Effects of severe diet restriction on the oxygen consumption of obese women during exercise

Eleven moderately obese, but otherwise healthy, young women were studied for three days while being fed their normal, unrestricted diet and then again for a two week period while being fed an energy-restricted, high-protein diet--220 kcal (0.92 MJ)/day as casein. Oxygen consumption (VO2) was measured 32 times for each subject, both at rest and during bicycle exercises. For each subject oxygen consumption was significantly lower, at rest and during moderate exercise, when the subjects were being fed the restricted diet. There was no significant difference among the diet treatments at the highest activity levels. The explanation proposed (though without experimental proof) is that, during the restricted diet, the increased reverse triiodothyronine (rT3) would result in a decrease of the aerobic glycolysis and no change in the anaerobic glycolysis.