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Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri 63110
We evaluated plasma fatty acid
availability and plasma and whole body fatty acid oxidation during
exercise in five lean and five abdominally obese women (body mass
index = 21 ± 1 vs. 38 ± 1 kg/m2), who were
matched on aerobic fitness, to test the hypothesis that obesity alters
the relative contribution of plasma and nonplasma fatty acids to total
energy production during exercise. Subjects exercised on a
recumbent cycle ergometer for 90 min at 54% of their peak oxygen
consumption. Stable isotope tracer methods
([13C]palmitate) were used to measure fatty acid rate of
appearance in plasma and the rate of plasma fatty acid oxidation, and
indirect calorimetry was used to measure whole body substrate
oxidation. During exercise, palmitate rate of appearance increased
progressively and was similar in obese and lean groups between 60 and
90 min of exercise [3.9 ± 0.4 vs. 4.0 ± 0.3 µmol · kg fat free mass
(FFM)
1 · min
1]. The rate of plasma
fatty acid oxidation was also similar in obese and lean subjects
(12.8 ± 1.7 vs. 14.5 ± 1.8 µmol · kg
FFM
1 · min
1; P = not
significant). However, whole body fatty acid oxidation during exercise
was 25% greater in obese than in lean subjects (21.9 ± 1.2 vs.
17.5 ± 1.6 µmol · kg
FFM
1 · min
1; P < 0.05).
These results demonstrate that, although plasma fatty acid availability
and oxidation are similar during exercise in lean and obese women,
women with abdominal obesity use more fat as a fuel by oxidizing more
nonplasma fatty acids.
lipolysis; fat oxidation; intramuscular triglyceride; stable isotopes
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