When people are “diagnosed” with adrenal fatigue because their free cortisol is low. About half of people who have low free cortisol, have higher than average levels of cortisol
metabolites (what we call “metabolised cortisol”) which implies they make average (or more) levels of cortisol. Lower levels of free cortisol does not mean your cortisol production is necessarily low.
People who are obese, have more than twice as much cortisol production as healthy controls (as measured by the total output of cortisol metabolites). Studies on stress usually show levels of cortisol increasing (due to the stressor) by less than two-fold.
Long-term stress will typically increase an individual’s cortisol output less than obesity. Free cortisol is, however higher with stress but not typically with obesity. The reason longterm stress (and chronically elevated cortisol) has such a profound effect, is mostly due to free cortisol working at the receptor level.