The increase in obesity prevalence is problematic as this condition is associated with health complications such as diabetes and cardiovascular diseases, more particularly when the excess body fat is stored in the deep abdominal region. On the other hand, obesity facilitates the maintenance of body homeostasis probably because of an increased hormonal gradient which favours the regulation of energy balance, to give but one example. The regulation potential of excess body fat is particularly apparent in the reduced-obese state where a reduction of energy expenditure, fat oxidation and some immune system markers, as well as an increase in appetite, stress vulnerability and circulating and adipose tissue organochlorines have been observed. These constitute another category of risk factors which can certainly favour the accumulation of body fat to reestablish body homeostasis on other fronts. Under such conditions, obesity is perceived by the physiologist as a necessary biological adaptation rather than a disease. For health professionals, this emphasizes the importance to seek a reasonable compromise between the favourable reduction of risk to develop metabolic complications by body weight loss and the physiological vulnerability which is also generated by such an intervention.