Primarily experimental evidence suggests that endogenous glucocorticoids may be suppressed by adipocyte-derived leptin and elevated by dietary acidity. Therefore, we examined whether these factors may also be relevant in healthy adults on unrestricted diets. For this we used a new methodological approach in which potentially bioactive free glucocorticoids were determined as the sum of urinary free cortisol and urinary free cortisone and that also takes into account total adrenal glucocorticoid secretion assessed by the sum of the 3 major urinary glucocorticoid metabolites tetrahydrocortisone, tetrahydrocortisol, and 5alpha-tetrahydrocortisol. Body composition, plasma cortisol, plasma leptin, and 24-h urinary excretion rates of net acid and glucocorticoid metabolites were examined cross-sectionally in 30 healthy adults (15 women; 22-44 y old; BMI 20-25 kg/m2). Plasma leptin, percentage body fat, and body surface area-corrected adrenal glucocorticoid secretion showed the usual sex dimorphism (male vs. female, P < 0.05 in each case: 2.8 +/- 1.6 microg/L vs. 7.6 +/- 4.9 microg/L, 16.8 +/- 4.2% vs. 26.9 +/- 4.9%, and 5.1 +/- 1.6 mg x m(-2) x d(-1) vs. 4.0 +/- 1.3 mg x m(-2) x d(-1), respectively), whereas net acid excretion, plasma cortisol, and potentially bioactive free glucocorticoids did not differ between the sexes. Potentially bioactive free glucocorticoids correlated positively with body fat and leptin in men (P < 0.05) but not in women. After adjustment for total adrenal glucocorticoid secretion, net acid excretion was a positive and leptin a negative predictor (P < 0.05) of potentially bioactive free glucocorticoids in women only (total explained variability R2 = 0.71). Our findings indicate that, at least in women, variability of potentially bioactive free glucocorticoids is not only explained by adrenal glucocorticoid secretion but is also metabolically affected by circulating leptin and diet-dependent net acid excretion.