Effect of low-carbohydrate high-protein diets on acid-base balance, stone-forming propensity, and calcium metabolism.
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).


CONCLUSIONS
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.
Reddy
Shalini T
ST
Department of Internal Medicine, Section of General Internal Medicine, The University of Chicago, IL 60637, USA. sreddy@medicine.bsd.uchicago.edu
Wang
Chia-Ying
CY
Sakhaee
Khashayar
K
Brinkley
Linda
L
Pak
Charles Y C
CY
D000137:Acid-Base Imbalance / Q000139:chemically induced / Q000378:metabolism*; D000328:Adult; D015992:Body Mass Index; D001842:Bone and Bones / Q000378:metabolism; D002118:Calcium / Q000097:blood / Q000378:metabolism* / Q000652:urine; D004040:Dietary Carbohydrates / Q000378:metabolism; D004044:Dietary Proteins / Q000009:adverse effects*; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007669:Kidney Calculi / Q000097:blood / Q000139:chemically induced / Q000378:metabolism* / Q000652:urine; D008297:Male; D008875:Middle Aged
D004040:Dietary Carbohydrates; D004044:Dietary Proteins; D002118:Calcium
Non-programmatic