Answer
The term homeostasis means a steady or stable state of the internal environment in livings animals. This does not mean that physiolgical parameters like temperature and pH are in variable; what it means is that there is a set point or narrow range of values which the body tries to maintain for optimal health. For instance body temperature and pH of the stomach have well known ranges. Body temperature has a st point of 988.6deg F, and a range of (7.7-99.5 deg F. The ranges of some other physiological parameters are for example: blood has a pH range of 7.35-7.45, and urine has a pH range of 4.6-8.0
Experiments have shown that body weight also has a set point and a narrow homeostatic range that varies from individual to individual.
Experiments have shown that if rats are forced fed so that they become obese; however, when they are allowed to feed voluntarily, they will moderate their food intake so that they return to their normal initial weights. Also if they are starved so that they become underweight, when they are allowed to eat again, they will voluntarily eat enough to regain normal weights. But when normal weights are achieved, they will reduce food intake to maintain and not exceed their normal weights. This indicates that there is a neurological mechanism governing their eating behavior with the goal of keeping body weights within narrow set limits.
Twin studies have shown that humans too have a weight set point , but that this varies from person to person. An inherited point is not the only factor that affects how much a person actually weighs. Behavioral factors that influence body weight significantly are amount of food eaten (intake), amount of physical activity (exercise / physical labor), drugs, viruses etc.
Work Step by Step
Twin studies on humans have shown that weight homeostasis is maintained and can be perturbed by both hereditary, and behavioral factors.
Although living habits seem to have the greater influence on adult body weight; nevertheless, hereditary factors are responsible for about 40% of the effects that determine how much an individual weighs.
