Body fat mass and nutrition influence secretion of the adrenocortical
hormones--
aldosterone and
cortisol--via several mechanisms. However, there are no data on adrenocortical function following widely prescribed mild diet-induced
weight loss (10%) in obese subjects. In the present study, 25 healthy obese volunteers (BMI 32.9+/-4.3 kg/m (2)) followed a 30%
calorie restricted diet over 12 weeks. Hypothalamic-pituitary-adrenal (HPA) axis function was assessed by 24-hour urine free
cortisol/
cortisone and a 1 mcg
ACTH stimulation test with measurement of total and free
cortisol and
corticosteroid-binding globulin (
CBG). The renin-angiotensin-aldosterone system (RAAS) was assessed by measurement of plasma
aldosterone and
renin under
salt depleted (30 mmol/d) and loading (250 mmol/d) conditions. Volunteers' weight fell by 8.5+/-0.8 kg (8.9+/-0.7%) and seated systolic blood pressure fell by 8.7+/-2.7 mmHg and diastolic blood pressure by 7.0+/-1.4 mmHg (p<0.01). Plasma
aldosterone and
renin levels fell significantly with
weight loss (
aldosterone: 853+/-156-635+/-73 pmol/l;
renin: 35.4+/-7-24+/-3 mU/l, both p<0.05). The volunteers were relatively
salt insensitive (mean arterial pressure change with
salt intake: 4 mmHg) and this was not affected by
weight loss. Moderate
weight loss had no effect on 24-hour urine free
cortisol/
cortisone, or on basal, or
ACTH-stimulated free and total
cortisol, or
CBG. Hence this conventional weight loss program reduces blood pressure and activity of the RAAS via an effect on
renin release. Despite various described influences of fat mass and energy restriction on HPA axis function, there were no changes in basal and stimulated HPA axis function with moderate
weight loss. There may be a threshold effect of
weight loss/energy restriction required to alter HPA axis function, or moderate
weight loss may lead to a counterbalanced effect of stimulatory and inhibitory influences on HPA axis function.