Twenty-Four Hour Total and Dietary Fat Oxidation in Lean, Obese and Reduced-Obese Adults with and without a Bout of Exercise

Abstract

BackgroundIt has been hypothesized that obese and reduced-obese individuals have decreased oxidative capacity, which contributes to weight gain and regain. Recent data have challenged this concept.ObjectiveTo determine (1) whether total and dietary fat oxidation are decreased in obese and reduced-obese adults compared to lean but increase in response to an acute exercise bout and (2) whether regular physical activity attenuates these metabolic alterations.DesignWe measured 24-hr total (whole-room calorimetry) and dietary fat (14C-oleate) oxidation in Sedentary Lean (BMI = 21.5±1.6; n = 10), Sedentary Obese (BMI = 33.6±2.5; n = 9), Sedentary Reduced-Obese (RED-SED; BMI = 26.9±3.7; n = 7) and in Physically Active Reduced-Obese (RED-EX; BMI = 27.3±2.8; n = 12) men and women with or without an acute exercise bout where energy expended during exercise was not replaced.ResultsAlthough Red-SED and Red-EX had a similar level of fatness, aerobic capacity and metabolic profiles were better in Red-EX only compared to Obese subjects. No significant between-group differences were seen in 24-hr respiratory quotient (RQ, Lean: 0.831±0.044, Obese: 0.852±0.023, Red-SED: 0.864±0.037, Red-EX: 0.842±0.039), total and dietary fat oxidation. A single bout of exercise increased total (+27.8%, p<0.0001) and dietary (+6.6%, p = 0.048) fat oxidation across groups. Although exercise did not impact RQ during the day, it decreased RQ during sleep (p = 0.01) in all groups. Red-EX oxidized more fat overnight than Red-SED subjects under both resting (p = 0.036) and negative energy balance (p = 0.003) conditions, even after adjustment for fat-free mass.ConclusionObese and reduced-obese individuals oxidize as much fat as lean both under eucaloric and negative energy balance conditions, which does not support the hypothesis of reduced oxidative capacity in these groups. Reduced-obese individuals who exercise regularly have markers of metabolic health similar to those seen in lean adults. Both the acute and chronic effects of exercise were primarily observed at night suggesting an important role of sleep in the regulation of lipid metabolism.

Comparison of Diet versus Exercise on Metabolic Function and Gut Microbiota in Obese Rats

“…HFD has been shown to reduce SPA (40); the present data suggest that inducing an energy deficit by any means might lessen the SPA-reducing effect of HFD, and that Ex may be especially protective in this regard. Ex also increased fat oxidation, as indicated by lower RQ values in both cycles whereas WM did not affect fat oxidation; similar exercise-specific effects on RQ have been reported in humans (3). …”

The Importance of Fatty Acids as Nutrients during Post-Exercise Recovery

“…However, when the exercise-induced energy deficit was compensated for by an intake of meals following exercise on the exercise day, elevated overnight-fasted FA levels, and lower RER values were still evident the day following exercise [4]. Furthermore, afternoon exercise led to increased nocturnal FA oxidation despite the intake of evening meals [36]. Thus, exercise seems to affect substrate utilization independently of exercise-induced energy deficit.…”

Age-related changes in basal substrate oxidation and visceral adiposity and their association with metabolic syndrome

“…Previous studies have investigated the association of either basal RQ or fat oxidation with body weight, BMI or FM [5,14,23,[35][36][37][38][39][40][41]. The majority of these studies were cross-sectional [5,14,23,35,36,[38][39][40]42]. The two most relevant longitudinal studies on this topic were conducted by Zurlo et al [41] and Seidell et al [37].…”

“…The study of the association between substrate oxidation and cardiovascular risk factors [(i.e. glucose, triglycerides, insulin, free fatty acids (FFAs)] [7,[14][15][16][17][18][19][20][21] is often a secondary objective, which may impact on the statistical power and selective presentation of results. In the last 10 years, a handful of studies have explored the association of basal substrate oxidation with chronic disease risk.…”