Effect of Carbohydrate-Electrolyte Solution Including Bicarbonate Ion Ad Libitum Ingestion on Urine Bicarbonate Retention during Mountain Trekking: A Randomized, Controlled Pilot Study.

We investigated whether bicarbonate ion (HCO3-) in a carbohydrate-electrolyte solution (CE+HCO3) ingested during climbing to 3000 m on Mount Fuji could increase urine HCO3- retention. This study was a randomized, controlled pilot study. Sixteen healthy lowlander adults were divided into two groups (six males and two females for each): a tap water (TW) group (0 kcal with no energy) and a CE+HCO3 group. The allocation to TW or CE+HCO3 was double blind. The CE solution contains 10 kcal energy, including Na+ (115 mg), K+ (78 mg), HCO3- (51 mg) per 100 mL. After collecting baseline urine and measuring body weight, participants started climbing while energy expenditure (EE) and heart rate (HR) were recorded every min with a portable calorimeter. After reaching a hut at approximately 3000 m, we collected urine and measured body weight again. The HCO3- balance during climbing, measured by subtracting the amount of urine excreted from the amount of fluid ingested, was -0.37 ± 0.77 mmol in the CE+HCO3, which was significantly higher than in the TW (-2.23 ± 0.96 mmol, p < 0.001). These results indicate that CE containing HCO3- supplementation may increase the bicarbonate buffering system during mountain trekking up to ~3000 m, suggesting a useful solution, at least, in the population of the present study on Mount Fuji.