Fat oxidation during exercise: significance, determinants and response to nutrition

There is a large inter-subject variability in the capacity to oxidise fat (MFO) during exercise and this could have important implications for metabolic health. Chapter 3 of this thesis was designed to explore the relationship between MFO with 24-h fat oxidation and insulin sensitivity. This study showed that MFO during exercise is significantly and positively associated with 24-h fat oxidation and insulin sensitivity. Chapter 4 investigated relationships between selected plasma metabolites, hormones and overnight-fasted resting fat oxidation rates, with MFO. Plasma lipolytic markers, plasma insulin, resting fat oxidation and aerobic capacity were important modulators of the inter-subject variability in MFO. Chapter 5 explored the influence of meal timing around exercise on substrate utilisation, lipolytic markers and insulin, and intra-muscular triglyceride (IMTG) use in obesity. This study found that Fasted- as compared with Fed-state exercise augments exercise fat oxidation, and the circulating concentration of plasma glycerol and NEFA during exercise. This thesis generates new data that contributes to our understanding of the links between MFO and metabolic risk, as well as the factors that influence the inter-subject variability in MFO during exercise. It also shows that fasted exercise augments exercise fat oxidation, which could have meaningful implications for optimising metabolic health