Insulin and human obesity.
The prevalence of obesity among modern communities increases dramatically and trends to achieve the characteristics of an epidemic. Obesity is the result of a sedentary life style and increased food intake, which characterises western communities. Obesity is closely related to insulin resistance and hyperinsulinemia and the very frequent combination of obesity and NIDDM is characterised as "Diabesity". The behaviour of man in seeking food and the amount of food consumption is a complicated situation, which is regulated by the CNS and especially in the arcuate nucleus of the hypothalamus. A repertoire of neurohormonal actions, generated in peripheral tissues and integrated in the CNS, encompasses many peptides with orexigenic and anorexigenic actions. Two main hormones, insulin and leptin, accomplish the fine-tuning of these peptides action at the critical level of body weight and energy control. The high prevalence of insulin resistance and hyperinsulinemia in obesity indicates a causative relationship between these two situations. It seems likely that insulin resistance in muscle cells is the prime "defect" which renders individuals vulnerable to obesity. The high prevalence of insulin resistance, about 25%, among otherwise healthy subjects indicates that this genetically determined "defect" may be the result of an evolutionary selection which rendered mankind capable of surviving during long periods of famine, in his long journey from the hunter-gatherer period of his life to the present time of plenty.