The ability to upregulate fat oxidation at appropriate times such as during fasting, low to moderate intensity exercise and after a high fat meal, is popularly advocated. This is presumably due to the perception that a high capacity to utilise fat may improve (ultra) endurance performance and help in the regulation of body fat and metabolic diseases. In accordance, impaired fat use at rest has been associated with obesity and insulin resistance (Kelley et al., 1999). However, there is inconclusive and / or a lack of systematic evidence, especially in a large diverse range of adults, exploring: 1\) Whether whole body fat use during exercise is altered in individuals with overweight or obesity compared to lean individuals 3\) The intra-individual variability in whole-body fat use at rest and during exercise 4\) Physiological, metabolic, lifestyle and genetic characteristics that are associated with whole-body fat use at rest and during exercise Therefore, the objectives of this study are three-fold: 1. To explore whether whole body fat use is associated with body composition 2. To explore associations between whole-body fat use and physiological, metabolic, lifestyle and genetic variables 3. To assess the intra-individual variability of whole-body fat use. This study is an observational, exploratory cross-sectional study. A wide range of 'healthy' and 'at-risk of metabolic disease' adults will be recruited. Participants will be asked to visit a laboratory at the University of Bath four times. Visit 1 is a screening and study familiarisation visit. Visits 2 and 3 are to be completed within 7-14 days and involve lifestyle monitoring (dietary and physical activity), a one-off urine and blood sample, assessment of fuel use at rest and during exercise (the latter through an incremental graded cycling exercise test to exhaustion). Visit 4 is to assess body composition via a dual-energy x-ray absorptiometry (DEXA) scan in addition to an optional skeletal muscle and / or fat tissue biopsy.
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Maximal rate of whole-body fat oxidation (mg/kg FFM/min)
Timeframe: 7 - 14 days