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Citrate, malate, and akali concentrations in commonly consumed diet sodas: implications for urinary stone patients
Brian H. Eisner, MD1, John R. Asplin, MD2, Marshall L. Stoller, MD3.
1Massachusetts General Hospital, Boston, MA, USA, 2Litholink Corporation, Chicago, IL, USA, 3University of California, San Francisco, San Francisco, CA, USA.

BACKGROUND: Citrate is a known inhibitor of calcium stone formation. The purpose of this study was to determine the citrate and total alkali concentrations (i.e. citrate + malate) in commonly consumed diet sodas to help direct dietary recommendations for patients with nephrolithaisis.
METHODS: Citrate, and malate were measured by ion chromatography using a Dionex ICS 2000 system (Dionex Corporation, Sunnyvale, CA) equipped with an AG-11 guard column and AS-11 analytical column in series. The mobile phase was potassium hydroxide at a flow rate of 2 ml/minute. Ion peaks were detected using a conductivity meter with the eluent background conductivity suppressed using an anion self-regenerating suppressor (ASRS Ultra II, Dionex Corp). Each beverage was diluted in 0.3 M boric acid and loaded onto the column using a 25 ul sample loop.
RESULTS: The results are shown in the table below. Diet 7-up contains the greatest amount of citrate delivered as alkali (9.79 meq/l) and Diet Sunkist Orange contains the greatest amount of total alkali (8.38 meq/l of citrate + 2.11 meq/l malate = 10.49 meq/l total alkali). Several diet sodas contained greater amounts of citrate as alkali and total alkali than a lemonade formula which is commonly used to treat hypocitraturia.
CONCLUSIONS:
Several commonly consumed diet sodas contain moderate amounts of citrate and malate. This is helpful for dietary recommendations for patients with calcium nephrolithiasis and specifically those with hypocitraturia. Beverage malate content is important, as it will increase the total alkali delivered, which in turn augments citraturia.

Citrate, malate, and alkali content in commonly consumed diet sodas.
BEVERAGEpHCITRATE (mM)CITRATE AS ALKALI (mEq/l)MALATE (mM)MALATE AS ALKALI (mEq/l)TOTAL ALKALI (mEq/l)
Lemonade formula2.9115.06.3006.3
Diet Sunkist Orange3.5610.48.383.62.1110.49
Diet 7-up3.5212.59.79009.79
Diet Canada Dry3.68.36.883.42.18.98
Sierra Mist Free3.4111.38.11008.11
Fresca3.1912.37.15007.15
Diet Mountain Dew3.3110.36.78006.78
Caffeine Free Diet Coke3.250.870.54000.54
Caffeine Free Diet Pepsi3.070.230000

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