Impaired plasma fatty acid oxidation in extremely obese women.

Skeletal muscle from extremely obese individuals exhibits decreased lipid oxidation compared with muscle from lean controls. It is unknown whether this effect is observed in vivo or whether the phenotype is preserved after massive weight loss. The objective of this study was to compare free fatty acid (FFA) oxidation during rest and exercise in female subjects who were either lean [n = 7; body mass index (BMI) = 22.6 +/- 2.2 kg/m(2)] or extremely obese (n = 10; BMI = 40.8 +/- 5.4 kg/m(2)) or postgastric bypass patients who had lost >45 kg (weight reduced) (n = 6; BMI = 33.7 +/- 9.9 kg/m(2)) with the use of tracer ([(13)C]palmitate and [(14)C]acetate) methodology and indirect calorimetry. The lean group oxidized significantly more plasma FFA, as measured by percent fatty acid uptake oxidized, than the extremely obese or weight-reduced group during rest (66.6 +/- 14.9 vs. 41.5 +/- 16.4 vs. 39.9 +/- 15.3%) and exercise (86.3 +/- 11.9 vs. 56.3 +/- 22.1 vs. 57.3 +/- 20.3%, respectively). BMI significantly correlated with percent uptake oxidized during both rest (r = -0.455) and exercise (r = -0.459). In conclusion, extremely obese women and weight-reduced women both possess inherent defects in plasma FFA oxidation, which may play a role in massive weight gain and associated comorbidities.