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Potassium Bicarbonate Attenuates the Urinary Nitrogen Excretion That Accompanies an Increase in Dietary Protein and May Promote Calcium Absorption

Jean Mayer United States Department of Agriculture Human Nutrition Research Center on Aging at Tufts University (L.C., S.S.H., H.M.R., G.E.D., B.D.-H.), Boston, Massachusetts 02111; and United States Department of Agriculture Children’s Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine and Texas Children’s Hospital (S.A.A.), Houston, Texas 77030

Address all correspondence to: Lisa Ceglia, M.D., Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, 711 Washington Street, Boston, Massachusetts 02111. E-mail: lisa.ceglia{at}tufts.edu. Reprints will not be available.

Context: Protein is an essential component of muscle and bone. However, the acidic byproducts of protein metabolism may have a negative impact on the musculoskeletal system, particularly in older individuals with declining renal function.

Objective: We sought to determine whether adding an alkaline salt, potassium bicarbonate (KHCO₃), allows protein to have a more favorable net impact on intermediary indices of muscle and bone conservation than it does in the usual acidic environment.

Design: We conducted a 41-d randomized, placebo-controlled, double-blind study of KHCO₃ or placebo with a 16-d phase-in and two successive 10-d metabolic diets containing low (0.5 g/kg) or high (1.5 g/kg) protein in random order with a 5-d washout between diets.

Setting: The study was conducted in a metabolic research unit.

Participants: Nineteen healthy subjects ages 54–82 yr participated.

Intervention: KHCO₃ (up to 90 mmol/d) or placebo was administered for 41 d.

Main Outcome Measures: We measured 24-h urinary nitrogen excretion, IGF-I, 24-h urinary calcium excretion, and fractional calcium absorption.

Results: KHCO₃ reduced the rise in urinary nitrogen excretion that accompanied an increase in protein intake (P = 0.015) and was associated with higher IGF-I levels on the low-protein diet (P = 0.027) with a similar trend on the high-protein diet (P = 0.050). KHCO₃ was also associated with higher fractional calcium absorption on the low-protein diet (P = 0.041) with a similar trend on the high-protein diet (P = 0.064).

Conclusions: In older adults, KHCO₃ attenuates the protein-induced rise in urinary nitrogen excretion, and this may be mediated by IGF-I. KHCO₃ may also promote calcium absorption independent of the dietary protein content.