Changes in Serum Cortisol Levels After 10 Days of Overfeeding and Fasting
OBJECTIVE: Chronic caloric deprivation and obesity are complicated by hypercortisolemia. The effects of acute overfeeding and fasting on circulating free cortisol levels and conversion of cortisone to free cortisol are unknown. We hypothesized that serum free cortisol and free cortisol-to-cortisone ratio would increase after both overfeeding and fasting. RESEARCH DESIGN AND METHODS: Prospective study of 22 healthy volunteers who completed a 10-day high-calorie protocol followed by a 10-day fast, separated by a 2-week wash-out. Morning free and total cortisol and free cortisone levels (LC/MS) were performed at baseline and after 10 days of each intervention. RESULTS: Both high-calorie feeding and fasting increased total and free cortisol and the free cortisol-to-free cortisone ratio (p=0.001 to p=0.046). There were sex interactions, with significant effects in men (p<0.001), but not women (p=0.898 and 1.000, respectively) in subset analyses examining the effects of fasting on free cortisol and the free-to-total cortisol ratio. CONCLUSION: Overfeeding and fasting both increase circulating free cortisol levels and appear to alter the balance between cortisol and its inactive metabolite, cortisone. Further study is warranted to determine whether elevated cortisol levels contribute to complications of starvation and obesity, such as bone fragility.