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

This 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.