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 (HCO) in a carbohydrate-electrolyte solution (CE+HCO) ingested during climbing to 3000 m on Mount Fuji could increase urine HCO 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), HCO (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 HCO 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, < 0.001). These results indicate that CE containing HCO 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.