set point theory

A theory suggesting that body weight is kept relatively constant by internal control mechanisms similar to those of a thermostat. According to the theory, each adult has a range of body weights that act as a norm or set point; changes in body weight trigger mechanisms to bring the weight back to this set point.

Some researchers believe that the set point is psychological. An individual establishes a perceived set point weight based on personal and cultural preferences. These preferences may be influenced by the person's appearance, body weight measurements, clothing size, health, and so on. Deviations of weight result in changes of physical activity and eating habits that return the weight back to the set point. Other researchers believe that the set point is physiological, but there are a number of different mechanisms proposed. One proposal is that the set point depends on the activity of the hypothalamus, a hormone-secreting gland at the base of the brain; another proposal is that a hormone is secreted by adipose tissue. In either case, it is suggested that deviations of weight result in a physiological corrective mechanism (e.g. change in basal metabolic rate) being switched on. Although dieting does not appear to affect the set point, exercise may lower it, making it easier to lose weight. See also obesity gene.

A theory that postulates that body weight is regulated around a given set point using a homeostatic mechanism similar to that which regulates temperature. Preliminary studies indicate that people who lose weight through semi-starvation or gain weight by overeating return to their normal body weight quickly when they revert to normal eating patterns. It has been suggested that the body has the ability to balance caloric intake and expenditure to within plus or minus 10-15 kcal day⁻¹. It appears that the body attempts to maintain its normal weight when overfeeding or underfed by changing the three components of expenditure (see resting metabolic rate, thermic effect of food, thermic effect of activity). If the set point theory is correct, it explains why some athletes have great difficulty losing or gaining body weight for weight-classification sports, such as wrestling and horse riding.