EFFECT OF LOW-CARBOHYDRATE - KETOGENIC DIET ON METABOLIC AND HORMONALRESPONSES TO GRADED-EXERCISE IN MEN

Maximal oxygen uptake (VO2 max) and lactate threshold (LT) were measur ed during graded, incremental exercise in 8 healthy, untrained volunte ers (aged 22 +/- 0.9 yrs) following 3 days on a control, mixed diet, o r a ketogenic (50% fat, 45% protein and 5% carbodydrates) diet of equa l energy content. Before and after exercise tests acid base balance, p lasma beta-hydroxybutyrate (beta-HB), free fatty acid (FFA), and some hormone concentrations were determined. In comparison with the normal diet, the ketogenic diet resulted in: an increased VO2 max, decreased respiratory exchange ratio an a shift of LT towards higher exercise lo ads. Blood LA concentrations were lower before, during and after exerc ise. Post exercise blood pH, as well as pre-and post exercise base exc ess and bicarbonates were reduced. Resting beta-HB concentration was e levated to approx. 2.0 mM, and FFA to approx. 1.0 mM. During a 1 h rec overy period beta-HB decreased to 0.85 mM (p < 0.01) after the ketogen ic diet, while plasma FFA did not change after exercise under either c onditions. Both the pre-and post-exercise levels of adrenaline, noradr enaline, and cortisol were enhanced, whilst plasma insulin concentrati on was decreased on the ketogenic diet. It is concluded that the short -term ketogenic diet does not impair aerobic exercise capacity, as ind icated by elevated VO2 max and LT. This may be due to increased utiliz ation of beta-HB and FFA when carbohydrate stores are diminished. Stim ulation of the sympatho-adrenal system, and cortisol secretion with re duced plasma insulin concentration seem to be of importance for preser vation of working capacity.