Main Nutritional Lithogenic Factors in Diets of Polish Patients with Kidney Stones

Background. Nutrition is one of the most important determinants of kidney stone formation. This study was designed to evaluate lithogenic factors in diet of patients with renal calculi. Materials and methods. 40 stone-formers without metabolic disorders stimulating stone formation (e.g. hyperparatyroidism, primary hyperoxaluria) were invited to the study. Antropometric measurements of nutritional status (BMI, WHR), analysis of body composition (BIA), quality and quantitative analysis of patients’ eating habits (3-day food records) were conducted. Results. Half of patients were overweight or obese. Their diets contained high amounts of protein, fat, phosphorus, vitamin C and low amounts of fluid, calcium, magnesium, potassium, vitamin B6. Protein consumption was positively correlated with uric acid intake in diets (r = 0.78), and body weight with dietary fat intake (r = 0.58) and uric acid intake (r = 0.55). Conclusions. Complete treatment of nephrolithiasis should include nutritional therapy. No change in customary diets of patients with renal calculi can stimulate lithogenesis process.


Introduction
Kidney stone (renal calculus, lat.nephrolithasis, urolithasis) is the third most frequent urinary disease.It occurs on the entire world and affects up to 5 % of the population between 30 and 50 years old which indicates that the disease is a serious social issue in industrialized countries prevalence of nephrolithiasis ranges from 1 to 10 %.Most kidney stones are composed of calcium salts (oxalate, phosphate) [1,2].The main causes of stone formation are genetic and environmental factors.Family history of kidney calculi enhances its incidence [3].Some scientists called nephrolithiasis a "nutritional disease".A significant role in ethiology of the disease is a diet.Diets rich in fat (indirectly) and animal protein (directly) stimulate lithogenesis [4].In our study we tried to find basic nutritional factors among patients with kidney stones, which may be lithogenic factors.

Materials and methods
We invited patients with kidney stones from Kolejowy Central Hospital, Baby Jesus Hospital Nephrological-Transplant Clinic and Individual Specialistic Medical Practice in Urology Clinic in Gdansk treating patients with urinary tract diseases, including kidney stone, to take part in the study.
The exclusion criteria were hyperparatyroidism, primary hyperoxaluria or other metabolic disorders stimulating stone formation.42 patients gave their assent to participate in the study.None of them received any specific dietary consultation before the study.Glomural filtration rate was estimated on the basis of Levey et al. formula [5].Body Mass Index (BMI) and Waist-Hips Ratio (WHR) were calculated as weight (kg) divided by height squared (m 2 ) and waistline (cm) divided by hips line (m), adequately.Bioimpedance was done according to standardised procedures [6].In this analysis we used 3-day food records and also on their basis we specified energy and other nutrients intake by means of a computer software Dietetyk, based on Polish Food Nutrition Tables [7].The results are presented as mean ± SD.BMI, energy, n3, n3/n6 and fibre intakes, because the lack of normal distribution is presented as the median.Since the study was conducted before 2008 the results referred to dietary guidelines for Poland of that time [8].To describe differences between men and women we used Student's test and nonparametric Mann-Whitney

Results
The characteristics of 42 stone formers are presented in Table 1.There was not any difference in the age of patients, but men had higher BMI and WHR.Among 28 participants with long history of nephrolithiasis (more than 3 years) occurred episodes of recurrence of kidney stones.The most common components of calculi were oxalate salts.A family history of kidney stones occurred with 24 patients.The efficiency of kidney measured by glomular filtration rate indicated mainly not significant kidney's impairment.Only in two women kidney stones essentially damaged renal function (Table 2).Men had higher and statistically significant BMI and WHR parameters (Table 1), compared with women.The waistlines of 50 % men were more than 102 cm.Bioelectrical Impedance Analysis test was performed on 42 patients with kidney stones.Only 7 participants had normal percentage of body fat but the total body water, as an estimate of hydration level, was insufficient in 35 persons.Results of quantitative analysis menu patients with nephrolithiasis are summarized in Table 3. Dietary energy intake in group of men was significantly higher than in the group of women which resulted from high intake of protein and fat in men's diets.Men also drank more fluids on a daily basis, compared with women, but in both groups this value was lower than recommended (more than 2.5 L per day) [9].We did not find any correlation between total fluid intake and total body water intake.Meat products eaten every day were the main source of protein in diets.We observed positive correlation between dietary total protein intake and uric acid intake as well (Fig. 1) although body weight of patients was correlated with dietary fat intake (Fig. 2) and uric acid intake (Fig. 3).Furthermore, inconsiderable correlation was found between dietary fat intake and body fat mass (p = 0.0506, r = 0.51).

Discussion
The first episode of nephrolithiasis may appear even in childhood triggered by primary hiperoxaluria [10,11] and in our study age range of patients with kidney stones was wide (23-76 years).Recurrent renal stone disease is very frequent and occurs in about 50 % stone formers [13].In most participants of the study stones recurred too and the most common type was oxalate salts just like in other studies [10,14].A family history of kidney stones enhanced the risk of development of the disease in individuals.Curhan et al. [13] in a cohort the Health Professionals Follow-up Study of 37 999 men showed that in male stone formers a family history of nephrolithiasis was more common than in those without kidney stones.Our study indicated the same relation.Long-term stone formation with recurrences may increase the risk of chronic kidney failure leading to glomerulosclerosis and decreased glomular filtration rate by obstruct calyces and renal pelvis [15].Two women in this study had very low GFR, which indicated almost end-stage renal di sease.Overweight and obesity may stimulate renal stones formation.Positive correlations between body weight, BMI and nephrolithiasis can be found in many studies [16,17].Maalouf et al. [18] and Abate et al. [19] revealed that excess percentage body fat and insulin resistance lower pH in urine enhance the risk of uric acid kidney stones.In our study most patients had quite high value of BMI, WHR (particularly men) and body fat (particularly women).Diets of patients with kidney stones supplied low intakes of fluids, fibre and high intakes of protein, fat, especially in a group of men.Diets with insufficient participation of fluid stimulate salts crystallisation in urine and stone formation [20].In this group additional lithegenic factor was type of beverages (first of all black tea and coffee), as we mentined in Roczn PZH [21].Excess animal protein in our studyand positive correlation with dietary uric acid intake may acidify urine and cause hypercalciuria [19][20][21][22].Giannini et al. [23] showed that 0.8 g protein/ kg/day significantly reduced serum and urinary urea values, similarly like urinary calcium and oxalate.Vegetarian diets, compared to the westerntype diets, decrease the risk of uric acid crystallisation by 93 % [24].But Massey and Kynast-Gales [25] revealed a more important relationship between protein intake than the type of protein.
Positive correlation between body weight of patients with kidney stones and fat intake implies that it could be the main cause of overweight and obesity and high percentage body fat among the participants.Additionally, higher uric acid consumption among patients with higher body weight can undoubtedly stimulate stone formation.On the other hand, fibre may protect from nephrolithiasis.Hess et al. [26] proved that fibre enhances urinary citrate Оригінальні статті / Original Articles excretion which dissolves calcium oxalate salts.However, in diets of our patients this nutrient was in insufficient intake as well, which indicates low consumption of fruit and vegetables.Low potassium and magnesium intake may stimulate stone formation by reduced reabsorption of calcium in tubule and decreased concentration of natural inhibitor of crystallisation of calcium oxalate, which is magnesium.Furthermore, among other nutritional litho-genic factors, which have been described by us in Roczn PZH [21], we can rate low diet intake of calcium, vitamin B 6 and high intake of oxalic acid, vitamin C.

Conclusions
Nutrition can stimulate lithogenesis.Patients with kidney stones should have an opportunity to talk to dietitians about their nutritional habits and receive accurate dietetic recommendations.

Figure 3 .
Figure 3. Correlation between body weight of patients with kidney stones and dietary fat intake (* -simple linear regression analysis)

Abstract. Background. Nutrition
is one of the most important determinants of kidney stone formation.This study was designed to evaluate lithogenic factors in diet of patients with renal calculi.

Materials and me- thods. 40
Complete treatment of nephrolithiasis should include nutritional therapy.No change in customary diets of patients with renal calculi can stimulate lithogenesis process.Том 6, № 4, 2017 Оригінальні статті / Original Articles test (STATGRAPHICS Plus 4.0).To evaluate correlation simple linear regression analysis was applied.