Temperature & Disease Mechanisms

The regulation of body weight is dependent on a balance between nutrient intake and utilization, although there are other important factors.

Energy is required continuously for cell repair and growth and intermittently for work, although intake of food to provide this energy is intermittent. There is a loss of nutrient energy when food is converted to mechanical energy; about 65% is dissipated as heat. Twelve people sitting talking in a room produce heat at 60 kJ/min, equivalent to a 1 kW electric fire. Total energy expenditure (TEE) has three components:

• Basal metabolic rate (BMR): at complete rest and without physical work (basal metabolism), energy is required for the activity of the internal organs and to maintain body temperature. This is the single largest contributor to TEE, at 6070% of TEE. During sleep, the overall metabolic rate approximates the BMR.
• Thermogenic component: the energy expended through the physiological response following the ingestion of food, and exposure to cold or stimulants.
• Physical activity: only 2535% of nutrient energy is used for mechanical work and less than 10% is for basic physiological activity, e.g. cardiac and respiratory contractions. The energy requirement of an individual is the energy intake that will balance energy expenditure when the individual has a body size, composition, and level of physical activity consistent with long-term good health, and will allow for the maintenance of economically necessary and socially desirable activity. In children and pregnant and lactating women, the energy level includes the energy need associated with the deposition of tissues and the secretion of milk at rates consistent with good health.