Introduction: It is not clear whether impaired exercise lipid oxidation is associated with excess body-fat or changes in metabolic health often associated with the overweight/obese state. Mixed findings may reflect lack of control for key variables including: 1) acute energy balance and macronutrient composition of the diet; 2) intensity and duration of exercise; and 3) subject characteristics including fat-free mass (FFM), fitness and, perhaps most importantly, metabolic health (e.g., insulin resistance).

Purpose: To determine whether excess body-fat or loss of metabolic health is associated with altered fuel metabolism during exercise.

Methods: Eight metabolically healthy (FH- and ≤1 MetSyn) normal-weight (BMI, 19-24 kg∙m-2) (MHNW) and 8 overweight/obese (26-35 kg∙m-2) (MHO) sedentary adults, and 7 metabolically unhealthy (FH+ and ≥ 2 MetSyn) normal-weight (MUNW) and 7 overweight/obese (MUO) sedentary adults, controlled for age (18-45 yr), sex, and fitness level (≤ “average”), completed a 10-day weight-stable (controlled feeding) testing protocol that included measurement of V?O2peak, RMR, body-fat %, OGTT and lipid oxidation during 45 min of moderate-intensity cycling. ANCOVA with adjustment for rate of O2 consumption (ml∙min-1∙kgBW-1) was used with contrasts to compare indices of lipid oxidation among the four groups.

Results: Adjusted means over both sexes for lipid oxidation during exercise, expressed as rate (mg∙min-1∙kgFFM-1), RER and percent total energy expenditure were significantly different between groups (p<0.05). There was a significant difference between MHNW vs. MUO for all indices (p<0.05), and between MUNW vs. MHO for rate (p<0.025). Tukey post-hoc also revealed a significant difference between MHNW vs. MUNW for all indices.

Conclusion: We found that impaired exercise lipid oxidation previously ascribed to the overweight/obese state was specifically associated with the loss of metabolic health as opposed to the overweight/obese state per se.


A.D. Arad: None. F.J. DiMenna: None. H.D. Kittrell: None. H.R. Kissileff: None. J. Albu: None.

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