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Evaluation of food intake and excretion of metabolites in nephrolithiasis

Abstracts

Introduction:

Nephrolithiasis is a common condition with high prevalence and recurrence, occuring by a complex and multifactorial process.

Objective:

To analyze the main dietary and metabolic characteristics of patients with nephrolithiasis and compare them with a control group.

Methods:

A crosssectional study with 31 patients with nephrolithiasis (NE) and 18 healthy. By the dietary intake it were observed sodium, calcium, protein, potassium, vitamin C, oxalate and water intake in both groups. Metabolic assessment were analyzed in urinary excretion of oxalate and citrate. The presence of hypertension and body mass index (BMI) was also evaluated.

Results:

In the NE group, it was found that 45.2% had a high intake of sodium and 100% a high intake of oxalate. It was also observed a low calcium, potassium and vitamin C intake by 93.5%, 100% and 94.9% respectively. Regarding protein, only 12.5% had normal protein intake. Concerning water intake, 12.9% had an ingestion less than 1 liter, 54.8% between 1 and 2 liters and 32.3% higher than 2 liters. Hypertension was observed in 64.5% of patients and adequate excretion of oxalate and citrate in 90.5% of them. There was no statistically difference in food intake, BMI and oxalate excretion between groups. However, the NE group showed higher urinary citrate.

Conclusion:

It was found in both groups a high prevalence of overweight patients, a high intake of oxalate and sodium, in addition to inadequate intakes of calcium, potassium and vitamin C. The NE group showed high protein intake and increased excretion of citrate.

citrates; calcium oxalate; nephrolithiasis; eating


Introdução:

A nefrolitíase é uma patologia frequente, com alta taxa de prevalência e recorrência, ocorrendo por processo multifatorial e complexo.

Objetivo:

Analisar as principais características dietéticas e metabólicas de pacientes com nefrolitíase e compará-los com grupo controle.

Métodos:

Estudo observacional, transversal, com 31 pacientes com nefrolitíase (NE) e 18 saudáveis. Na ingestão dietética, foram verificados sódio, cálcio, proteína, potássio, vitamina C, oxalato e a ingestão hídrica em ambos os grupos. Na avaliação metabólica, foi analisada excreção urinária de citrato e oxalato. Também foi avaliada presença de hipertensão arterial e Índice de Massa Corporal (IMC).

Resultados:

Quanto ao grupo NE, verificou-se que 45,2% apresentou alta ingestão de sódio e 100% de oxalato. Foi também observada baixa ingestão de cálcio em 93,5%, potássio em 100% e vitamina C em 94,9%. Com relação à proteína, apenas 12,5% apresentou ingestão normoproteica. Quanto à ingestão hídrica, 12,9% apresentou ingestão menor que 1 litro, 54,8% entre 1 a 2 litros, e 32,3% maior que 2 litros. Foi observada hipertensão arterial sistêmica em 64,5% desses pacientes e excreção adequada de citrato e oxalato em 90,5% deles. Não foi verificada diferença estatística significativa na ingestão alimentar, IMC, e excreção de oxalato entre os grupos. No entanto, o grupo NE apresentou maior excreção de citrato.

Conclusão:

Verificou-se nos dois grupos elevada prevalência de pacientes com sobrepeso, alta ingestão de oxalato e sódio, além de inadequação nas ingestões de cálcio, potássio e vitamina C. No grupo NE, foi observada alta ingestão proteica e maior excreção de citrato.

citratos; ingestão de alimentos; nefrolitíase; oxalato de cálcio


Introduction

Nephrolithiasis - a chronic disease1Sakhaee K. Pharmacology of stone disease. Adv Chronic Kidney Dis 2009;16:30-8. DOI: http://dx.doi.org/10.1053/j.ackd.2008.10.004
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that affects between 5% and 15% of the world's population2Peres LAB, Almeida LP, Bolson LB, Brites MF, David JM, Tazima L. Investigação de nefrolitíase no Oeste do Paraná. J Bras Nefrol 2011;33:160-5. DOI: http://dx.doi.org/10.1590/S0101-28002011000200007
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Ferraz FHRP, Carvalho PRA, Souza RR. Perfil dos pacientes portadores de nefrolitíase em tratamento ambulatorial em um hospital público do Distrito Federal. Brasília Med 2011;48:252-7.
- 4Souza PT, Deus RB, Malagutti W, Silva RN, Rodrigues FSM, Ferraz RRN. Prevalência de sinais sugestivos de litíase urinária em trabalhadores do serviço de teleatendimento. ConScientiae Saúde 2009;8:641-7. - is considered a public health problem.3Ferraz FHRP, Carvalho PRA, Souza RR. Perfil dos pacientes portadores de nefrolitíase em tratamento ambulatorial em um hospital público do Distrito Federal. Brasília Med 2011;48:252-7. Renal lithiasis occurs in young adults5Pearle MS. Prevention of nephrolithiasis. Curr Opin Nephrol Hypertens 2001;10:203-9. DOI: http://dx.doi.org/10.1097/00041552-200103000-00008
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Wilkinson H. Clinical investigation and management of patients with renal stones. Ann Clin Biochem 2001;38:180-7. PMID: 11392494 DOI: http://dx.doi.org/10.1258/0004563011900623
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- 7Sociedade Brasileira de Nefrologia. Diretrizes de litíase urinária. J Bras Nefrol 2002;24:203-7. and males in particular.2Peres LAB, Almeida LP, Bolson LB, Brites MF, David JM, Tazima L. Investigação de nefrolitíase no Oeste do Paraná. J Bras Nefrol 2011;33:160-5. DOI: http://dx.doi.org/10.1590/S0101-28002011000200007
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, 7Sociedade Brasileira de Nefrologia. Diretrizes de litíase urinária. J Bras Nefrol 2002;24:203-7. Incidence peaks in the third and fourth decades of life,5Pearle MS. Prevention of nephrolithiasis. Curr Opin Nephrol Hypertens 2001;10:203-9. DOI: http://dx.doi.org/10.1097/00041552-200103000-00008
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Wilkinson H. Clinical investigation and management of patients with renal stones. Ann Clin Biochem 2001;38:180-7. PMID: 11392494 DOI: http://dx.doi.org/10.1258/0004563011900623
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- 7Sociedade Brasileira de Nefrologia. Diretrizes de litíase urinária. J Bras Nefrol 2002;24:203-7. although children are frequently affected.2Peres LAB, Almeida LP, Bolson LB, Brites MF, David JM, Tazima L. Investigação de nefrolitíase no Oeste do Paraná. J Bras Nefrol 2011;33:160-5. DOI: http://dx.doi.org/10.1590/S0101-28002011000200007
http://dx.doi.org/10.1590/S0101-28002011...
Approximately 50% of the untreated patients suffer from recurring kidney stones within a period of five years.8Gomes PN. Profilaxia da litíase renal. Acta Urol 2005;22;3:47-56.

Renal lithiasis ranks third among the diseases of the genitourinary system, after urinary infection and diseases of the prostate. Calcium kidney stones are present in 85% of the cases of renal lithiasis. They form due to increases in the levels of urine oxalate, calcium, and uric acid, or decreases in urinary citrate levels.8Gomes PN. Profilaxia da litíase renal. Acta Urol 2005;22;3:47-56.

Most renal calculi have a mixed composition, consisting of approximately 30% of monominerals.8Gomes PN. Profilaxia da litíase renal. Acta Urol 2005;22;3:47-56. One of the most common minerals is calcium oxalate,8Gomes PN. Profilaxia da litíase renal. Acta Urol 2005;22;3:47-56. , 9Taylor EM, Curhan GC. Oxalate intake and the risk for nephrolithiasis. J Am Soc Nephrol 2007;18:2198-204. DOI: http://dx.doi.org/10.1681/ASN.2007020219
http://dx.doi.org/10.1681/ASN.2007020219...
40% to 50% of which is excreted in the urine after being consumed as part of one's diet.1010 Sociedade Brasileira de Urologia. Litíase urinária: aspectos metabológicos em adultos e crianças; 2006. Oxalate can be found in vegetable species, which inevitably makes it an element in human diet. It is present in seeds, including cereals, spinach and some roots. Beets are particularly rich in oxalate.1111 Holmes RP, Goodman HO, Assimos DG. Contribution of dietary oxalate to urinary oxalate excretion. Kidney Int 2001;59:270-6. PMID: 11135080 DOI: http://dx.doi.org/10.1046/j.1523-1755.2001.00488.x
http://dx.doi.org/10.1046/j.1523-1755.20...

Stones form in a complex multi-factorial process. Some of the factors associated with calculi formation are the climate,7Sociedade Brasileira de Nefrologia. Diretrizes de litíase urinária. J Bras Nefrol 2002;24:203-7. , 8Gomes PN. Profilaxia da litíase renal. Acta Urol 2005;22;3:47-56. one's occupation,8Gomes PN. Profilaxia da litíase renal. Acta Urol 2005;22;3:47-56. , 1010 Sociedade Brasileira de Urologia. Litíase urinária: aspectos metabológicos em adultos e crianças; 2006. nutrition,8Gomes PN. Profilaxia da litíase renal. Acta Urol 2005;22;3:47-56. , 7Sociedade Brasileira de Nefrologia. Diretrizes de litíase urinária. J Bras Nefrol 2002;24:203-7. age,2Peres LAB, Almeida LP, Bolson LB, Brites MF, David JM, Tazima L. Investigação de nefrolitíase no Oeste do Paraná. J Bras Nefrol 2011;33:160-5. DOI: http://dx.doi.org/10.1590/S0101-28002011000200007
http://dx.doi.org/10.1590/S0101-28002011...
, 8Gomes PN. Profilaxia da litíase renal. Acta Urol 2005;22;3:47-56. gender,2Peres LAB, Almeida LP, Bolson LB, Brites MF, David JM, Tazima L. Investigação de nefrolitíase no Oeste do Paraná. J Bras Nefrol 2011;33:160-5. DOI: http://dx.doi.org/10.1590/S0101-28002011000200007
http://dx.doi.org/10.1590/S0101-28002011...
, 8Gomes PN. Profilaxia da litíase renal. Acta Urol 2005;22;3:47-56. , 1010 Sociedade Brasileira de Urologia. Litíase urinária: aspectos metabológicos em adultos e crianças; 2006. genetics,7Sociedade Brasileira de Nefrologia. Diretrizes de litíase urinária. J Bras Nefrol 2002;24:203-7. , 8Gomes PN. Profilaxia da litíase renal. Acta Urol 2005;22;3:47-56. and metabolic disorders.8Gomes PN. Profilaxia da litíase renal. Acta Urol 2005;22;3:47-56. , 1010 Sociedade Brasileira de Urologia. Litíase urinária: aspectos metabológicos em adultos e crianças; 2006.

Urinary supersaturation - considered to be the initiating event in stone formation4Souza PT, Deus RB, Malagutti W, Silva RN, Rodrigues FSM, Ferraz RRN. Prevalência de sinais sugestivos de litíase urinária em trabalhadores do serviço de teleatendimento. ConScientiae Saúde 2009;8:641-7. , 1212 Carvalho M, Ferrari ACH, Renner LO, Vieira MA, Riella MC. Quantificação do Stone Clinic Effect em pacientes com nefrolitíase. Rev Assoc Med Bras 2004;50:79-82. DOI: http://dx.doi.org/10.1590/S0104-42302004000100040
http://dx.doi.org/10.1590/S0104-42302004...
- may result from three main alterations: high levels of substances known to promote stone formation, low levels of substances known to inhibit crystallization,4Souza PT, Deus RB, Malagutti W, Silva RN, Rodrigues FSM, Ferraz RRN. Prevalência de sinais sugestivos de litíase urinária em trabalhadores do serviço de teleatendimento. ConScientiae Saúde 2009;8:641-7. , 8Gomes PN. Profilaxia da litíase renal. Acta Urol 2005;22;3:47-56. and decreased urine volume.4Souza PT, Deus RB, Malagutti W, Silva RN, Rodrigues FSM, Ferraz RRN. Prevalência de sinais sugestivos de litíase urinária em trabalhadores do serviço de teleatendimento. ConScientiae Saúde 2009;8:641-7. Abnormal crystalluria then occurs, along with crystal nucleation, growth and aggregation, thereby developing the grounds for the establishment of nephrolithiasis.8Gomes PN. Profilaxia da litíase renal. Acta Urol 2005;22;3:47-56.

Studies have indicated the existence of an association between dietary factors,9Taylor EM, Curhan GC. Oxalate intake and the risk for nephrolithiasis. J Am Soc Nephrol 2007;18:2198-204. DOI: http://dx.doi.org/10.1681/ASN.2007020219
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, 1313 Silver J, Rubinger D, Friedlaender MM, Popovtzer MM. Sodium-dependent idiopathic hypercalciuria in renal-stone formers. Lancet 1983;2:484-6. DOI: http://dx.doi.org/10.1016/S0140-6736(83)90513-5
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, 1414 Curhan GC, Willett WC, Rimm EB, Stampfer MJ. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med 1993;328:833-8. PMID: 8441427 DOI: http://dx.doi.org/10.1056/NEJM199303253281203
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systemic hypertension,4Souza PT, Deus RB, Malagutti W, Silva RN, Rodrigues FSM, Ferraz RRN. Prevalência de sinais sugestivos de litíase urinária em trabalhadores do serviço de teleatendimento. ConScientiae Saúde 2009;8:641-7. , 1515 Borghi L, Meschi T, Guerra A, Briganti A, Schianchi T, Allegri F, et al. Essential arterial hypertension and stone disease. Kidney Int 1999;55:2397-406. PMID: 10354288 DOI: http://dx.doi.org/10.1046/j.1523-1755.1999.00483.x
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body weight,2Peres LAB, Almeida LP, Bolson LB, Brites MF, David JM, Tazima L. Investigação de nefrolitíase no Oeste do Paraná. J Bras Nefrol 2011;33:160-5. DOI: http://dx.doi.org/10.1590/S0101-28002011000200007
http://dx.doi.org/10.1590/S0101-28002011...
, 1515 Borghi L, Meschi T, Guerra A, Briganti A, Schianchi T, Allegri F, et al. Essential arterial hypertension and stone disease. Kidney Int 1999;55:2397-406. PMID: 10354288 DOI: http://dx.doi.org/10.1046/j.1523-1755.1999.00483.x
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, 1616 Taylor EN, Stampfer MJ, Curhan GC. Obesity, weight gain, and the risk of kidney stones. JAMA 2005;293:455-62. PMID: 15671430 DOI: http://dx.doi.org/10.1001/jama.293.4.455
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and metabolite excretion9Taylor EM, Curhan GC. Oxalate intake and the risk for nephrolithiasis. J Am Soc Nephrol 2007;18:2198-204. DOI: http://dx.doi.org/10.1681/ASN.2007020219
http://dx.doi.org/10.1681/ASN.2007020219...
, 1414 Curhan GC, Willett WC, Rimm EB, Stampfer MJ. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med 1993;328:833-8. PMID: 8441427 DOI: http://dx.doi.org/10.1056/NEJM199303253281203
http://dx.doi.org/10.1056/NEJM1993032532...
, 1717 Taylor EN, Stampfer MJ, Curhan GC. Dietary factors and the risk of incident kidney stones in men: new insights after 14 years of follow-up. J Am Soc Nephrol 2004;15:3225-32. DOI: http://dx.doi.org/10.1097/01.ASN.0000146012.44570.20
http://dx.doi.org/10.1097/01.ASN.0000146...
with the stone formation process, in addition to stressing the need to carry out in-depth investigations on the topic in order to identify and correct the imbalances that cause renal lithiasis.

This study aimed to describe and compare the nutritional, dietary, and metabolic profiles of subjects with and without nephrolithiasis.

Methods

This observational cross-sectional study enrolled healthy controls and patients from the Nephrology Outpatient Clinic at the Hospital de Clinicas of the Federal University of Paraná. The individuals with nephrolithiasis had to meet at least one of the following enrollment criteria: renal colic with confirmed hematuria, radiological evidence of nephrolithiasis, or history of spontaneous expulsion or surgical removal of kidney stones. Patients with recurrent nephrolithiasis had to have had more than two calculi with radiological confirmation and had to have been seen at least twice in the clinic. Additionally, enrolled patients could not have been advised by a nutritionist prior to the start of the study. Participants had to be 18 years or older to join the study and be able to understand and sign the informed consent form. Individuals with calcium metabolism disorders such as primary hyperparathyroidism, medullary sponge kidney, renal tubular acidosis, malignant disease, and decreased renal function (creatinine clearance of less than 70 ml/min) were excluded. The study was approved by the Ethics Committee for Research with Humans of the Hospital de Clinicas, Federal University of Paraná.

The biochemical analyses and ensuing data on metabolism related to the excretion of urinary oxalate and citrate were obtained from 24-hour urine tests. Laboratory tests were deemed satisfactory when the minimum reference value for citrate excretion was 320 mg/24h;1818 Cunha MA, Schor N. Valores de referência de parâmetros urinários envolvidos na litogênese. J Bras Nefrol 1996;18:124-9. for excreted oxalate, the maximum reference value was 45 mg/day.1919 Milliner DS. Urolithiasis. In: Avner ED, Harmon WE, Niaudet P, Yoshikawa N, eds. Pediatric Nephrology. 6th ed. Boston: Springer; 2009. p.1405-30. Patients previously diagnosed with or on drugs for systemic hypertension (SH) were considered hypertensive.

The nutritional assessment of enrolled patients included an interview and anthropometric measurements. The interview covered the identification of the subjects and factors related to food and fluid intake.

The assessment of oxalate dietary intake of the groups was based on a semi-quantitative Food Frequency Questionnaire (FFQ).2020 Ribeiro AC, Sávio KEO, Rodrigues MLCF, Costa THC, Schmitz BAS. Validação de um questionário de freqüência de consumo alimentar para população adulta. Rev Nutr 2006;19:553-62. DOI: http://dx.doi.org/10.1590/S1415-52732006000500003
http://dx.doi.org/10.1590/S1415-52732006...
The FFQ looked into the monthly frequency with which individuals ate from a wide range of food groups. Patients were asked to fill in a 24-hour dietary recall2121 Karvetti RL, Knuts LR. Validity of the 24-hour dietary recall. J Am Diet Assoc 1985;85:1437-42. in addition to the FFQ to have the intake of other nutrients estimated. Online software Avanutri® was used to analyze the data gathered from the patient 24-hour dietary recalls.

The intake of micronutrients - minus oxalate - was verified for adequacy against the reference values of the Recommended Dietary Allowances (RDA) present in the Dietary Reference Intakes (DRI)2222 Food and nutrition board. National Research Council. Institute of Medicine. Dietary reference intakes: applications in dietary assessment. Washington: National Academy Press; 2000. for each age range and gender. Values for vitamin C, calcium, potassium, and phosphorous were considered adequate when they were equal to or higher than the values in the RDA. Oxalate intake was estimated from the responses to the FFQ. Each food item mentioned in the FFQ had its oxalate content calculated2323 Hsph.harvard.edu. Boston: Harvard School of public health. [Internet] [Acesso 20 nov 2013]. Disponível em: https://regepi.bwh.harvard.edu/health/Oxalate/files
https://regepi.bwh.harvard.edu/health/Ox...
based on the quantities in household weights and measures and the frequency with which the patients reported to eat these foods. The oxalate contents of the food items were added together to yield the total habitual intake of oxalate. Total oxalate intake was then divided by 30 days to yield the mean daily oxalate intake. Oxalate intakes of less than 55 mg/day2424 Massey LK, Palmer RG, Horner HT. Oxalate content of soybean seeds (Glycine max: Leguminosae), soyfoods, and other edible legumes. J Agric Food Chem 2001;49:4262-6. PMID: 11559120 DOI: http://dx.doi.org/10.1021/jf010484y
http://dx.doi.org/10.1021/jf010484y...
were deemed adequate.

Adequate intake of sodium was limited to a maximum of 2000 mg/day, as defined by the World Health Organization.2525 World Health Organization. Guideline: sodium intake for adults and children. Geneva: World Health Organization; 2012. Amounts exceeding this threshold were considered inadequate. A nutritional composition software program was used in the evaluation of sodium intake to consider food-intrinsic sodium levels and the sodium present in the salt added to the food. However, added sodium cannot be assessed based on the consumption patterns of the Brazilian population, since the software already accounts for the added salt - and therefore the sodium - in certain preparations.

Necessary protein intake levels were estimated according to Martin & Cardoso.2626 Martins C, Cardoso SP. Terapia nutricional enteral e parenteral. Manual de rotina técnica. Curitiba: Nutroclínica; 2000. p.23-55. Individuals with normal protein levels in their diets ate 1 to 1.2 g of protein per kilogram of body weight per day. As for fluid intake, patients were asked about how much water and other fluids they had.

In the anthropometric assessment carried out after the interview, enrolled individuals were weighed and measured for their heights. Subjects were asked to wear as little clothing as possible while they were weighed on a portable scale with 150 kg capacity and 100 g readability. The anthropometer in the scale was used for height measurements. Patients were asked to remove their shoes and accessories on their hair and heads, stand up straight in the center of the equipment with arms alongside their bodies and heads up, looking at a fixed point at eye level. Heights and weights were used to calculate the Body Mass Index (BMI) and categorize the subjects according to the criteria of the World Health Organization.2727 World Health Organization. Obesity: preventing and managing the global epidemic. Report of a World Health Organization Consultation. Geneva: World Health Organization; 2000. p.256.

The statistical analysis of nutritional and urinary biochemical parameters was performed on software package SPSS version 17.0 for Windows® (SPSS, Chicago, IL) to allow for further comparisons.

Numerical variables were compared through Student's t-test and the Mann-Whitney U test, the latter being used to treat nonparametric data. The chi-square (χ2) test, Fisher's exact test and the Mann-Whitney U test were used to compare between categorical variables. When the assumptions for application of the χ2 test were not present, the Mann-Whitney U test was used to check for differences between groups according to rank sum. Fisher's exact test was used for dichotomous variables. The significance level was set at 0.05.

Results

Thirty-one of the 49 enrolled subjects were in the nephrolithiasis (NL) group and 18 in the control group. In the NL group, 16.67% of the individuals were males, versus 25.81% in the control. The two groups were not statistically different in this respect (Fisher's exact test; p = 0.322).

The assessment of age, BMI, and dietary categorization included the data from 31 patients in the NL group and 18 in the control group. Citrate and oxalate excretion analysis included the information of 21 patients in the NL group and nine in the control group.

Mean age, mean BMI and oxalate excretion were not statistically different between groups. However, citrate excretion was significantly higher in the NL group (p = 0.039), as seen in Table 1.

Table 1
Characterization of enrolled subjects - groups

No statistical difference (chi-square; p = 0.579) was seen between groups in terms of hypertension, as 64.5% of the subjects in the NL group and 72.2% of the controls were hypertensive. BMI calculations revealed that 12.9% of the individuals with nephrolithiasis had normal weight, 51.6% were overweight, and 35.5% obese. In the control group, 11.1% had normal weight, 33.3% were overweight, and 55.6% obese. There was no statistical difference between groups (p = 0.236).

No statistically significant differences were seen in the intake of sodium, calcium, potassium, vitamin C, oxalate, and protein (Table 2).

Table 2
Mean micronutrient and oxalate intake in the nl and control groups

When micronutrient intake and oxalate levels were analyzed, only half of the individuals in the NL group were found to have ideal levels of sodium intake. Inadequate levels of calcium intake were observed in 93.50% of the patients in the NL group. The same was true for 100% of the individuals in this group for potassium and 83.90% for vitamin C. Most of the individuals enrolled in the study had oxalate intake above recommended levels (Table 3). In terms of metabolite excretion, a greater number of individuals in the NL group had adequate levels of citrate excretion. Although no significant differences were found between groups for oxalate excretion (p = 0.367), most of the individuals in the NL group had adequate levels of oxalate excretion (Table 3).

Table 3
Percent adequate intake and excretion of micronutrients and urinary metabolites

No statistically significant differences were observed in protein intake between groups (Mann-Whitney, p = 0.313). A third (33.3%) of the subjects in the NL group were on hypoproteic diets, 12.5% had normal protein intake levels, and 54.2% were on hyperproteic diets. In the control group, 55.6% of the subjects were on hypoproteic diets, 11.1% had normal protein intake levels, and 33.3% were on hyperproteic diets.

Water intake data revealed that 12.90% of the subjects in the NL group drank less than one liter of water, 54.80% had between one and two liters, and 32.30% had more than two liters of water per day. In the control group, 22.20% had less than a liter of water, 44.40% had between one and two liters, and 33.30% had more than two liters of water per day. No statistically significant differences were seen in the water intake level of the two groups (Chi-square; p = 0.335).

Discussion

Nutritional care should focus on reducing the incidence and recurrence of nephrolithiasis.4Souza PT, Deus RB, Malagutti W, Silva RN, Rodrigues FSM, Ferraz RRN. Prevalência de sinais sugestivos de litíase urinária em trabalhadores do serviço de teleatendimento. ConScientiae Saúde 2009;8:641-7. Studies have shown that dietary treatments can effectively reduce the formation of kidney stones.9Taylor EM, Curhan GC. Oxalate intake and the risk for nephrolithiasis. J Am Soc Nephrol 2007;18:2198-204. DOI: http://dx.doi.org/10.1681/ASN.2007020219
http://dx.doi.org/10.1681/ASN.2007020219...
, 1212 Carvalho M, Ferrari ACH, Renner LO, Vieira MA, Riella MC. Quantificação do Stone Clinic Effect em pacientes com nefrolitíase. Rev Assoc Med Bras 2004;50:79-82. DOI: http://dx.doi.org/10.1590/S0104-42302004000100040
http://dx.doi.org/10.1590/S0104-42302004...
, 2828 Borghi L, Schianchi T, Meschi T, Guerra A, Allegri F, Maggiore U, et al. Comparison of two diets for the prevention of recurrent stones in idiopathic hypercalciuria. N Engl J Med 2002;346:77-84. PMID: 11784873 DOI: http://dx.doi.org/10.1056/NEJMoa010369
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, 2929 Voss S, Hesse A, Zimmermann DJ, Sauerbruch T, von Unruh GE. Intestinal oxalate absorption is higher in idiopathic calcium oxalate stone formers than in healthy controls: measurements with the [(13)C2]oxalate absorption test. J Urol 2006;175:1711-5. DOI: http://dx.doi.org/10.1016/S0022-5347(05)01001-3
http://dx.doi.org/10.1016/S0022-5347(05)...
Individuals should also be examined for their metabolic status, in order to allow for the economical and efficient identification and correction of substance imbalances that may impact the stone formation process.8Gomes PN. Profilaxia da litíase renal. Acta Urol 2005;22;3:47-56.

Nephrolithiasis has been associated with systemic hypertension.2Peres LAB, Almeida LP, Bolson LB, Brites MF, David JM, Tazima L. Investigação de nefrolitíase no Oeste do Paraná. J Bras Nefrol 2011;33:160-5. DOI: http://dx.doi.org/10.1590/S0101-28002011000200007
http://dx.doi.org/10.1590/S0101-28002011...
In our study, no significant differences were seen between patients with lithiasis and healthy controls in this respect. However, 64.5% of the individuals in the NL group were hypertensive. Ferraz et al.3Ferraz FHRP, Carvalho PRA, Souza RR. Perfil dos pacientes portadores de nefrolitíase em tratamento ambulatorial em um hospital público do Distrito Federal. Brasília Med 2011;48:252-7. reported that 19.3% of the patients with nephrolithiasis had SH. Other authors have found that hypertensive patients had higher urinary excretion of calcium and oxalate,4Souza PT, Deus RB, Malagutti W, Silva RN, Rodrigues FSM, Ferraz RRN. Prevalência de sinais sugestivos de litíase urinária em trabalhadores do serviço de teleatendimento. ConScientiae Saúde 2009;8:641-7. , 1515 Borghi L, Meschi T, Guerra A, Briganti A, Schianchi T, Allegri F, et al. Essential arterial hypertension and stone disease. Kidney Int 1999;55:2397-406. PMID: 10354288 DOI: http://dx.doi.org/10.1046/j.1523-1755.1999.00483.x
http://dx.doi.org/10.1046/j.1523-1755.19...
occasionally accompanied by higher incidences of hypocitraturia.3030 Taylor EN, Mount DB, Forman JP, Curhan GC. Association of prevalent hypertension with 24-hour urinary excretion of calcium, citrate, and other factors. Am J Kidney Dis 2006;47:780-9. PMID: 16632016 DOI: http://dx.doi.org/10.1053/j.ajkd.2006.01.024
http://dx.doi.org/10.1053/j.ajkd.2006.01...
However, Taylor et al.3030 Taylor EN, Mount DB, Forman JP, Curhan GC. Association of prevalent hypertension with 24-hour urinary excretion of calcium, citrate, and other factors. Am J Kidney Dis 2006;47:780-9. PMID: 16632016 DOI: http://dx.doi.org/10.1053/j.ajkd.2006.01.024
http://dx.doi.org/10.1053/j.ajkd.2006.01...
failed to find an association between urinary calcium excretion and hypertension. There is indication that history of nephrolithiasis may be associated with increased risk of developing hypertension.3131 Strazzullo P, Barba G, Vuotto P, Farinaro E, Siani A, Nunziata V, et al. Past history of nephrolithiasis and incidence of hypertension in men: a reappraisal based on the results of the Olivetti Prospective Heart Study. Nephrol Dial Transplant 2001;16:2232-5. DOI: http://dx.doi.org/10.1093/ndt/16.11.2232
http://dx.doi.org/10.1093/ndt/16.11.2232...

Nephrolithiasis has been associated with obesity.2Peres LAB, Almeida LP, Bolson LB, Brites MF, David JM, Tazima L. Investigação de nefrolitíase no Oeste do Paraná. J Bras Nefrol 2011;33:160-5. DOI: http://dx.doi.org/10.1590/S0101-28002011000200007
http://dx.doi.org/10.1590/S0101-28002011...
Although no significant BMI differences were seen between groups, 87.1% of the subjects in the NL group were overweight. Several studies have observed an association between a high BMI and formation of kidney stones.2Peres LAB, Almeida LP, Bolson LB, Brites MF, David JM, Tazima L. Investigação de nefrolitíase no Oeste do Paraná. J Bras Nefrol 2011;33:160-5. DOI: http://dx.doi.org/10.1590/S0101-28002011000200007
http://dx.doi.org/10.1590/S0101-28002011...
, 1515 Borghi L, Meschi T, Guerra A, Briganti A, Schianchi T, Allegri F, et al. Essential arterial hypertension and stone disease. Kidney Int 1999;55:2397-406. PMID: 10354288 DOI: http://dx.doi.org/10.1046/j.1523-1755.1999.00483.x
http://dx.doi.org/10.1046/j.1523-1755.19...
, 1616 Taylor EN, Stampfer MJ, Curhan GC. Obesity, weight gain, and the risk of kidney stones. JAMA 2005;293:455-62. PMID: 15671430 DOI: http://dx.doi.org/10.1001/jama.293.4.455
http://dx.doi.org/10.1001/jama.293.4.455...
Powell et al.3232 Powell CR, Stoller ML, Schwartz BF, Kane C, Gentle DL, Bruce JE, et al. Impact of body weight on urinary electrolytes in urinary stone formers. Urology 2000;55:825-30. PMID: 10840085 DOI: http://dx.doi.org/10.1016/S0090-4295(99)00617-2
http://dx.doi.org/10.1016/S0090-4295(99)...
reported that obesity alone does not increase the risk of recurrence of kidney stones. Nevertheless, individuals with a high BMI are more prone to having urinary crystallization.4Souza PT, Deus RB, Malagutti W, Silva RN, Rodrigues FSM, Ferraz RRN. Prevalência de sinais sugestivos de litíase urinária em trabalhadores do serviço de teleatendimento. ConScientiae Saúde 2009;8:641-7. Some of the main metabolic disorders seen in obese individuals are hypercalciuria, hyperoxaluria, and hyperuricosuria.4Souza PT, Deus RB, Malagutti W, Silva RN, Rodrigues FSM, Ferraz RRN. Prevalência de sinais sugestivos de litíase urinária em trabalhadores do serviço de teleatendimento. ConScientiae Saúde 2009;8:641-7. Powell et al.3232 Powell CR, Stoller ML, Schwartz BF, Kane C, Gentle DL, Bruce JE, et al. Impact of body weight on urinary electrolytes in urinary stone formers. Urology 2000;55:825-30. PMID: 10840085 DOI: http://dx.doi.org/10.1016/S0090-4295(99)00617-2
http://dx.doi.org/10.1016/S0090-4295(99)...
divided obese and non-obese male patients with nephrolithiasis into groups and noted that obese subjects had higher levels of urinary oxalate excretion. No differences were seen between groups in terms of citrate excretion. The authors concluded that generally, despite the differences, the frequency of recurrent kidney stones in obese and non-obese subjects was similar. The authors also looked at obese and non-obese females with nephrolithiasis and found that obese women had a slightly greater number of episodes of kidney stones than non-obese women suffering from nephrolithiasis. Souza et al.4Souza PT, Deus RB, Malagutti W, Silva RN, Rodrigues FSM, Ferraz RRN. Prevalência de sinais sugestivos de litíase urinária em trabalhadores do serviço de teleatendimento. ConScientiae Saúde 2009;8:641-7. reported that half of their patients with nephrolithiasis had a high BMI and low levels of water intake.

In our study, no statistically significant differences were seen between groups in terms of sodium intake levels. However, most of the individuals in the NL group (45.2%) had sodium intake above recommended levels. Yet, sodium intake may have been underestimated, since the salt added by the patients was not considered in this study. For example, the 2008-2009 Household Budget Survey (POF 2008-2009)3333 Brasil. Fundação IBGE. Pesquisa de orçamento familiar-2008/2009. Análise do consumo alimentar pessoal no Brasil. Rio de Janeiro; 2011. indicated that the daily sodium intake of Brazilian males and females within the same age groups as the population described in our study ranged from 3637.6 mg to 3186.5 mg, and from 2809.3 mg to 2608.0 mg, respectively.

Some studies have suggested that high levels of sodium intake may increase the risk of hypercalciuria,7Sociedade Brasileira de Nefrologia. Diretrizes de litíase urinária. J Bras Nefrol 2002;24:203-7. , 1313 Silver J, Rubinger D, Friedlaender MM, Popovtzer MM. Sodium-dependent idiopathic hypercalciuria in renal-stone formers. Lancet 1983;2:484-6. DOI: http://dx.doi.org/10.1016/S0140-6736(83)90513-5
http://dx.doi.org/10.1016/S0140-6736(83)...
, 1515 Borghi L, Meschi T, Guerra A, Briganti A, Schianchi T, Allegri F, et al. Essential arterial hypertension and stone disease. Kidney Int 1999;55:2397-406. PMID: 10354288 DOI: http://dx.doi.org/10.1046/j.1523-1755.1999.00483.x
http://dx.doi.org/10.1046/j.1523-1755.19...
and that sodium restriction may benefit individuals with idiopathic hypercalciuria.1313 Silver J, Rubinger D, Friedlaender MM, Popovtzer MM. Sodium-dependent idiopathic hypercalciuria in renal-stone formers. Lancet 1983;2:484-6. DOI: http://dx.doi.org/10.1016/S0140-6736(83)90513-5
http://dx.doi.org/10.1016/S0140-6736(83)...
Sodium has also been thought to reduce citrate excretion.7Sociedade Brasileira de Nefrologia. Diretrizes de litíase urinária. J Bras Nefrol 2002;24:203-7. However, another study found no association between sodium intake and increased risk of renal lithiasis.3434 Curhan GC, Willett WC, Knight EL, Stampfer MJ. Dietary factors and the risk of incident kidney stones in younger women: Nurses' Health Study II. Arch Intern Med 2004;164:885-91. PMID: 15111375 DOI: http://dx.doi.org/10.1001/archinte.164.8.885
http://dx.doi.org/10.1001/archinte.164.8...
Sodium chloride intake by hypertensive subjects deserves consideration, as it maintains blood pressure at high levels and induces increased excretion of calcium.1515 Borghi L, Meschi T, Guerra A, Briganti A, Schianchi T, Allegri F, et al. Essential arterial hypertension and stone disease. Kidney Int 1999;55:2397-406. PMID: 10354288 DOI: http://dx.doi.org/10.1046/j.1523-1755.1999.00483.x
http://dx.doi.org/10.1046/j.1523-1755.19...

No significant differences were observed between groups for calcium intake; however, 93.5% of the subjects in the NL group had less calcium than recommended for their gender and age. The association between calcium intake and formation of kidney stones is probably related to calcium forming a complex with oxalate in the bowel, thereby lower calcium intake causes increased absorption of oxalate1010 Sociedade Brasileira de Urologia. Litíase urinária: aspectos metabológicos em adultos e crianças; 2006. , 1414 Curhan GC, Willett WC, Rimm EB, Stampfer MJ. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med 1993;328:833-8. PMID: 8441427 DOI: http://dx.doi.org/10.1056/NEJM199303253281203
http://dx.doi.org/10.1056/NEJM1993032532...
, 3434 Curhan GC, Willett WC, Knight EL, Stampfer MJ. Dietary factors and the risk of incident kidney stones in younger women: Nurses' Health Study II. Arch Intern Med 2004;164:885-91. PMID: 15111375 DOI: http://dx.doi.org/10.1001/archinte.164.8.885
http://dx.doi.org/10.1001/archinte.164.8...
, 3535 Curhan GC, Willett WC, Speizer FE, Stampfer MJ. Twenty-four-hour urine chemistries and the risk of kidney stones among women and men. Kidney Int 2001;59:2290-8. PMID: 11380833 and compromises bone mineral density.1010 Sociedade Brasileira de Urologia. Litíase urinária: aspectos metabológicos em adultos e crianças; 2006. Given that most kidney stones have calcium in them and that hypercalciuria has been associated with the formation of renal calculi, calcium restriction has been adopted as a recommendation for patients with renal lithiasis.1414 Curhan GC, Willett WC, Rimm EB, Stampfer MJ. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med 1993;328:833-8. PMID: 8441427 DOI: http://dx.doi.org/10.1056/NEJM199303253281203
http://dx.doi.org/10.1056/NEJM1993032532...
Curhan et al.1414 Curhan GC, Willett WC, Rimm EB, Stampfer MJ. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med 1993;328:833-8. PMID: 8441427 DOI: http://dx.doi.org/10.1056/NEJM199303253281203
http://dx.doi.org/10.1056/NEJM1993032532...
assessed the diets of approximately 45,000 men for a period of 4-5 years, and found that the group with higher calcium intake levels (more than 1050 mg/day) had a significantly lower risk of developing kidney stones versus the group having less than 605 mg/day of calcium. Borghi et al.2828 Borghi L, Schianchi T, Meschi T, Guerra A, Allegri F, Maggiore U, et al. Comparison of two diets for the prevention of recurrent stones in idiopathic hypercalciuria. N Engl J Med 2002;346:77-84. PMID: 11784873 DOI: http://dx.doi.org/10.1056/NEJMoa010369
http://dx.doi.org/10.1056/NEJMoa010369...
reported that decreases in calcium intake reduce urinary calcium excretion and may cause increased urinary oxalate excretion, which by its turn increases the risk of subjects developing nephrolithiasis. While some studies have indicated increased risk of nephrolithiasis in low calcium diets,9Taylor EM, Curhan GC. Oxalate intake and the risk for nephrolithiasis. J Am Soc Nephrol 2007;18:2198-204. DOI: http://dx.doi.org/10.1681/ASN.2007020219
http://dx.doi.org/10.1681/ASN.2007020219...
, 2929 Voss S, Hesse A, Zimmermann DJ, Sauerbruch T, von Unruh GE. Intestinal oxalate absorption is higher in idiopathic calcium oxalate stone formers than in healthy controls: measurements with the [(13)C2]oxalate absorption test. J Urol 2006;175:1711-5. DOI: http://dx.doi.org/10.1016/S0022-5347(05)01001-3
http://dx.doi.org/10.1016/S0022-5347(05)...
others have failed to describe an association between high calcium intake and formation of kidney stones.1414 Curhan GC, Willett WC, Rimm EB, Stampfer MJ. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med 1993;328:833-8. PMID: 8441427 DOI: http://dx.doi.org/10.1056/NEJM199303253281203
http://dx.doi.org/10.1056/NEJM1993032532...
, 3434 Curhan GC, Willett WC, Knight EL, Stampfer MJ. Dietary factors and the risk of incident kidney stones in younger women: Nurses' Health Study II. Arch Intern Med 2004;164:885-91. PMID: 15111375 DOI: http://dx.doi.org/10.1001/archinte.164.8.885
http://dx.doi.org/10.1001/archinte.164.8...
Other authors have also reported decreased formation of kidney stones in subjects on high calcium diets.1717 Taylor EN, Stampfer MJ, Curhan GC. Dietary factors and the risk of incident kidney stones in men: new insights after 14 years of follow-up. J Am Soc Nephrol 2004;15:3225-32. DOI: http://dx.doi.org/10.1097/01.ASN.0000146012.44570.20
http://dx.doi.org/10.1097/01.ASN.0000146...
, 3434 Curhan GC, Willett WC, Knight EL, Stampfer MJ. Dietary factors and the risk of incident kidney stones in younger women: Nurses' Health Study II. Arch Intern Med 2004;164:885-91. PMID: 15111375 DOI: http://dx.doi.org/10.1001/archinte.164.8.885
http://dx.doi.org/10.1001/archinte.164.8...
According to Voss et al.,2929 Voss S, Hesse A, Zimmermann DJ, Sauerbruch T, von Unruh GE. Intestinal oxalate absorption is higher in idiopathic calcium oxalate stone formers than in healthy controls: measurements with the [(13)C2]oxalate absorption test. J Urol 2006;175:1711-5. DOI: http://dx.doi.org/10.1016/S0022-5347(05)01001-3
http://dx.doi.org/10.1016/S0022-5347(05)...
diets with adequate calcium levels (1000-1200 mg/day) play an important role for patients more prone to forming calcium oxalate stones. Taylor et al.1717 Taylor EN, Stampfer MJ, Curhan GC. Dietary factors and the risk of incident kidney stones in men: new insights after 14 years of follow-up. J Am Soc Nephrol 2004;15:3225-32. DOI: http://dx.doi.org/10.1097/01.ASN.0000146012.44570.20
http://dx.doi.org/10.1097/01.ASN.0000146...
evaluated a group of men and found that higher calcium intake was associated with reduced risk of renal lithiasis. However, this association was not observed in men aged 60 years or older. Another study found that adequate calcium, low protein, and low salt intake decrease urinary oxalate excretion and may explain the reduction in the risk of recurrent nephrolithiasis versus a diet low in calcium alone. The authors commented that this difference could be related to different levels of oxalate excretion pursuant to each diet.2828 Borghi L, Schianchi T, Meschi T, Guerra A, Allegri F, Maggiore U, et al. Comparison of two diets for the prevention of recurrent stones in idiopathic hypercalciuria. N Engl J Med 2002;346:77-84. PMID: 11784873 DOI: http://dx.doi.org/10.1056/NEJMoa010369
http://dx.doi.org/10.1056/NEJMoa010369...
Some studies have indicated that when calcium is administered in the form of a supplement there is a 20% increase in the relative risk of kidney stone formation.3636 Curhan GC, Willett WC, Rimm EB, Spiegelman D, Stampfer MJ. Prospective study of beverage use and the risk of kidney stones. Am J Epidemiol 1996;143:240-7. PMID: 8561157 DOI: http://dx.doi.org/10.1093/oxfordjournals.aje.a008734
http://dx.doi.org/10.1093/oxfordjournals...
, 3737 Curhan GC, Willett WC, Speizer FE, Spiegelman D, Stampfer MJ. Comparison of dietary calcium with supplemental calcium and other nutrients as factors affecting the risk for kidney stones in women. Ann Intern Med 1997;126:497-504. PMID: 9092314 DOI: http://dx.doi.org/10.7326/0003-4819-126-7-199704010-00001
http://dx.doi.org/10.7326/0003-4819-126-...
Therefore, a daily intake of 800-1200 mg of calcium from food sources is recommended.7Sociedade Brasileira de Nefrologia. Diretrizes de litíase urinária. J Bras Nefrol 2002;24:203-7.

Both groups had low levels of potassium intake. Reduced potassium intake increases calcium urinary excretion and the risk of kidney stone formation.1717 Taylor EN, Stampfer MJ, Curhan GC. Dietary factors and the risk of incident kidney stones in men: new insights after 14 years of follow-up. J Am Soc Nephrol 2004;15:3225-32. DOI: http://dx.doi.org/10.1097/01.ASN.0000146012.44570.20
http://dx.doi.org/10.1097/01.ASN.0000146...
Taylor & Curhan9Taylor EM, Curhan GC. Oxalate intake and the risk for nephrolithiasis. J Am Soc Nephrol 2007;18:2198-204. DOI: http://dx.doi.org/10.1681/ASN.2007020219
http://dx.doi.org/10.1681/ASN.2007020219...
reviewed the Health Professionals Follow-up Study (HPFS) and The Nurses' Health Studies I and II (NHS I and NHS II) and concluded that potassium intake was inversely associated with the risk of forming kidney stones; however, this effect was not seen in young women. Other studies have also found that potassium intake is inversely related to the formation of renal calculi1414 Curhan GC, Willett WC, Rimm EB, Stampfer MJ. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med 1993;328:833-8. PMID: 8441427 DOI: http://dx.doi.org/10.1056/NEJM199303253281203
http://dx.doi.org/10.1056/NEJM1993032532...
, 1717 Taylor EN, Stampfer MJ, Curhan GC. Dietary factors and the risk of incident kidney stones in men: new insights after 14 years of follow-up. J Am Soc Nephrol 2004;15:3225-32. DOI: http://dx.doi.org/10.1097/01.ASN.0000146012.44570.20
http://dx.doi.org/10.1097/01.ASN.0000146...
and may be an important factor in reducing the recurrence of kidney stones.1717 Taylor EN, Stampfer MJ, Curhan GC. Dietary factors and the risk of incident kidney stones in men: new insights after 14 years of follow-up. J Am Soc Nephrol 2004;15:3225-32. DOI: http://dx.doi.org/10.1097/01.ASN.0000146012.44570.20
http://dx.doi.org/10.1097/01.ASN.0000146...

No significant differences between groups were seen for vitamin C intake, although 83.9% of the individuals with nephrolithiasis had low levels of vitamin C intake. A study carried out with a group of male individuals with vitamin C intake levels adjusted for age found no association between the formation of kidney stones and vitamin C intake.1717 Taylor EN, Stampfer MJ, Curhan GC. Dietary factors and the risk of incident kidney stones in men: new insights after 14 years of follow-up. J Am Soc Nephrol 2004;15:3225-32. DOI: http://dx.doi.org/10.1097/01.ASN.0000146012.44570.20
http://dx.doi.org/10.1097/01.ASN.0000146...
Another study showed that high doses of vitamin C supplements increased the risk of calcium oxalate stones being formed.3535 Curhan GC, Willett WC, Speizer FE, Stampfer MJ. Twenty-four-hour urine chemistries and the risk of kidney stones among women and men. Kidney Int 2001;59:2290-8. PMID: 11380833 Traxer et al.3838 Traxer O, Huet B, Poindexter J, Pak CY, Pearle MS. Effect of ascorbic acid consumption on urinary stone risk factors. J Urol 2003;170:397-401. PMID: 12853784 DOI: http://dx.doi.org/10.1097/01.ju.0000076001.21606.53
http://dx.doi.org/10.1097/01.ju.00000760...
indicated that 1000 mg of vitamin C supplements ingested twice a day increased urinary oxalate excretion by 20% to 33%. However, Auer et al.3939 Auer BL, Auer D, Rodgers AL. The effect of ascorbic acid ingestion on the biochemical and physicochemical risk factors associated with calcium oxalate kidney stone formation. Clin Chem Lab Med 1998;36:143-7. PMID: 9589801 DOI: http://dx.doi.org/10.1515/CCLM.1998.027
http://dx.doi.org/10.1515/CCLM.1998.027...
reported that intakes of up to 4 g/day of vitamin C did not increase oxalate excretion. The benefit generated by the intake of lemon or orange juice was probably caused by the increase in water intake.

The mean intakes of vitamin C observed in our study were 48.96 mg/day for patients in the NL group and 37.26 mg/day for controls. The vitamin C intake levels seen in this study were lower than the values observed in the POF 2008-20093333 Brasil. Fundação IBGE. Pesquisa de orçamento familiar-2008/2009. Análise do consumo alimentar pessoal no Brasil. Rio de Janeiro; 2011. for the Brazilian population in general and the population living in the South of the country.

According to the POF 2008-2009,3333 Brasil. Fundação IBGE. Pesquisa de orçamento familiar-2008/2009. Análise do consumo alimentar pessoal no Brasil. Rio de Janeiro; 2011. the mean intake of vitamin C of individuals within the same age range as the subjects in our study ranged from 155.9 mg/day to 167.2 mg/day for males, and 142.7 mg/day to 167.9 mg/day for females. The population living in the South had mean vitamin C intakes ranging from 102 mg/day to 122.6 mg/ day for females, and 115.9 mg/day to 83.2 mg/ day for males. However, it is important to note that in the dietary assessment methodology used in the POF (2008-2009)3333 Brasil. Fundação IBGE. Pesquisa de orçamento familiar-2008/2009. Análise do consumo alimentar pessoal no Brasil. Rio de Janeiro; 2011. the food intakes on two non-consecutive days were recorded, while our study used 24-hour dietary recalls, which may underestimate food intake.

No significant difference between groups was seen in oxalate intake. Subjects in the NL group had a mean intake of 159 mg/day (± 119.27), and 100% of the enrolled individuals had inadequate levels of oxalate intake. In contrast, 90.5% of the individuals in the NL group had adequate levels of oxalate excretion, indicating a possible overestimation in the assessment of oxalate intake. This fact may be explained by the dietary survey used in the study, as the FFQ is a more subjective method, and by the methodological steps taken in an attempt to estimate daily oxalate intake. Holmes et al.1111 Holmes RP, Goodman HO, Assimos DG. Contribution of dietary oxalate to urinary oxalate excretion. Kidney Int 2001;59:270-6. PMID: 11135080 DOI: http://dx.doi.org/10.1046/j.1523-1755.2001.00488.x
http://dx.doi.org/10.1046/j.1523-1755.20...
showed that urinary oxalate excretion increases as oxalate intake is increased. Other authors consider the restriction of oxalaterich foods essential for patients with diet-related hyperoxaluria.8Gomes PN. Profilaxia da litíase renal. Acta Urol 2005;22;3:47-56. Patients with nephrolithiasis have been reported to have greater absorption of oxalate.1111 Holmes RP, Goodman HO, Assimos DG. Contribution of dietary oxalate to urinary oxalate excretion. Kidney Int 2001;59:270-6. PMID: 11135080 DOI: http://dx.doi.org/10.1046/j.1523-1755.2001.00488.x
http://dx.doi.org/10.1046/j.1523-1755.20...
, 2929 Voss S, Hesse A, Zimmermann DJ, Sauerbruch T, von Unruh GE. Intestinal oxalate absorption is higher in idiopathic calcium oxalate stone formers than in healthy controls: measurements with the [(13)C2]oxalate absorption test. J Urol 2006;175:1711-5. DOI: http://dx.doi.org/10.1016/S0022-5347(05)01001-3
http://dx.doi.org/10.1016/S0022-5347(05)...
Even low-oxalate diets offering as little as 10 mg/day of the substance may result in effective absorption and significant contribution to urinary oxalate excretion.1111 Holmes RP, Goodman HO, Assimos DG. Contribution of dietary oxalate to urinary oxalate excretion. Kidney Int 2001;59:270-6. PMID: 11135080 DOI: http://dx.doi.org/10.1046/j.1523-1755.2001.00488.x
http://dx.doi.org/10.1046/j.1523-1755.20...
However, Curhan et al.1414 Curhan GC, Willett WC, Rimm EB, Stampfer MJ. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med 1993;328:833-8. PMID: 8441427 DOI: http://dx.doi.org/10.1056/NEJM199303253281203
http://dx.doi.org/10.1056/NEJM1993032532...
did not find an association between the intake of oxalate-rich foods and risk of forming kidney stones. Voss et al.2929 Voss S, Hesse A, Zimmermann DJ, Sauerbruch T, von Unruh GE. Intestinal oxalate absorption is higher in idiopathic calcium oxalate stone formers than in healthy controls: measurements with the [(13)C2]oxalate absorption test. J Urol 2006;175:1711-5. DOI: http://dx.doi.org/10.1016/S0022-5347(05)01001-3
http://dx.doi.org/10.1016/S0022-5347(05)...
suggested that patients should be tested for oxalate absorption, so that individualized treatment was offered to subjects with higher absorption levels.

Protein intake did not yield statistically significant differences between groups. However, 54.2% of the individuals in the NL group had high protein intake levels. Some have argued that increased protein intake may increase the formation of renal calculi, given that animal protein intake increases the urinary excretion of calcium,7Sociedade Brasileira de Nefrologia. Diretrizes de litíase urinária. J Bras Nefrol 2002;24:203-7. , 1010 Sociedade Brasileira de Urologia. Litíase urinária: aspectos metabológicos em adultos e crianças; 2006. , 1717 Taylor EN, Stampfer MJ, Curhan GC. Dietary factors and the risk of incident kidney stones in men: new insights after 14 years of follow-up. J Am Soc Nephrol 2004;15:3225-32. DOI: http://dx.doi.org/10.1097/01.ASN.0000146012.44570.20
http://dx.doi.org/10.1097/01.ASN.0000146...
, 4040 Allen LH, Oddoye EA, Margen S. Protein-induced hypercalciuria: a longer term study. Am J Clin Nutr 1979;32:741-9. PMID: 433806 and oxalate,7Sociedade Brasileira de Nefrologia. Diretrizes de litíase urinária. J Bras Nefrol 2002;24:203-7. while it reduces citrate excretion7Sociedade Brasileira de Nefrologia. Diretrizes de litíase urinária. J Bras Nefrol 2002;24:203-7. , 8Gomes PN. Profilaxia da litíase renal. Acta Urol 2005;22;3:47-56. , 1010 Sociedade Brasileira de Urologia. Litíase urinária: aspectos metabológicos em adultos e crianças; 2006. , 1717 Taylor EN, Stampfer MJ, Curhan GC. Dietary factors and the risk of incident kidney stones in men: new insights after 14 years of follow-up. J Am Soc Nephrol 2004;15:3225-32. DOI: http://dx.doi.org/10.1097/01.ASN.0000146012.44570.20
http://dx.doi.org/10.1097/01.ASN.0000146...
and urine pH.1010 Sociedade Brasileira de Urologia. Litíase urinária: aspectos metabológicos em adultos e crianças; 2006. Curhan et al.1414 Curhan GC, Willett WC, Rimm EB, Stampfer MJ. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med 1993;328:833-8. PMID: 8441427 DOI: http://dx.doi.org/10.1056/NEJM199303253281203
http://dx.doi.org/10.1056/NEJM1993032532...
found that animal protein intake increases the excretion of uric acid and calcium, and decreases the excretion of citrate, predisposing individuals to the formation of kidney stones. Another study carried out with an exclusively male population found that the risk associated with animal protein intake varied according to the BMI. Animal protein intake has been associated with increased formation of renal calculi only in men with a BMI < 25 kg/m2.1717 Taylor EN, Stampfer MJ, Curhan GC. Dietary factors and the risk of incident kidney stones in men: new insights after 14 years of follow-up. J Am Soc Nephrol 2004;15:3225-32. DOI: http://dx.doi.org/10.1097/01.ASN.0000146012.44570.20
http://dx.doi.org/10.1097/01.ASN.0000146...
Reductions in protein intake have been thought to result in reduced endogenous synthesis of oxalate.4141 Conyers RA, Bais R, Rofe AM. The relation of clinical catastrophes, endogenous oxalate production, and urolithiasis. Clin Chem 1990;36:1717-30. However, controversy still looms over this topic, as some studies point to increases in the rate of recurrent nephrolithiasis in individuals on dietary animal protein restriction,4242 Hiatt RA, Ettinger B, Caan B, Quesenberry CP Jr, Duncan D, Citron JT. Randomized controlled trial of a low animal protein, high fiber diet in the prevention of recurrent calcium oxalate kidney stones. Am J Epidemiol 1996;144:25-33. PMID: 8659482 DOI: http://dx.doi.org/10.1093/oxfordjournals.aje.a008851
http://dx.doi.org/10.1093/oxfordjournals...
while others fail to report associations between protein intake and increased risk of kidney stones.3232 Powell CR, Stoller ML, Schwartz BF, Kane C, Gentle DL, Bruce JE, et al. Impact of body weight on urinary electrolytes in urinary stone formers. Urology 2000;55:825-30. PMID: 10840085 DOI: http://dx.doi.org/10.1016/S0090-4295(99)00617-2
http://dx.doi.org/10.1016/S0090-4295(99)...

No statistical difference between groups was seen in water intake. However, it is recommended that patients with kidney stones drink at least 2.5 liters/day of water.3636 Curhan GC, Willett WC, Rimm EB, Spiegelman D, Stampfer MJ. Prospective study of beverage use and the risk of kidney stones. Am J Epidemiol 1996;143:240-7. PMID: 8561157 DOI: http://dx.doi.org/10.1093/oxfordjournals.aje.a008734
http://dx.doi.org/10.1093/oxfordjournals...
Interestingly, 67.7% of the patients in the NL group had inadequate intake levels, as they had no more than two liters of water per day. Adequate fluid intake is considered essential for patients with kidney stones, as it decreases urinary saturation and prevents the occurrence of various stages of stone formation.8Gomes PN. Profilaxia da litíase renal. Acta Urol 2005;22;3:47-56. Other studies have also indicated that water intake is inversely related to the risk of forming kidney stones.8Gomes PN. Profilaxia da litíase renal. Acta Urol 2005;22;3:47-56. , 1414 Curhan GC, Willett WC, Rimm EB, Stampfer MJ. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med 1993;328:833-8. PMID: 8441427 DOI: http://dx.doi.org/10.1056/NEJM199303253281203
http://dx.doi.org/10.1056/NEJM1993032532...
, 1717 Taylor EN, Stampfer MJ, Curhan GC. Dietary factors and the risk of incident kidney stones in men: new insights after 14 years of follow-up. J Am Soc Nephrol 2004;15:3225-32. DOI: http://dx.doi.org/10.1097/01.ASN.0000146012.44570.20
http://dx.doi.org/10.1097/01.ASN.0000146...

Borghi et al.4343 Borghi L, Meschi T, Amato F, Briganti A, Novarini A, Giannini A. Urinary volume, water and recurrences in idiopathic calcium nephrolithiasis: a 5-year randomized prospective study. J Urol 1996;155:839-43. PMID: 8583588 DOI: http://dx.doi.org/10.1016/S0022-5347(01)66321-3
http://dx.doi.org/10.1016/S0022-5347(01)...
studied patients with idiopathic calcium nephrolithiasis and noted that adequate water intake, even when not accompanied by dietary changes, may have a positive effect against recurrence in many patients. A significant increase in urine volume was observed in the individuals enrolled in a study that followed patients advised to increase water intake levels among other things.1212 Carvalho M, Ferrari ACH, Renner LO, Vieira MA, Riella MC. Quantificação do Stone Clinic Effect em pacientes com nefrolitíase. Rev Assoc Med Bras 2004;50:79-82. DOI: http://dx.doi.org/10.1590/S0104-42302004000100040
http://dx.doi.org/10.1590/S0104-42302004...
Carvalho et al.1212 Carvalho M, Ferrari ACH, Renner LO, Vieira MA, Riella MC. Quantificação do Stone Clinic Effect em pacientes com nefrolitíase. Rev Assoc Med Bras 2004;50:79-82. DOI: http://dx.doi.org/10.1590/S0104-42302004000100040
http://dx.doi.org/10.1590/S0104-42302004...
advised a group of individuals to increase water intake, decrease salt and protein (approximately 1 g/kg/day) intake, and have 800 mg/day of calcium; significant increases in urinary citrate (368 ± 238 mg/day vs. 502 ± 221 mg/ day) were observed subsequently. A normal-calcium, low-salt, low-protein diet decreases urinary excretion of oxalate and calcium. When combined with increased water intake, this diet results in decreased urinary saturation and reduced recurrence of kidney stones.2828 Borghi L, Schianchi T, Meschi T, Guerra A, Allegri F, Maggiore U, et al. Comparison of two diets for the prevention of recurrent stones in idiopathic hypercalciuria. N Engl J Med 2002;346:77-84. PMID: 11784873 DOI: http://dx.doi.org/10.1056/NEJMoa010369
http://dx.doi.org/10.1056/NEJMoa010369...

The patients in the NL group had more adequate citrate excretion levels than the subjects in the control group. Contrary to what has been published by other authors, in the NL group 90.5% of the individuals had adequate citrate excretion levels, versus 55.6% of the subjects in the control group. Peres et al.2Peres LAB, Almeida LP, Bolson LB, Brites MF, David JM, Tazima L. Investigação de nefrolitíase no Oeste do Paraná. J Bras Nefrol 2011;33:160-5. DOI: http://dx.doi.org/10.1590/S0101-28002011000200007
http://dx.doi.org/10.1590/S0101-28002011...
described hypocitraturia in 23.5% of the patients with nephrolithiasis. Ferraz et al.3Ferraz FHRP, Carvalho PRA, Souza RR. Perfil dos pacientes portadores de nefrolitíase em tratamento ambulatorial em um hospital público do Distrito Federal. Brasília Med 2011;48:252-7. studied 150 patients with nephrolithiasis and found that 29.5% of them had hypocitraturia. Carvalho et al.1212 Carvalho M, Ferrari ACH, Renner LO, Vieira MA, Riella MC. Quantificação do Stone Clinic Effect em pacientes com nefrolitíase. Rev Assoc Med Bras 2004;50:79-82. DOI: http://dx.doi.org/10.1590/S0104-42302004000100040
http://dx.doi.org/10.1590/S0104-42302004...
reported that 44% of the patients with nephrolithiasis had a mean citrate excretion of 178 ± 93.3 mg/ day and were considered to have hypocitraturia by the author. Thus, hypocitraturia has been considered as a risk factor for the development of kidney stones.8Gomes PN. Profilaxia da litíase renal. Acta Urol 2005;22;3:47-56. , 1414 Curhan GC, Willett WC, Rimm EB, Stampfer MJ. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med 1993;328:833-8. PMID: 8441427 DOI: http://dx.doi.org/10.1056/NEJM199303253281203
http://dx.doi.org/10.1056/NEJM1993032532...
, 1717 Taylor EN, Stampfer MJ, Curhan GC. Dietary factors and the risk of incident kidney stones in men: new insights after 14 years of follow-up. J Am Soc Nephrol 2004;15:3225-32. DOI: http://dx.doi.org/10.1097/01.ASN.0000146012.44570.20
http://dx.doi.org/10.1097/01.ASN.0000146...
The results seen in our study may be explained by the directions possibly given to the patients by their physicians when they were diagnosed with nephrolithiasis.

No statistically significant differences were observed between groups in relation to urinary oxalate excretion. However, 9.5% of the individuals in the NL group had inadequate oxalate excretion levels. Urinary oxalate is a major factor in the formation of calcium oxalate kidney stones,2929 Voss S, Hesse A, Zimmermann DJ, Sauerbruch T, von Unruh GE. Intestinal oxalate absorption is higher in idiopathic calcium oxalate stone formers than in healthy controls: measurements with the [(13)C2]oxalate absorption test. J Urol 2006;175:1711-5. DOI: http://dx.doi.org/10.1016/S0022-5347(05)01001-3
http://dx.doi.org/10.1016/S0022-5347(05)...
, 4444 Troxel SA, Sidhu H, Kaul P, Low RK. Intestinal Oxalobacter formigenes colonization in calcium oxalate stone formers and its relation to urinary oxalate. J Endourol 2003;17:173-6. DOI: http://dx.doi.org/10.1089/089277903321618743
http://dx.doi.org/10.1089/08927790332161...
and even small increases in urinary oxalate excretion may increase the risk of patients forming calcium oxalate stones.9Taylor EM, Curhan GC. Oxalate intake and the risk for nephrolithiasis. J Am Soc Nephrol 2007;18:2198-204. DOI: http://dx.doi.org/10.1681/ASN.2007020219
http://dx.doi.org/10.1681/ASN.2007020219...
, 1414 Curhan GC, Willett WC, Rimm EB, Stampfer MJ. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med 1993;328:833-8. PMID: 8441427 DOI: http://dx.doi.org/10.1056/NEJM199303253281203
http://dx.doi.org/10.1056/NEJM1993032532...
, 1717 Taylor EN, Stampfer MJ, Curhan GC. Dietary factors and the risk of incident kidney stones in men: new insights after 14 years of follow-up. J Am Soc Nephrol 2004;15:3225-32. DOI: http://dx.doi.org/10.1097/01.ASN.0000146012.44570.20
http://dx.doi.org/10.1097/01.ASN.0000146...
Peres et al.2Peres LAB, Almeida LP, Bolson LB, Brites MF, David JM, Tazima L. Investigação de nefrolitíase no Oeste do Paraná. J Bras Nefrol 2011;33:160-5. DOI: http://dx.doi.org/10.1590/S0101-28002011000200007
http://dx.doi.org/10.1590/S0101-28002011...
described hyperoxaluria in 8.0% of the patients with nephrolithiasis, similarly to what was found in our study.

A limitation of our study was the small number of patients enrolled - a fact that stresses the need for studies with a greater number of individuals.

Additionally, the 24-hour dietary recall was used to quantify the previous day's food intake - a method that should be preferably applied for more than one non-consecutive day, allowing thereby a closer estimation of the actual food intake of each patient.4545 Buzzard M. 24-Hour Dietary recall and food record methods. In: Willet W. Nutritional epidemiology. 2nd ed. New York: Oxford University Press; 1998. p.51-67. This assessment instrument has been put to good use in epidemiological studies, as there is no variation on the mean food intake of the population from one day to the next.4646 Cintra IP, Von der Heyde MED, Schmitz BAS, Franceschini SCC, Taddei JAAC, Sigulem DM. Métodos de inquéritos dietéticos. Sociedade Brasileira de Alimentação e Nutrição. Cad Nutr 1997;13:11-23. Another fact to consider is the method's simplicity of use and quick application, which have made it widely adopted in the world. Although this method does not interfere with the feeding behavior of the individuals and relies on the subject's memories of a recent past, the 24-hour dietary recall seems to underestimate the intake of certain nutrients, especially when applied for one day only.4747 Gibson RS. Principles of Nutritional Assessment. New York: Oxford University Press; 1990. p.161. , 4848 Freudenheim JL. A review of study designs and methods of dietary assessment in nutritional epidemiology of chronic disease. J Nutr 1993;123:401-5. This method also relies considerably on the subject's perception over the size of the food servings.4949 Slater B, Philippi ST, Marchioni DML, Fisberg RM. Validação de Questionários de Frequência Alimentar - QFA: considerações metodológicas. Rev Bras Epidemiol 2003;6:200-8. DOI: http://dx.doi.org/10.1590/S1415-790X2003000300003
http://dx.doi.org/10.1590/S1415-790X2003...

Conclusions

This study served as a basis to improve the understanding of the metabolic profile and food intake pattern of patients with kidney stones treated at the Hospital de Clinicas of the Federal University of Paraná. Both groups were found to have a high prevalence of overweight individuals, high levels of oxalate and calcium intake, and inadequate levels of calcium, potassium and vitamin C intake. The subjects in the NL group had high levels of protein intake and citrate excretion. Knowledge of the factors associated with the formation of kidney stones may optimize the nutritional care offered to patients with nephrolithiasis.

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  • Erratum

    The paper: "Evaluation of food intake and excretion of metabolites in nephrolithiasis", published in the October 2014 issue of the Brazilian Journal of Nephrology [J Bras Nefrol. 2014; 36: 437-445] there has been a change made to the Table 1 of this paper, and we added another author: Maurício Carvalho.

Publication Dates

  • Publication in this collection
    Oct-Dec 2014

History

  • Received
    09 Jan 2014
  • Accepted
    17 May 2014
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