When to eat and when to exercise : the impact of timing on energy balance and obesity

The prevalence of obesity and associated disorders continues to increase worldwide at an alarming rate. Many of the current treatment and preventative strategies focus on manipulating energy balance through diet (decreasing energy intake (EI)) and exercise (increasing energy expenditure (EE)). While this is undoubtedly the gold standard approach, lack of adherence and weight regain is a common occurrence. Sustainable weight management approaches are required to help flatten the curve of the obesity crisis. In recent decades interest has grown around the timing of eating and the timing of exercise because of the influence they have on circadian rhythms which are present in most physiological and metabolic processes. Therefore, the aim of this thesis was to investigate the impact of the timing of eating and timing of exercise on energy balance and body weight management. A systematic review (Chapter 2) of timing of eating (n=38) and timing of exercise (n=7) studies in overweight and obese individuals found that dietary protocols that employed earlier eating may result in greater reductions in body weight than later eating protocols, while the findings of the effect of timing of exercise were limited by the availability of research, highlighting the need for further studies in this area, particularly regarding the interaction between timing of eating and timing of exercise on appetite regulation. A cross-sectional study of a UK representative population (n=2526 adults) (Chapter 3) observed that energy intake in the afternoon was inversely related to total EI, while eating in the evening may be related to lower diet quality and greater alcohol intake. This highlighted the need for strategies that may help mitigate the drive towards eating in the evening. The Impact of Morning or Evening Exercise (TIME-EX) study (Chapter 4) was developed to assess the impact of the time of day of exercise on EI and food preference in physically inactive adults (n=12). In the total sample, EI and food preference did not differ between morning and evening exercise, however when analysed by gender, exercising in the morning resulted in a lower overall EI than evening exercise in males and this requires further investigation. This thesis has highlighted that the timing of eating and exercise may influence aspects of energy balance and metabolism. Eating the largest proportion of EI earlier in the day appears to be more beneficial than eating a larger proportion in the evening and may help reduce total EI. The time of day that exercise is completed could influence the timing of EI and total EI, but further research is needed on how this modifiable behaviour can be incorporated into weight management strategies.