Eat, Train, Sleep-Retreat? Hormonal Interactions of Intermittent Fasting, Exercise and Circadian Rhythm

Abstract

The circadian rhythmicity of endogenous metabolic and hormonal processes is controlled by a complex system of central and peripheral pacemakers, influenced by exogenous factors like light/dark-cycles, nutrition and exercise timing. There is evidence that alterations in this system may be involved in the pathogenesis of metabolic diseases. It has been shown that disruptions to normal diurnal rhythms lead to drastic changes in circadian processes, as often seen in modern society due to excessive exposure to unnatural light sources. Out of that, research has focused on time-restricted feeding and exercise, as both seem to be able to reset disruptions in circadian pacemakers. Based on these results and personal physical goals, optimal time periods for food intake and exercise have been identified. This review shows that appropriate nutrition and exercise timing are powerful tools to support, rather than not disturb, the circadian rhythm and potentially contribute to the prevention of metabolic diseases. Nevertheless, both lifestyle interventions are unable to address the real issue: the misalignment of our biological with our social time.

Keywords: circadian rhythm; exercise; intermittent fasting; metabolism; stress hormones.

Figure 1

Different Stressors modify the normal diurnal rhythmicity. The circadian rhythm is controlled by the light/dark-cycle that influences the rhythmicity of central pacemaker (black) and thus all peripheral processes (red) are synchronized with each other (a). Different external stressors can lead to disturbances in the highly complex interaction of the central and peripheral oscillators. Damped responses of peripheral pacemakers (b) are observed especially in insulin resistance or night eating. High fat meals lead to prolonged cycles (c) and thus a shift of the periods against each other. Irregular rhythms (d) may be caused by irregular meals or generally an irregular lifestyle. A decoupling of the sleep/wake cycle from the light/dark cycle, as seen in shift work or due to modern lifestyle prolonged waking times, can additionally shift the periods against each other (e). A combination of several factors can result in a partial or complete decoupling of the peripheral from the central pacemaker (f).

Figure 2

Resetting the circadian clock. Sleep, time restricted feeding (TRF) and exercise affect circadian rhythmicity helping to resynchronize the central with peripheral pacemakers by influencing different metabolic pathways. Exercise particularly affects peripheral processes in muscle and adipose tissues and influences glucose homeostasis. In addition, regular exercise can reduce stress levels by influencing cortisol levels. Besides, glucose homeostasis and hunger/satiety hormones are controlled by TRF. Despite these peripheral influences, sleep also affects central rhythmicity through a direct impact on melatonin and cortisol secretion.