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Comparative Study
. 2002 Aug;40(2):265-74.
doi: 10.1053/ajkd.2002.34504.

Effect of Low-Carbohydrate High-Protein Diets on Acid-Base Balance, Stone-Forming Propensity, and Calcium Metabolism

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Comparative Study

Effect of Low-Carbohydrate High-Protein Diets on Acid-Base Balance, Stone-Forming Propensity, and Calcium Metabolism

Shalini T Reddy et al. Am J Kidney Dis. .

Abstract

Background: Low-carbohydrate high-protein (LCHP) diets are used commonly for weight reduction. This study explores the relationship between such diets and acid-base balance, kidney-stone risk, and calcium and bone metabolism.

Methods: Ten healthy subjects participated in a metabolic study. Subjects initially consumed their usual non-weight-reducing diet, then a severely carbohydrate-restricted induction diet for 2 weeks, followed by a moderately carbohydrate-restricted maintenance diet for 4 weeks.

Results: Urine pH decreased from 6.09 (Usual) to 5.56 (Induction; P < 0.01) to 5.67 (Maintenance;P < 0.05). Net acid excretion increased by 56 mEq/d (Induction; P < 0.001) and 51 mEq/d (Maintenance; P < 0.001) from a baseline of 61 mEq/d. Urinary citrate levels decreased from 763 mg/d (3.98 mmol/d) to 449 mg/d (2.34 mmol/d; P < 0.01) to 581 mg/d (3.03 mmol/d; P < 0.05). Urinary saturation of undissociated uric acid increased more than twofold. Urinary calcium levels increased from 160 mg/d (3.99 mmol/d) to 258 mg/d (6.44 mmol/d; P < 0.001) to 248 mg/d (6.19 mmol/d; P < 0.01). This increase in urinary calcium levels was not compensated by a commensurate increase in fractional intestinal calcium absorption. Therefore, estimated calcium balance decreased by 130 mg/d (3.24 mmol/d; P < 0.001) and 90 mg/d (2.25 mmol/d; P < 0.05). Urinary deoxypyridinoline and N-telopeptide levels trended upward, whereas serum osteocalcin concentrations decreased significantly (P < 0.01).

Conclusion: Consumption of an LCHP diet for 6 weeks delivers a marked acid load to the kidney, increases the risk for stone formation, decreases estimated calcium balance, and may increase the risk for bone loss.

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