A Time to Eat and a Time to Exercise

Evelyn B. Parr; Leonie K. Heilbronn; John A. Hawley


Exerc Sport Sci Rev. 2020;48(1):4-10. 

In This Article

Abstract and Introduction


This Perspective for Progress provides a synopsis for the potential of time-restricted eating (TRE) to rescue some of the deleterious effects on circadian biology induced by our modern-day lifestyle. We provide novel insights into the comparative and potential complementary effects of TRE and exercise training on metabolic health.


Numerous metabolic and physiological processes are underpinned by 24-h biological oscillations that are under the control of a central circadian clock, present in all mammalian cells.[1] Synchronization of the expression of circadian clock genes in the suprachiasmatic nucleus (SCN) of the hypothalamus is primarily governed by the light-dark cycle.[1] However, other environmental and behavioral time cues, termed "zeitgebers," such as the timing of meals and exercise, along with sleep-wake cycles, can "fine-tune" the central clock.[2] These nonphotic cues can reset or induce time-phase shifts in circadian oscillations through mechanisms independent of the SCN.[3,4] Indeed, our prevailing modern lifestyle (round-the-clock access to energy-dense food, low levels of habitual physical activity accompanied by periods of prolonged sitting, and inadequate quality/quantity of sleep) interacts with underlying biology to create an environment in which circadian rhythms are disrupted, often resulting in a plethora of metabolic conditions.[3–5] This was not always the case.

Throughout human evolution, lifestyle and energy availability were inextricably linked to the periodic cycles of feasts and famines. During these natural cycles, specific genes evolved to regulate efficient storage of endogenous fuel stores, so-called thrifty genes.[6] During the early hunter-gatherer period, there was also the selection of genes and traits to support a "physical activity cycle",[7,8] and under these constraints, most of the present human genome evolved. Today, those alleles and traits that evolved for energy storage and locomotion are exposed to a host of unfavorable environment cues over an extended lifespan, perturbing the intrinsic circadian clock and increasing the risk of many lifestyle-induced metabolic diseases.[3–5] In this Perspective for Progress, we provide a synopsis of the efficacy of diet and exercise interventions to rescue many of the deleterious effects on circadian biology induced by our modern-day lifestyle. We describe new insights into the comparative and potential complementary effects of exercise training and a novel dietary intervention that encourages a longer daily duration of fasting to improve human metabolic health, but argue that exercise still remains the optimal strategy to improve the majority of lifestyle-induced disorders in metabolism.