Nutrient timing, metabolism, and health in humans

  • Harry Smith

Student thesis: Doctoral ThesisPhD

Abstract

Biological rhythms in physiological and behavioural processes anticipate regular environmental changes and therefore adjust physiology and behaviour accordingly. These biological rhythms appear to facilitate the response of skeletal muscle to variable nutrient supply. The timing and/or distribution of nutrients across the day could conceivably alter biological rhythms in this tissue, which could be associated with metabolic health outcomes. However no human research to date has characterised temporal rhythms in in vivo human muscle alongside systemic markers of metabolism. Furthermore, recent studies have revealed links between the first meal of the day and human health, so it is now important to examine the potential underlying mechanisms of these relationships. The aim of this thesis was to take a multi-faceted approach to studying the metabolic and behavioural effects of meal timing, with focus on both absolute and relative timing. Initially, Chapter 4 provided 24-h characterisation of diurnal rhythms in human skeletal muscle gene expression alongside circulating metabolic and endocrine markers. Chapter 5 then built on this by demonstrating the ability of enteral feeding pattern (i.e., continuous versus bolus nutrient delivery) to affect rhythms in skeletal muscle and circulating metabolites – for example, revealing that systemic glucose and NEFA are primarily driven by 24 h profiles of insulin. Chapter 6 confirmed that next morning metabolic control is not affected by hourly sleep fragmentation but is affected when coffee is consumed to remedy a poor night of sleep. The acute experiment described in Chapter 7 demonstrated that enrichment of a typical carbohydrate-rich breakfast with whey protein effectively elicited the second-meal effect but did not differentially alter diet-induced thermogenesis or appetite above that of a carbohydrate-rich breakfast. Finally, Chapter 8 showed that regular daily consumption of that protein-enriched breakfast did not meaningfully alter the major components of energy balance, nor did it change postprandial metabolism or appetite relative either to regular daily consumption of a typical carbohydrate-rich breakfast or daily extended morning fasting. Collectively the research in this thesis highlights the effects of nutrient timing in both absolute terms (i.e., in relation to clock time) and relative terms (i.e., in relation to other daily events) – with implications for how the scheduling of daily meals and nutrients can affect the acute and chronic regulation of metabolism and behaviour.
Date of Award18 Jan 2023
Original languageEnglish
Awarding Institution
  • University of Bath
SupervisorJames Betts (Supervisor), James Turner (Supervisor), Javier Gonzalez (Supervisor), Jean-Philippe Walhin (Supervisor) & Dylan Thompson (Supervisor)

Keywords

  • circadian rhythms
  • nutrient metabolism
  • carbohydrate
  • protein
  • postprandial
  • fasting
  • skeletal muscle
  • RNA

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