The effect of fitness on energy metabolism in lean and obese healthy men

Abstract

This study was designed to assess the independent contributions of cardiorespiratory fitness (CRF) and adiposity to the metabolic health of obese individuals. It specifically focused on how body composition and CRF affect the relative contribution of glucose, fat and protein to energy production (EP) in resting state as well as during and after exercise. Eight obese fit (OF – 30±12 yrs., 178±6 cm, 105±8 kg) and eight lean fit (LF – 36±9 yrs., 181±5 cm, 82±5 kg) were screened for medical conditions and food/health supplement use and partook in two sessions – separated by 72 hr – that consisted of the following measurements: (1) a basal metabolic rate (BMR) in a fasting state for the determination of substrate oxidation (baseline) followed by an incremental running test for the determination of V̇O₂max and of exercise intensity that elicits maximal fat oxidation (MFO); (2) a BMR, an iso-caloric (300 kcal expenditure) treadmill exercise at MFO, a post-exercise metabolic rate (PEMR) in fasting state (30 min after exercise), and two PEMR in the fed state at 90 and 150 min after exercise. The fed state was achieved by a 300 kcal meal provided immediately after the first PEMR. Food intake and physical activity were monitored throughout the study. Although statistical significance was found in %FAT (p<0.001) between both groups (35±4% and 18±4 % for OF and LF, respectively), no differences were detected in V̇O₂max (OF:4.1±0.5 L·min⁻¹ and LF:4.2±0.5 L·min⁻¹) and V̇O₂MFO (OF:1.6±0.4 L·min⁻¹ and LF:1.8±0.5 L·min⁻¹) confirming CRF between-groups homogeneity. Further to these results, participants showed no substrate oxidation differences before, during, and after exercise. In conclusion, obese fit individuals display a pattern of substrate partitioning comparable to that observed in lean fit individuals, confirming that fitness can modulate the metabolic impacts of obesity and could reduce the risks of chronic diseases associated with obesity.