Optimising intermittent fasting: Evaluating the behavioural and metabolic effects of extended morning and evening fasting

D J Clayton,T Slater,W J A Mode

doi:10.1111/nbu.12467

Abstract

AbstractThis article describes the aims of a new study funded by the British Nutrition Foundation Drummond Pump Priming Award. This study will explore the independent metabolic, endocrinal and behavioural effects of extended morning and evening fasting. In an obesogenic society, there is an urgent need to identify effective strategies for preventing obesity‐related diseases, such as type 2 diabetes. Implementing extended periods of fasting and restricted time permitted for food intake may be an efficacious method for weight management and improving metabolic health. However, recent research suggests that the success of this intervention may be influenced by when the fasting window occurs, with evening fasting appearing to elicit superior metabolic benefits compared to morning fasting. The mechanisms driving these time‐dependent outcomes are not yet clear but may be due to circadian variations in metabolic physiology and in behaviours known to influence energy balance. To date, no study has directly compared the acute metabolic and behavioural responses to morning and evening fasting with those of a control trial. Research on evening fasting is also currently restricted to individuals living with overweight or obesity, emphasising a need for research in lean individuals aiming to maintain a healthy bodyweight and improve metabolic health. This article highlights the need for alternative nutritional interventions to improve public health, before reviewing the existing literature linking extended fasting, circadian rhythms and behavioural and metabolic outcomes. The final part of this article outlines the aims, methodology and intended outcomes of the current research project.

Highlights

Sixty-three per cent of the UK population are living with overweight or obesity and are at increased risk of numerous metabolic diseases, making this a significant public health priority (NHS Digital 2020)
Weight loss requires the creation of an energy deficit, typically achieved by reducing energy intake and/or increasing energy expenditure
Mean fasting blood glucose concentrations over the intervention period were reduced following evening fasting only. These findings provide some support to the notion that reducing the window between the first and final meal of the day can improve metabolic profile, but advancing the final meal may be preferable for 24hour glucose control

Summary

Introduction

Sixty-three per cent of the UK population are living with overweight or obesity and are at increased risk of numerous metabolic diseases, making this a significant public health priority (NHS Digital 2020). Numerous metabolic markers display 24-hour circadian variations, including plasma lipids (Morgan et al 1999) and insulin sensitivity (Saad et al 2012), which appears to ameliorate in the morning and decline in the evening This suggests that time-restricted eating interventions restricting energy intake to an earlier eating window may be efficacious for health. Rodent studies have shown that restricting feeding to the early hours of the active phase can elicit numerous health benefits, including improvements in insulin sensitivity and blood lipid profile, and resistance to weight gain (Hatori et al 2012) In rodents, these effects may be partly driven by increased 24-hour energy expenditure when meals are consumed exclusively within the early active phase (Hatori et al 2012), but a similar effect does not appear to occur in humans. Based on the outlined evidence and data in UK adults showing that ~ 40% of daily energy intake is consumed in the evening (Almoosawi et al 2016), the principal hypothesis for this study is that evening fasting will reduce energy intake and elevate markers of appetite, but will improve glycaemic control, relative to morning fasting and a control trial

Methodology

Findings

Conclusions