The origins and consequences of obesity. Diabetes

A relationship exists between obesity and non-insulin-dependent diabetes mellitus. Central, abdominal obesity carries a particularly high risk that is most likely associated with enlargement of visceral fat deposits. A multiple endocrine perturbation is associated with visceral obesity. This consists of a hypersensitive hypothalamic-pituitary-adrenal (HPA) axis, with resulting excess of cortisol secretion upon stimulation. Growth hormone levels in both sexes are diminished and testosterone concentrations in men are lower than normal. In women a moderate hyperandrogenism is often present. The elevated sensitivity of the HPA axis may be a primary event, followed by adrenal androgen production in women and by interaction at several levels, with inhibition of both the growth hormone and pituitary-gonadal axes. Together, these endocrine perturbations seem to be able to centralize body fat to visceral depots because of a high density of steroid hormone receptors. The endocrine perturbations are most likely followed by insulin resistance. Elevated cortisol levels, deficiencies in sex-specific steroid hormones and excess androgens result in insulin resistance. The endocrine abnormalities in visceral obesity are followed by insulin resistance, both directly and indirectly via contribution of excess free fatty acids from centralized body fat depots. The hyperactivity of the HPA axis may be due to frequent challenges and it is amplified by a deficient feedback inhibition. A depressive, helplessness reaction to stress may be involved. Such stress factors may be found in socioeconomic and psychosocial handicaps, as suggested by results of population studies. This hypothesis is strongly supported by the reproduction of an identical condition in non-human primates that react with a depressive reaction upon psychosocial types of stressors. The perturbations of the HPA axis may thus be in the centre of the syndrome. Studies of this axis in established non-insulin-dependent diabetes mellitus suggest similar perturbations, but the information is not conclusive.