Fat metabolism in formerly obese women: effect of exercise on
substrate oxidation and adipose tissue lipolysis.
Ranneries, Claudia, Jens B[umlaut]ulow, Benjamin Buemann, Niels Juel
Christensen, Joop Madsen, Arne Astrup.
Research Department of Human Nutrition, The Royal Veterinary and
Agricultural University, Frederiksberg, Denmark, Department of
Clinical Physiology/Nuclear Medicine, Bispebjerg Hospital,
Copenhagen, Denmark, Department of Internal Medical and
Endocrinology, Herlev Hospital, Denmark, Institute of Medical
Physiology, Panum Institute, University of Copenhagen, Denmark.
APStracts 4:0224E, 1997.
An impaired fat oxidation has been implicated to play a role in the
etiology of obesity, but it is unclear to what extent impaired fat
mobilization from adipose tissue or oxidation of fat is responsible.
The present study aimed to examine fat mobilization from adipose
tissue and whole body fat oxidation stimulated by exercise in 7
formerly obese women (FO) and 8 matched controls (C). Lipolysis in
the periumbilical subcutaneous adipose tissue, whole body energy
expenditure (EE) and substrate oxidation rates were measured before,
during and after a 60 min bicycle exercise bout of moderate
intensity. Lipolysis was assesed by glycerol release using
microdialysis and blood flow measurement by 133xenon clearance
technique. The FO women had lower resting EE than C (3.77 +/- 1.01
vs. 4.88 +/- 0.74 kJ/min, P < 0.05), but responded similarly to
exercise. Adipose tissue glycerol release was twice as high in FO
than in C at rest (0.455 +/- 0.299 vs. 0.206 +/- 0.102 [mu]mol/100g .
min, P < 0.05), but increased similarly in FO and C in response to
exercise._ In spite of higher plasma NEFA in FO (P < 0.001), fat
oxidation rates during rest and recovery were lower in FO than in C
(1.32 +/- 0.84 vs 3.70 +/- 0.57 kJ/min, P < 0.02), and fat
oxidation for a given plasma NEFA concentration was lower at rest (P
< 0.001) and during exercise (P= 0.01) in the formerly obese group.
In conclusion, fat mobilization both at rest and during exercise is
intact in FO, whereas fat oxidation is subnormal in spite of higher
circulation NEFA levels. The lower resting EE and the failure to
utilize fat as fuel contributes to a positive fat balance and weight
gain in formerly obese subjects.
Received 30 December 1996; accepted in final form 1 October 1997.
APS Manuscript Number E631-6.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 29 October 1997