Abstract
A growing body of evidence highlights the importance of the biological clock as a modulator of energy balance and metabolism. Recent studies in humans have shown that ingested calories are apparently utilised more efficiently in the morning than in the evening and this is manifest through improved weight loss, even under iso‐energetic calorie intake. The mechanisms behind this enhanced morning energy metabolism are not yet clear, although it may result from behavioural adaptations or circadian driven variations in physiology and energy metabolism. A major objective of the newly funded Big Breakfast Study therefore is to investigate the mechanistic basis of this amplified morning thermogenesis leading to enhanced weight loss, by exploring behavioural and physiological adaptations in energy expenditure alongside the underlying circadian biology. This report briefly discusses the current research linking meal timing, circadian rhythms and metabolism; highlights the research gaps; and provides an overview of the studies being undertaken as part of the Medical Research Council‐funded Big Breakfast Study.
Highlights
IntroductionThe recent Nobel Prize awarded to Jeffrey Hall, Michael Rosbash and Michael Young for their discoveries of the molecular basis of biological rhythms highlights the profound importance of circadian rhythms in biology (chronobiology)
The UK has been reported to have one of the highest evening energy intakes, with the proportion of daily energy intake increasing gradually across the day and dinner providing on average 40% of daily calories (Almoosawi et al 2016)
A number of postprandial metabolic processes show time of day variations, with faster gastric emptying, enhanced intestinal absorption, superior glucose tolerance and higher postprandial energy expenditure [Thermic Effect of Food (TEF): the increase in energy expenditure after meal consumption associated with the energy costs of nutrient digestion and storage] observed in the morning compared to the evening
Summary
The recent Nobel Prize awarded to Jeffrey Hall, Michael Rosbash and Michael Young for their discoveries of the molecular basis of biological rhythms highlights the profound importance of circadian rhythms in biology (chronobiology). A number of postprandial metabolic processes show time of day variations, with faster gastric emptying, enhanced intestinal absorption, superior glucose tolerance and higher postprandial energy expenditure [Thermic Effect of Food (TEF): the increase in energy expenditure after meal consumption associated with the energy costs of nutrient digestion and storage] observed in the morning compared to the evening. These factors may contribute to the observed elevated morning TEF, by influencing the release of nutrients into the intestines for absorption, and affecting the release of hormones and metabolites required for energy consuming processes of nutrient digestion and storage (Weststrate et al 1989; Romon et al 1993) It is not yet clear whether the day/night rhythm in gastrointestinal absorption rate is driven by the behavioural cycle or endogenous circadian biology, and no studies have considered how 24-hour variations in gastric emptying following a meal may differentially influence postprandial energy metabolism across a day. The underlying mechanisms contributing to meal-timeinduced differential energy expenditure are not yet clear and the variable components of daily energy expenditure have never been explicitly studied in terms of daily rhythms
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