Dietary style and acid load in an Italian population of calcium kidney stone formers

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Highlights

  • A specific algorithm measures the acid load of diet as potential renal acid load (PRAL).

  • Calcium stone formers showed a lower fiber and potassium intake and a higher PRAL.

  • Dietary acid load was associated with a decrease in citrate excretion.

  • An imbalance between animal and vegetal protein intake may increase PRAL.

  • An imbalance between animal and vegetal protein intake may predispose to stones.

Abstract

Background and aims

Animal protein intake may cause an acid load that predisposes individuals to stones by influencing calcium and citrate excretion. These associations were not confirmed in recent studies. Therefore the present study was aimed to compare acid load of diet in stone formers and controls.

Methods and results

Participants to the study were 157 consecutive calcium stone formers and 144 controls. Diet was analyzed in these subjects using a software that evaluated nutrient intake from a three-day food intake diary. This software also estimated the potential renal acid load (PRAL, mEq/day). Twenty-four-hour urine excretion of ions and citrate was measured in stone formers.

Stone former diet had lower intake of glucose, fructose, potassium and fiber and higher PRAL in comparison with controls. The multinomial logistic regression analysis showed that stone risk decreased in association with the middle and the highest tertiles of fiber intake and increased in association with the highest tertile of PRAL. The linear multiple regression analysis showed that calcium excretion was associated with the sodium excretion and that citrate excretion was associated with the PRAL and animal protein intake in stone formers.

Conclusion

Our findings suggest that stone formers may undergo a greater dietary acid load sustained by a low vegetable intake and base provision. Dietary acid load does not appear as the main determinant of calcium excretion, but may promote stone risk by decreasing citrate excretion. Sodium intake may predispose to stones by stimulating calcium excretion.

Introduction

Dietary style plays an important role in kidney stone formation [1] and may explain the association of calcium nephrolithiasis with the metabolic syndrome, obesity and cardiovascular disease [2], [3]. Intake of fluids, sodium and animal proteins have been implicated in the development of calcium kidney stones [4]. Therefore, an increase in fluid intake and a reduction of sodium and animal proteins are usually recommended to patients to prevent calcium stone recurrence [5]. Animal protein intake leads to acid production, mainly through the metabolism of sulfuric acid from methionine and cysteine [4], [6]. This may predispose individuals to stones through a tubular effect that enhances calcium excretion and decreases citrate excretion, thus acting on promoters and inhibitors of calcium salt precipitation. In addition, acid load may enhance calcium excretion by stimulating calcium delivery from bones [7], [8], [9]. Despite these findings, the relationship among diet with kidney stones remains controversial. Recent epidemiological surveys confirmed the association between nephrolithiasis and the dietary acid load [10], but no association with animal protein intake [10], [11]. Furthermore, a short-term intervention study in healthy volunteers suggested that factors other than acid load explained the effect of a high-protein diet on calcium excretion [12].

Besides acid load, net acid excretion is influenced by dietary alkali content. Vegetables supply base-forming constituents that may counterbalance the acidifying effect of animal proteins [13], [14]. The possible positive effect of vegetables on stone risk was observed in association studies [11] that also observed a positive correlation between vegetable intake and citrate excretion [15].

Dietary acid load may be calculated with a previously validated algorithm including both acids and bases generated from the diet. The algorithm calculates the potential renal acid load (PRAL) from the intestinal absorption rates of ingested protein, phosphate, magnesium, potassium and calcium [16]. Meat and cheese are the main source of dietary acids and therefore significantly increase PRAL whereas other dairy products like milk and yogurt do not significantly modify PRAL and vegetable foods move it to negative values. A recent study tested this algorithm in stone formers and showed an increased dietary acid load [10].

The present study estimated PRAL in calcium stone formers to analyze the contribution of dietary acid load and animal protein intake to the stone risk. It also investigated their contribution to the excretion of calcium and citrate.

Section snippets

Methods

One hundred and fifty seven stone formers and 144 controls of Italian origin were enrolled (Table 1). Stone formers were recruited at the outpatient stone clinics of the San Raffaele or San Paolo Hospitals in Milan since 2002 to 2012. Patients had a history of urinary emission or surgical removal of calcium-oxalate or -phosphate stones or had a radiologic examination positive for radiopaque stones. Participants to the study did not take drugs affecting calcium and electrolyte metabolism.

Stone formers vs controls

Stone formers had produced the average of 4 stone in their clinical history (range 1–70). Their diet was characterized by a decreased intake of sugars, potassium and fiber in comparison with controls (Table 1). Among sugars, the intake of glucose (3.3 ± 2.45 vs 4.1 ± 2.82 mg/kcal per day, p = 0.007) and fructose (4.9 ± 3.9 vs 6.2 ± 4.67 mg/kcal per day, p = 0.012) was decreased in stone formers, whereas the intake of sucrose (11.5 ± 5.99 vs 11.9 ± 6.36 mg/kcal per day) was not different from

Discussion

The present study found that dietary acid load was increased in stone formers. Net acid load was calculated as PRAL with a standard formula that estimated bases and acids provided by diet [16]. Besides acid load, the intake of potassium, fiber, glucose and fructose was decreased in stone formers. On the contrary, animal protein intake was not different in stone formers and controls. These findings suggest that a low ingestion of vegetables and fruits, that are foods rich of bases, potassium,

Funding

This study was supported by grants from Italian Ministry of University and Research as part of a project about the prevention of kidney stones (PRIN 2005063822).

Disclosures

The authors declare no conflicts of interest.

Acknowledgment

We thank Giovanni Carpani (Blood Transfusion Centre, San Paolo Hospital, Milan, Italy) and Piera Bellinzoni (Department of Urology, San Raffaele Turro, Milan, Italy) who addressed normal subjects and patients to the study. The authors' responsibilities were as follows — GV and LS: study design, statistical analysis and manuscript preparation; ED: study design, data collection, manuscript preparation and data entry; TA, MT, LM, AM, CB, AN and FP: patient management and data collection; TM: study

References (28)

  • L. Borghi et al.

    Comparison of two diets for the prevention of recurrent stones in idiopathic hypercalciuria

    N Engl J Med

    (2002)
  • G.C. Curhan et al.

    A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones

    N Engl J Med

    (1993)
  • J. Lemann et al.

    Bone buffering of acid and base in humans

    Am J Physiol Ren Physiol

    (2003)
  • J. Calvez et al.

    Protein intake, calcium balance and health consequences

    Eur J Clin Nutr

    (2012)
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    1

    Giuseppe Vezzoli and Elena Dogliotti contributed to this work equally and share the role of the first Author.

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