Cortisol-Mediated Energy Allocation and Its Implications for Body Composition in Physically Active Adults: A Narrative Review

Abstract

Background: The historical approach to metabolism as a simple equation of calories is insufficient to explain the intricate variety of hormones that affect partitioning of energy among tissues, including muscle, fat, and others. Stress is accompanied by a rise in the production of a glucocorticoid hormone of the adrenal cortex called cortisol, which is a master regulator of the allocation of energy during stress, but whose relationship to body composition is not mentioned so much in the guidance of nutrition and training plans in practice.

Methods: A review was conducted to synthesize the studies from the past 20 years examining the effect of exercise, energy status, and body composition on cortisol in various populations of physically active adults.

Result. Energy availability had the largest impact on cortisol. Decreases in energy always increased levels of cortisol and decreased anabolic hormones such as the Insulin-like Growth Factor-1 (IGF-1) and Testosterone. There was no significant difference in resting cortisol between different training status or competitive level, suggesting that cortisol's response to exercise or stress and the daily cortisol rhythm are more informative biomarkers. Inactive obese individuals have low cortisol, whereas more active or under-stressed obese individuals have higher cortisol levels. People with major depressive disorder or hypothyroidism show weak or no cortisol response to exercise; this means findings from healthy people do not apply to everyone. Importantly, a reduction in cortisol levels in response to stress is not necessarily an indicator of overtraining, as it may be a normal adaptive response. In a male athlete, testosterone is the primary hormone that regulates body fat, while higher body fat percentages may aid in adaptation through being a reservoir of cortisol. Moreover, vigorous exercise was shown to have a negative feedback effect on subsequent stress responses, and the location of the competition games was shown to have a significant effect on post-game cortisol, with home games showing a greater stress response irrespective of the result.

Conclusions: Resting cortisol is a poor marker of training status, and energy availability is the most important factor determining cortisol regulation. The interpretation of cortisol response should take into account energy status, performance outcomes, and individual health status. In athletes and clinical populations, monitoring levels of reactive cortisol in addition to the testosterone/cortisol ratio may be a more effective way to assess stress, recovery, and adaptation.