Substrate oxidation and thyroid hormone response to the introduction of a high fat diet in formerly obese women.
OBJECTIVE
To investigate the adaptation in substrate utilization to a sudden change in dietary composition from a medium fat to a high fat diet, during a three day period in formerly obese and never obese women.


METHODS
Energy expenditure (EE) and substrate oxidation rates were measured in eight healthy formerly obese women and eight never obese controls, during four consecutive days in a respiration chamber. The first day and the day prior to the experiment, the subjects consumed a diet with 30 energy-% fat, whereas the diet had 55 energy-% fat on the subsequent three days.


RESULTS
The rate of adjustment of oxidative substrate partitioning expressed as 24 h non-protein respiratory quotient (RQnp) was similar in the two groups. RQnp on each of the days was also similar between the two groups, after accounting for a group difference in energy balance, caused by a non-significantly lower EE in the formerly obese women. However, the formerly obese subjects, demonstrated a greater suppression of postprandial fat oxidation after supper, which was unrelated to energy balance. Furthermore, the formerly obese subjects, in contrast to the controls, exhibited a reduction in plasma triiodothyronine/thyroxine ratio (T3/T4) following the high fat diet. A positive correlation between T3/T4 and EE was found in the 16 subjects.


CONCLUSIONS
The formerly obese subjects did not show a slower adaptation rate of substrate utilization when challenged with a high fat diet, but exhibited an enhanced suppression of fat oxidation and a lower T3/T4 ratio after supper, when fed a high fat diet.
Research Department of Human Nutrition, The Royal Veterinary and Agricultural University, Frederiksberg, Denmark.
B
B
Buemann
S
S
Toubro
A
A
Astrup
D000328:Adult; D004041:Dietary Fats / Q000008:administration & dosage* / Q000378:metabolism*; D002149:Energy Intake; D004734:Energy Metabolism; D005260:Female; D006339:Heart Rate; D006801:Humans; D007700:Kinetics; D008875:Middle Aged; D009765:Obesity / Q000378:metabolism*; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D005082:Physical Exertion; D013963:Thyroid Hormones / Q000097:blood*; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
D004041:Dietary Fats; D013963:Thyroid Hormones; D014284:Triiodothyronine; D013974:Thyroxine