- This is not inevitable.
- The cause is inactivity (absolute or relative).
- Weight-bearing exercise will prevent or reverse muscle loss among the elderly.
There can be major nutritional consequences to the decline of the REE in advanced age.
- Decreased caloric requirements may lead to decreased food intake.
- Sufficiently low caloric intake can lead to deficient intake of essential nutrients.