Visceral fat and psychosocial stress in identical twins discordant for obesity

Objectives. Accumulation of intra-abdominal fat has been suggested, but not yet proved, to be basically as a result of chronic psychosocial stress causing arousal of hypothalamic-pituitary-adrena cortex axis. Our objectives were to study the association between psychosocial stress, obesity and body fat distribution when genetic factors are identical. Design. Monozygotic twins discordant for obesity were examined in an in-patient setting. Subjects. Adult monozygotic twin pairs (12 female, 8 male) with an average intrapair difference of 17 kg in body weight. They were divided into two groups: in group A the visceral fat area of the obese cotwin was higher and, in group B, lower than the gender-specific median value. Main measures. Hormonal, physiological and psychological distress indicators, and sleep measures. Results. Daily urinary cortisol and noradrenaline excretion were higher in the obese cotwins when compared with the nonobese cotwins in group A but not in group B (P = 0.026 and 0.020 when intrapair differences were compared between groups A and B, respectively). In serum cortisol, ACTH and CBG concentrations a similar trend was not statistically significant. In group A, the obese cotwins consumed almost 2.5 times as much alcohol as their lean cotwins, whilst in group B the situation was the opposite. The mean amount of active sleep was significantly higher and that of quiet sleep significantly lower in the obese than the lean cotwins only in group A. Intrapair differences in emotional reactions indicating distress and lack of subjective energy were seen only in group A. Conclusion. When genetic factors are identical, visceral fat accumulation, rather than obesity in general, is associated with increased psychosocial stress and concomitant hormonal changes.