Pilot Study Examining the Influence of Potassium Bicarbonate Supplementation on Nitrogen Balance and Whole-Body Ammonia and Urea Turnover Following Short-Term Energy Restriction in Older Men.

With aging there is a chronic low-grade metabolic-acidosis that may exacerbate negative protein balance during weight loss. The objective of this randomized pilot study was to assess the impact of 90 mmol∙day potassium bicarbonate (KHCO₃) versus a placebo (PLA) on 24-h urinary net acid excretion (NAE), nitrogen balance (NBAL), and whole-body ammonia and urea turnover following short-term diet-induced weight loss. Sixteen (KHCO₃; = 8, PLA; = 8) older (64 ± 4 years) overweight (BMI: 28.5 ± 2.1 kg∙day) men completed a 35-day controlled feeding study, with a 7-day weight-maintenance phase followed by a 28-day 30% energy-restriction phase. KHCO₃ or PLA supplementation began during energy restriction. NAE, NBAL, and whole-body ammonia and urea turnover (N-glycine) were measured at the end of the weight-maintenance and energy-restriction phases. Following energy restriction, NAE was -9.8 ± 27.8 mmol∙day in KHCO₃ and 43.9 ± 27.8 mmol∙day in PLA ( < 0.05). No significant group or time differences were observed in NBAL or ammonia and urea turnover. Ammonia synthesis and breakdown tended ( = 0.09) to be higher in KHCO₃ vs. PLA following energy restriction, and NAE was inversely associated ( = -0.522; < 0.05) with urea synthesis in all subjects. This pilot study suggests some benefit may exist with KHCO₃ supplementation following energy restriction as lower NAE indicated higher urea synthesis.