Abstract
Time-Restricted Eating is an eating pattern based on the circadian rhythm which limits daily food intake (usually to ≤12 h/day), unique in that no overt restriction is imposed on the quality, nor quantity, of food intake. This paper aimed to examine the effects of two patterns of TRE, traditional TRE, and Ramadan fasting, on two markers of circadian rhythm, cortisol and melatonin. PubMed and Web of Science were searched up to December 2020 for studies examining the effects of time restricted eating on cortisol and melatonin. Fourteen studies met our inclusion criteria. All Ramadan papers found statistically significant decrease in melatonin (p < 0.05) during Ramadan. Two out of the three Ramadan papers noted an abolishing of the circadian rhythm of cortisol (p < 0.05). The non-Ramadan TRE papers did not examine melatonin, and cortisol changes were mixed. In studies comparing TRE to control diets, Stratton et al. found increased cortisol levels in the non-TRE fasting group (p = 0.0018) and McAllister et al. noted no difference. Dinner-skipping resulted in significantly reduced evening cortisol and non-significantly raised morning cortisol. Conversely, breakfast skipping resulted in significantly reduced morning cortisol. This blunting indicates a dysfunctional HPA axis, and may be associated with poor cardio-metabolic outcomes. There is a paucity of research examining the effects of TRE on cortisol and melatonin. The contrasting effect of dinner and breakfast-skipping should be further examined to ascertain whether timing the feeding window indeed has an impact on circadian rhythmicity.
Highlights
Time-Restricted Eating (TRE) is an eating pattern based on the circadian rhythm that gives the body a daily fasting period
Rather paradoxically, increased cortisol levels can occur by taking, rather than missing, a meal [44]. The mechanisms behind this are not well understood, but hypotheses surround the phenomenon point to: the complex endocrine interplay with insulin response and glucocorticoid secretion [45], and amino acids such as tryptophan, which is affected by dietary intake, have been implicated in increased cortisol secretion [46]. This phenomenon was observed in a study we reviewed by Witbracht et al (2015) [29], who observed that females who skipped breakfast exhibited significantly higher cortisol postprandially—especially at midday— than did the controls
This paper found a potential blunting of the circadian cortisol rhythm during Ramadan and a reduction in melatonin which could lead to poor sleep duration and quality, as suggested by these markers of circadian rhythm
Summary
Time-Restricted Eating (TRE) is an eating pattern based on the circadian rhythm that gives the body a daily fasting period. This involves limiting daily food intake to 8–12 h with an intention to prolong the time spent in a fasting state [1]. This form of fasting is unique as no overt restriction is imposed on the quality, nor quantity, of food intake [2]. Macronutrient content and time of food consumption have an influence on peripheral circadian oscillators [1,10,11,12]
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