J Physiol Pharmacol. 1996 Jun;47(2):361-71.

Effect of low-carbohydrate-ketogenic diet on metabolic and hormonal responses to graded exercise in men.

Langfort J, Pilis W, Zarzeczny R, Nazar K, Kaciuba-Uściłko H.

Department of Applied Physiology Medical Research Centre, Polish Academy of Sciences, Warsaw, Poland.

Abstract

Maximal oxygen uptake (VO2 max) and lactate threshold (LT) were measured during graded, incremental exercise in 8 healthy, untrained volunteers (aged 22 +/- 0.9 yrs) following 3 days on a control, mixed diet, or a ketogenic (50% fat, 45% protein and 5% carbohydrates) diet of equal energy content. Before and after exercise tests acid base balance, plasma 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 loads. Blood LA concentrations were lower before, during and after exercise. Post exercise blood pH, as well as pre-and post exercise base excess and bicarbonates were reduced. Resting beta-HB concentration was elevated to approx. 2.0 mM, and FFA to approx. 1.0 mM. During a 1 h recovery period beta-HB decreased to 0.85 mM (p < 0.01) after the ketogenic diet, while plasma FFA did not change after exercise under either conditions. Both the pre-and post-exercise levels of adrenaline, noradrenaline, and cortisol were enhanced, whilst plasma insulin concentration was decreased on the ketogenic diet.

It is concluded that the short-term ketogenic diet does not impair aerobic exercise capacity, as indicated by elevated VO2 max and LT. This may be due to increased utilization of beta-HB and FFA when carbohydrate stores are diminished. Stimulation of the sympatho-adrenal system, and cortisol secretion with reduced plasma insulin concentration seem to be of importance for preservation of working capacity.