EFFECTS OF DIET ON PLASMA GLUCOSE, FREE FATTY ACIDS, AND AMINO ACIDS DURING AN ULTRAMARATHON 179

Abstract

The Iditasport is a human powered ultramarathon that takes place in the Alaska Wilderness in February of each year. Participants have the option to complete the race on foot (125 km), snowshoe (125 km), cross-country ski (250 km), or mountain bike (250 km). The purpose of this study was to determine the effect of diet on plasma metabolites and amino acids following the 1994 Iditasport. Eight of sixty-two competitors in the race participated in this investigation. Blood was collected by venipuncture before (PRE) and after(POST) the race. After completion of the event subjects also provided a complete recall of what they consumed during the event. Diets were analyzed using Nutritionist IV. Subjects took 30.6±5.1 hr to complete the event. Caloric intake of subjects during the event was 1090.4±186.4 kJ·hr-1 (71.3±6.3% CHO; 20.4±5.3% fat; 8.25±1.3% protein). Plasma glucose (GLU) decreased(PRE=135.4±12.2 mg·dL-1); POST=107.56 mg·dL-1; p=.04) and plasma free fatty acids (FFA) increased(PRE=0.45±0.05 mmol·L-1; POST=1.77±0.25 mmol·L-1; p=.003) following the event. Plasma free tryptophan(f-TRP) increased (PRE=3.49±.83 μmol·L-1; POST=17.66±2.85 μmol·L-1; p=.001) while plasma valine decreased (PRE=374.3±42.3 μmol·L-1; POST=273.1±38.4 μmol·L-1; p=.032) following the event. In comparison, plasma levels of isoleucine, leucine, and total branch-chain amino acids were unchanged following the event. Time to complete the event was significantly correlated with relative changes in f-TRP (r=.84, p=.009) and FFA (r=.76, p=.048) but not correlated with changes in GLU or caloric intake. The results of this investigation indicate that performance in the Iditasport may be influenced by specific nutritional practices. More specifically, it appears that nutritional manipulations which could limit increases in plasma f-TRP and FFA during the event may be beneficial.