Effect of potential renal acid load of foods on urinary citrate excretion in calcium renal stone formers

Effects of higher dietary acid load: a narrative review with special emphasis in children

Metabolic effects of high diet acid load (DAL) have been studied for years in adults, although only recently in children. Contemporary diets, especially those of Western societies, owe their acidogenic effect to high animal-origin protein content and low contribution of base-forming elements, such as fruits and vegetables. This imbalance, where dietary acid precursors exceed the body's buffering capacity, results in an acid-retaining state known by terms such as "eubicarbonatemic metabolic acidosis," "low-grade metabolic acidosis," "subclinical acidosis," or "acid stress". Its consequences have been linked to chronic systemic inflammation, contributing to various noncommunicable diseases traditionally considered more common in adulthood, but now have been recognized to originate at much earlier ages. In children, effects of high DAL are not limited to growth impairment caused by alterations of bone and muscle metabolism, but also represent a risk factor for conditions such as obesity, insulin resistance, diabetes, hypertension, urolithiasis, and chronic kidney disease (CKD). The possibility that high DAL may be a cause of chronic acid-retaining states in children with growth impairment should alert pediatricians and pediatric nephrologists, since its causes have been attributed traditionally to inborn errors of metabolism and renal pathologies such as CKD and renal tubular acidosis. The interplay between DAL, overall diet quality, and its cascading effects on children's health necessitates comprehensive nutritional assessments and interventions. This narrative review explores the clinical relevance of diet-induced acid retention in children and highlights the potential for prevention through dietary modifications, particularly by increasing fruit and vegetable intake alongside appropriate protein consumption.

Dietary acid load in health and disease

Maintaining an appropriate acid-base equilibrium is crucial for human health. A primary influencer of this equilibrium is diet, as foods are metabolized into non-volatile acids or bases. Dietary acid load (DAL) is a measure of the acid load derived from diet, taking into account both the potential renal acid load (PRAL) from food components like protein, potassium, phosphorus, calcium, and magnesium, and the organic acids from foods, which are metabolized to bicarbonate and thus have an alkalinizing effect. Current Western diets are characterized by a high DAL, due to large amounts of animal protein and processed foods. A chronic low-grade metabolic acidosis can occur following a Western diet and is associated with increased morbidity and mortality. Nutritional advice focusing on DAL, rather than macronutrients, is gaining rapid attention as it provides a more holistic approach to managing health. However, current evidence for the role of DAL is mainly associative, and underlying mechanisms are poorly understood. This review focusses on the role of DAL in multiple conditions such as obesity, cardiovascular health, impaired kidney function, and cancer.

Potential Renal Acid Load, Salivary Buffer Capacity and Healthy Eating Index as Predictors of Children's Dental Caries: A Cross-Sectional Study

INTRODUCTION

Dental caries is one of the most common childhood diseases. This study purposed to investigate the prediction capability of potential renal acid load (PRAL), salivary buffer capacity (SBC), and Healthy Eating Index (HEI) on children's dental caries.

METHODS

The decay, missing, filing, and teeth for primary teeth (dmft)/Decay, Missing, Filling, and Teeth for permanent teeth (DMFT) indexes of the children aged 7-12 years who applied to our faculty were recorded. Approximately 1 mL of unstimulated saliva samples were collected, and SBC was evaluated. PRAL and HEI scores were calculated by entering the data in the form of a daily nutrition record of the children into the BeBiS software (Ebispro for Windows, Stuttgart, Germany). The association of dental caries indices with PRAL, SBC, and HEI was analyzed using an independent sample t-test. A binomial logistic regression analysis was performed to predict the dental caries burden. The statistical significance level was adjusted to a=0.05.

RESULTS

A total of 150 children, 88 (58.6%) females and 62 (41.4%) males, were included in the study. Significant differences were found between the low and high dental caries groups for dmft regarding PRAL and SBC (p<0.001). A significant difference was found between the low and high dental caries groups for DMFT in terms of SBC (p<0.05).

CONCLUSION

In our study, established regression models significantly predicted dental caries in primary teeth. SBC was the most influential factor in predicting dental caries compared to PRAL and HEI. There was a significant relationship between SBC, PRAL, and caries in primary teeth. In the model we created, the strongest predictor was SBC.

Chronic Sub-Clinical Systemic Metabolic Acidosis - A Review with Implications for Clinical Practice

When arterial serum pH remains near the lower pH limit of 7.35 for protracted periods of time, a low-grade, sub-clinical form of acidosis results, referred to in this review as chronic, sub-clinical, systemic metabolic acidosis (CSSMA). This narrative review explores the scientific basis for CSSMA, its consequences for health, and potential therapeutic interventions. The major etiology of CSSMA is the shift away from the ancestral, alkaline diet which was rich in fruit and vegetables, toward the contemporary, acidogenic 'Westernized' diet characterized by higher animal protein consumption and lack of base forming minerals. Urine pH is reduced with high dietary acid load and may be a convenient marker of CSSMA. Evidence suggests further that CSSMA negatively influences cortisol levels potentially contributing significantly to the pathophysiology thereof. Both CSSMA and high dietary acid load are associated with the risk and prognosis of various chronic diseases. Clinical trials show that CSSMA can be addressed successfully through alkalizing the diet by increasing fruit and vegetable intake and/or supplementing with alkaline minerals. This review confirms the existence of a significant body of evidence regarding this low-grade form of acidosis as well as evidence to support its diverse negative implications for health, and concludes that CSSMA is a condition warranting further research.

Observation and identification of autofluorescent urine crystals may be linked to a sign of urolithiasis

Urolithiasis is a common disease of the urinary system. Its recurrence rate is high and may increase medical expenses. Urine stones are composed of urine crystals and other impurities. We discovered the existence of autofluorescence in some of the urine crystals, especially in urolithiasis patients. The fluorescent molecule existed in urine crystals was verified and identified. We have applied micro-Raman and fluorescence microscopy to classify the urine crystals, used confocal laser scanning microscopy (CLSM) to examine the 3D images and spectra of autofluorescence in crystals, used Fourier-transform infrared spectroscopy (FTIR) and mass spectrometry (MS) to identify the type of fluorophore in the autofluorescent urine crystals in urine. Riboflavin was identified as one of the major fluorophores in these autofluorescent urine crystals. The prevalence rates of the autofluorescent crystals in urolithiasis patients and subjects without the history of urolithiasis were to gather statistics. We observed that 80% of urolithiasis patients had autofluorescent crystals. Contrastingly, such crystals existed in only 7% of subjects without the history of urolithiasis. The presence of autofluorescent urine crystals may be linked to a sign of urolithiasis.

Associations of Total Protein or Animal Protein Intake and Animal Protein Sources with Risk of Kidney Stones: A Systematic Review and Dose-Response Meta-Analysis

We conducted the present systematic review and meta-analysis to evaluate the association of total protein, animal protein, and animal protein sources with risk of kidney stones in the general population. A literature search was performed in PubMed/Medline, Scopus, and EMBASE up to July 2021. We assessed the credibility of evidence based on NutriGrade scoring system. A total of 14 prospective cohort studies were included. A positive association was observed between higher intake of nondairy animal protein (RR: 1.11; 95% CI: 1.03, 1.20; I2 = 0%, n = 4), total meat and meat products (RR: 1.22; 95% CI: 1.09, 1.38; I2 = 13%, n = 3), and processed meat (RR: 1.29; 95% CI: 1.10, 1.51; I2 = 0%, n = 2) with risk of kidney stones. There was an inverse association between higher intake of dairy protein and risk of kidney stones (RR: 0.91; 95% CI: 0.84, 0.99; I2 = 0%, n = 4). Moreover, each 100-gincrement of red meat intake was significantly associated with increased risk of kidney stones (RR: 1.39; 95% CI: 1.13, 1.71). According to the NutriGrade scoring system, the credibility of evidence for most of the exposures was rated as low. We found some kind of publication bias in the association of animal protein intake and risk of kidney stones, according to Egger's and Begg's tests. In the sensitivity analysis of processed meat as well as dairy consumption with risk of kidney stones we observed in each individual analysis, 1 study changed the overall estimate. Further observational studies are needed to confirm the present results. The protocol of the present study was registered in the International Prospective Register of Systematic Reviews (PROSPERO) database (CRD42021230125: https://www.crd.york.ac.uk/PROSPERO).

Higher Dietary Acid Load Is Associated With an Increased Risk of Calcium Oxalate Kidney Stones

OBJECTIVES

Diet-dependent net acid load may influence the risk of kidney stone formation by affecting calcium and citrate excretion. However, to date, little research has investigated the relationship between dietary acid load and kidney stones. Therefore, this study sought to assess whether a diet high in potential acid load was related to the risk of calcium oxalate stone formation.

METHODS

This case-control study was conducted on 430 participants (including 215 newly diagnosed patients with calcium oxalate stones and 215 controls matched for sex and age). Dietary intake was assessed using a validated food frequency questionnaire over the preceding year. Dietary acid load was estimated based on the potential renal acid load (PRAL) and net endogenous acid production (NEAP). The association between dietary acid load indices and kidney stone was examined using multivariable logistic regression.

RESULTS

Mean PRAL (standard error) was significantly lower in cases versus controls (-5.3 ± 1.3 vs. -1.7 ± 1.3, P = .048). Corresponding values for NEAP were 39.4 ± 0.8 and 41.8 ± 0.8, respectively (P = .032). After adjustment for potential confounders, the odds ratios (95% confidence intervals) of calcium oxalate stones in the top tertile of PRAL and NEAP were 1.45 (0.89-2.38, P = .136) and 1.88 (1.14-3.09, P = .013), respectively. Adjustment for potassium and protein in 2 separate models did not substantially change the results.

CONCLUSIONS

A diet high in potential acid load, measured by NEAP, was associated with higher risk of calcium oxalate stone formation, independent of potassium and protein intake. Prospective longitudinal studies are warranted to confirm the veracity of our results.

Risk of Kidney Stones: Influence of Dietary Factors, Dietary Patterns, and Vegetarian-Vegan Diets

Nephrolithiasis is a common medical condition influenced by multiple environmental factors, including diet. Since nutritional habits play a relevant role in the genesis and recurrence of kidney stones disease, dietary manipulation has become a fundamental tool for the medical management of nephrolithiasis. Dietary advice aims to reduce the majority of lithogenic risk factors, reducing the supersaturation of urine, mainly for calcium oxalate, calcium phosphate, and uric acid. For this purpose, current guidelines recommend increasing fluid intake, maintaining a balanced calcium intake, reducing dietary intake of sodium and animal proteins, and increasing intake of fruits and fibers. In this review, we analyzed the effects of each dietary factor on nephrolithiasis incidence and recurrence rate. Available scientific evidence agrees on the harmful effects of high meat/animal protein intake and low calcium diets, whereas high content of fruits and vegetables associated with a balanced intake of low-fat dairy products carries the lowest risk for incident kidney stones. Furthermore, a balanced vegetarian diet with dairy products seems to be the most protective diet for kidney stone patients. Since no study prospectively examined the effects of vegan diets on nephrolithiasis risk factors, more scientific work should be made to define the best diet for different kidney stone phenotypes.

Impact of food quantity and quality on the biochemical risk of renal stone formation

OBJECTIVE

This study evaluated the role of body mass index (BMI) and dietary potential renal acid load (PRAL) with urinary saturation for calcium oxalate (US-CaOx), calcium phosphate (US-CaP) and uric acid (US-UA) in renal stone formers.

MATERIALS AND METHODS

A retrospective analysis was conducted of laboratory data collected on 442 renal stone-forming patients. Demographic information, BMI and 24 h urinary samples were collected from patients on their regular diets. PRAL was calculated as the Load of Acid to Kidney Evaluation (LAKE) score through a short questionnaire.

RESULTS

Urinary risk factors, but also inhibitors of calcium stone formation such as magnesium, tended to increase in relation to BMI (p = .000). Urinary pH (p = .002) and ammonium/sulfate ratio (p = .000) were negatively related to BMI. This resulted in a positive correlation between BMI and US-UA (p = .000), whereas US-CaOx and US-CaP were not influenced by BMI. LAKE score was positively correlated with US-CaOx (p = .022) and US-CaP (p = .000) as a consequence of the inverse relationship between LAKE score and citrate (p = .000). Multiple linear regression analysis identified BMI (p = .009) and male gender (p = .002) as independent predictors of US-UA, and LAKE score (p = .004) and age (p = .001) as independent predictors of US-CaP.

CONCLUSIONS

BMI, which depends on excessive intake of energy from food, is not related to an increased biochemical risk of calcium stone formation, which is more dependent on the renal acid load of the diet. In contrast, obesity is associated with an increased risk of uric acid stone formation due to insulin resistance, impaired ammoniagenesis and low urinary pH.

Urinary Stone Disease: Diagnosis, Medical Therapy, and Surgical Management

Clinical suspicion of urolithiasis should be evaluated with low-dose computed tomography as the first-line imaging modality for nonpregnant, adult patients. A period of observation may be appropriate for ureteral stones less than 10 mm, and medical expulsive therapy may be beneficial for facilitating passage of distal ureteral stones. Regardless of stone type, patients should adhere to a low-sodium diet and attempt to achieve a urine volume of more than 2.5 L daily. Individuals with calcium stones should maintain a normal calcium diet, and if stones persist, citrate therapy or thiazide diuretics in the setting of hypercalciuria may be indicated.

Diet-Induced Low-Grade Metabolic Acidosis and Clinical Outcomes: A Review

Low-grade metabolic acidosis is a condition characterized by a slight decrease in blood pH, within the range considered normal, and feeding is one of the main factors that may influence the occurrence of such a condition. The excessive consumption of acid precursor foods (sources of phosphorus and proteins), to the detriment of those precursors of bases (sources of potassium, calcium, and magnesium), leads to acid-base balance volubility. If this condition occurs in a prolonged, chronic way, low-grade metabolic acidosis can become significant and predispose to metabolic imbalances such as kidney stone formation, increased bone resorption, reduced bone mineral density, and the loss of muscle mass, as well as the increased risk of chronic diseases such as type 2 diabetes mellitus, hypertension, and non-alcoholic hepatic steatosis. Considering the increase in the number of studies investigating the influence of diet-induced metabolic acidosis on clinical outcomes, this review gathers the available evidence evaluating the association of this disturbance and metabolic imbalances, as well as related mechanisms. It is necessary to look at the western dietary pattern of most countries and the increasing incidence of non-comunicable diseases for the balance between fruit and vegetable intake and the appropriate supply of protein, mainly from animal sources, so that it does not exceed the daily recommendations.

Metabolic diagnosis and medical prevention of calcium nephrolithiasis and its systemic manifestations: a consensus statement

BACKGROUND

Recently published guidelines on the medical management of renal stone disease did not address relevant topics in the field of idiopathic calcium nephrolithiasis, which are important also for clinical research.

DESIGN

A steering committee identified 27 questions, which were proposed to a faculty of 44 experts in nephrolithiasis and allied fields. A systematic review of the literature was conducted and 5216 potentially relevant articles were selected; from these, 407 articles were deemed to provide useful scientific information. The Faculty, divided into working groups, analysed the relevant literature. Preliminary statements developed by each group were exhaustively discussed in plenary sessions and approved.

RESULTS

Statements were developed to inform clinicians on the identification of secondary forms of calcium nephrolithiasis and systemic complications; on the definition of idiopathic calcium nephrolithiasis; on the use of urinary tests of crystallization and of surgical observations during stone treatment in the management of these patients; on the identification of patients warranting preventive measures; on the role of fluid and nutritional measures and of drugs to prevent recurrent episodes of stones; and finally, on the cooperation between the urologist and nephrologist in the renal stone patients.

CONCLUSIONS

This document has addressed idiopathic calcium nephrolithiasis from the perspective of a disease that can associate with systemic disorders, emphasizing the interplay needed between urologists and nephrologists. It is complementary to the American Urological Association and European Association of Urology guidelines. Future areas for research are identified.

Obesity and urolithiasis: evidence of regional influences

There is evidence that obese patients have an increased risk of renal stone formation, although this relationship could be less evident in some populations. The aim of this study was to evaluate the impact of overweight and obesity on the risk of renal stone formation in a population consuming a Mediterranean diet and to better elucidate the mechanisms underlying the increased risk of urolithiasis observed in obese subjects. We performed a retrospective review of 1698 stone forming patients (mean age 45.9 ± 14.6 years; 984/714 M/F), attending outpatient stone clinics in Milan and Florence, seen between January 1986 and June 2014. Records were reviewed and data collected pertaining to age, gender, weight, height, stone composition, association with diabetes type 2 or gout and metabolic profile of 24-h urine to perform a descriptive study. We estimated prevalence ratios for body mass index (BMI) categories (underweight: BMI <18.5, normal: BMI 18.5-24.9, overweight: BMI 25-29.9 and obese ≥30). Overweight and obesity were present in 40.7 and 8 % of the men and in 19.9 and 8.7 % of the women in the study population. The mean BMI of patients with urolithiasis was found to be 24.5 ± 7.5 kg/m². BMI values were positively correlated with age (p = 0.000) and mean BMI was higher in males than in females (25.5 ± 8.9 vs 23.2 ± 4.4 kg/m²). In males, rates of overweight and obesity in renal stone formers were higher than the rates reported in the Italian general population in 2004 only for the age group 25-44 years, whereas males in all the other age groups and in females the rates of overweight and obesity in renal stone formers were similar to rates reported in the Italian general population. The rates of overweight and obesity were significantly different in patients with different chemical stone composition. In particular, patients with uric acid stones have rates of overweight and obesity higher than patients with calcium stones or other types of calculi. Also the rates of type 2 diabetes and gout were greater in patients with overweight and obesity. In overweight and obese patients, the urinary excretion of risk factors for stone formation, such as calcium, oxalate and urate, and also of inhibitory substances, such as citrate, were significantly higher than in patients with normal weight or underweight. The prevalence of overweight and obesity in patients with urinary calculi from a country consuming a Mediterranean diet is not higher than in the general population. It should be taken into account that not all the dietary patterns that are associated with obesity may involve a parallel increase in the risk of forming kidney stones and that epidemiological findings from one country could not be confirmed in other countries with different climatic, socioeconomic and cultural features.

Diet-induced acidosis and alkali supplementation

Western diet, high in protein-rich foods and poor in vegetables, is likely to be responsible for the development of a moderate acid excess leading to metabolism deregulation and the onset or worsening of chronic disturbances. Available findings seem to suggest that diets with high protein/vegetables ratio are likely to induce the development of calcium lithiasis, especially in predisposed subjects. Moreover, some evidence supports the hypothesis of bone metabolism worsening and enhanced bone loss following acid-genic diet consumption although available literature seems to lack direct and conclusive evidence demonstrating pathological bone loss. According to other evidences, diet-induced acidosis is likely to induce or accelerate muscle wasting or sarcopenia, especially among elderlies. Furthermore, recent epidemiological findings highlight a specific role of dietary acid load in glucose metabolism deregulation and insulin resistance. The aim of this review is to investigate the role of acid-genic diets in the development of the mentioned metabolic disorders focusing on the possible clinical improvements exerted by alkali supplementation.

Recent advances in managing and understanding nephrolithiasis/nephrocalcinosis

Urinary stone disease is a very common disease whose prevalence is still increasing. Stone formation is frequently associated with other diseases of affluence such as hypertension, osteoporosis, cardiovascular disease, metabolic syndrome, and insulin resistance. The increasing concentration of lithogenic solutes along the different segments of the nephron involves supersaturation conditions leading to the formation, growth, and aggregation of crystals. Crystalline aggregates can grow free in the tubular lumen or coated on the wall of the renal tubule. Plugs of crystalline material have been highlighted in the tubular lumen in some patients, but crystalline growth starting from plaques of calcium phosphate within the renal papillae has been demonstrated in others. Urinary supersaturation is the result of a complex interaction between predisposing genetic features and environmental factors. Dietary intake is certainly the most important environmental risk factor. In particular, an insufficient intake of dietary calcium (<600 mg/day) can increase the intestinal absorption of oxalate and the risk of calcium oxalate stone formation. Other possible risk factors that have been identified include excessive intake of salt and proteins. The potential role of dietary acid load seems to play an important role in causing a state of subclinical chronic acidosis; therefore, the intake of vegetables is encouraged in stone-forming patients. Consumption of sugar-sweetened soda and punch is associated with a higher risk of stone formation, whereas consumption of coffee, tea, beer, wine, and orange juice is associated with a lower risk. A high fluid intake is widely recognized as the cornerstone of prevention of all forms of stones. The effectiveness of protein and salt restriction has been evaluated in some studies that still do not allow definitive conclusions to be made. Calcium stone formation can be prevented by the use of different drugs with different mechanisms of action (thiazide diuretics, allopurinol, and potassium citrate), but there is no ideal drug that is both risk free and well tolerated.

Hyperoxaluria and Genitourinary Disorders in Children Ingesting Almond Milk Products

We describe 3 children presenting with hematuria, dysuria or kidney stones, and hyperoxaluria believed to be related to ingestion of excessive amounts of almond milk products. Our investigation of the oxalate content of several popular plant-based milk substitutes indicates that almond milk products are a particularly rich source of dietary oxalate. All genitourinary and urinary metabolic disturbances resolved after discontinuation of almond milk ingestion. Therefore, pediatricians should be aware of this potential link.

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

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.

Fad diets and their effect on urinary stone formation

The influence of unhealthy dietary habits on urinary stone formation has been widely recognized in literature. Dietary advice is indeed the cornerstone prescription for prevention of nephrolithiasis as well. However, only a small amount of medical literature has addressed the influence of popular or fad diets, often self-prescribed for the management of obesity and overweight or for cultural beliefs, on the risk of kidney stones. Thereby in this paper we analyze the current knowledge on the effects of some popular diets on overall lithogenic risk. High-protein diets, like Dukan diet, raise some concerns, since animal proteins are able to increase urinary calcium and to decrease urinary citrate excretion, thus leading to a high overall lithogenic risk. Low-carbohydrate diets, like Atkins diet or zone diet, may have a protective role against kidney stone formation, but there are also evidences stating that this dietary approach may rise calciuria and decrease citraturia, since it is generally associated to a relatively high intake of animal proteins. Vegan diet can be harmful for urinary stone disease, especially for the risk of hyperuricemia and micronutrient deficiencies, even if only few studies have addressed this specific matter. On the other side, the benefits of a lacto-ovo-vegetarian diet on kidney stone prevention have been largely emphasized, provided that the intake of calcium and oxalate is balanced. Traditional Mediterranean diet should exert a protective effect on nephrolithiasis as well, even if specific studies have not been carried out yet. High phytate and antioxidant content of this diet have however demonstrated to be beneficial in preventing the formation of new or recurrent calculi. Anyway, at the current state of knowledge, the most effective dietary approach to prevent kidney stone disease is a mild animal protein restriction, a balanced intake of carbohydrates and fats and a high intake of fruit and vegetables. Other fundamental aspects, which are often neglected in fad diets, are a normal intake of milk and dairy products and salt restriction. All these nutritional aspects should be greatly taken into account when patients who are willing to undergo fad or commercial diets ask for dietary advice.

Potential renal acid load and the risk of renal stone formation in a case-control study

OBJECTIVE

The potential renal acid load (PRAL) in diet may have a key role in renal stone formation through its effect on calcium and citrate metabolism. We examined the association between calcium renal stone formation and the PRAL in a population-based case-control study.

METHODS

A group of 123 calcium renal stone formers was compared with an equal number of age- and sex-matched controls. Dietary history was obtained by 24-h recall. Odds ratios (ORs) and 95% confidence intervals (CI) were calculated across quartiles of dietary intakes of PRAL.

RESULTS

Compared with those in the lowest quartiles of PRAL, we found an increased risk of renal stone formation for those in the highest quartile (Q4 OR=2.51, 95% CI 1.218-5.172). Regarding individual food patterns, we found a significant protection for a high consumption of vegetables (two or more servings/day; OR=0.526, 95% CI 0.288-0.962).

CONCLUSIONS

A PRAL in diet and a reduced consumption of vegetables are associated with an increased risk of calcium renal stone formation. In renal stone formers consumption of plant foods should be encouraged in order to counterbalance the acid load derived from animal-derived foods.

Protein intake, calcium balance and health consequences

High-protein (HP) diets exert a hypercalciuric effect at constant levels of calcium intake, even though the effect may depend on the nature of the dietary protein. Lower urinary pH is also consistently observed for subjects consuming HP diets. The combination of these two effects was suspected to be associated with a dietary environment favorable for demineralization of the skeleton. However, increased calcium excretion due to HP diet does not seem to be linked to impaired calcium balance. In contrast, some data indicate that HP intakes induce an increase of intestinal calcium absorption. Moreover, no clinical data support the hypothesis of a detrimental effect of HP diet on bone health, except in a context of inadequate calcium supply. In addition, HP intake promotes bone growth and retards bone loss and low-protein diet is associated with higher risk of hip fractures. The increase of acid and calcium excretion due to HP diet is also accused of constituting a favorable environment for kidney stones and renal diseases. However, in healthy subjects, no damaging effect of HP diets on kidney has been found in either observational or interventional studies and it seems that HP diets might be deleterious only in patients with preexisting metabolic renal dysfunction. Thus, HP diet does not seem to lead to calcium bone loss, and the role of protein seems to be complex and probably dependent on other dietary factors and the presence of other nutrients in the diet.

Impact of dietary counseling on urinary stone risk parameters in recurrent stone formers

OBJECTIVES

The aim of this study was to investigate the current impact of dietary counseling on the risk for urolithiasis.

METHODS

A retrospective cohort study of the patients treated in our stone clinics from July 2007 to February 2009 was carried out. Patients' urinary risk factors for stone disease were evaluated with pre- and postintervention 24-hour urine collections. All patients received dietary recommendations from a registered dietician at each visit.

RESULTS

One hundred thirty-seven subjects were identified and managed initially with only dietary interventions to address their urinary stone risk parameters. Average follow-up for this group was 15.19 ± 13.7 months. Subjects showed significant changes in urine volume (71.1%, 1.68 ± 0.68 to 2.59 ± 0.80 L/day, p < 0.0001), urine sodium (58.1%, 229.68 ± 72.51 to 144.65 ± 52.70 mmol/day, p < 0.0001), urine calcium (43.8%, 314.33 ± 95.75 to 216.81 ± 80.90 mg/day, p < 0.0001), urinary uric acid (50%, 0.821 ± 0.210 to 0.622 ± 0.128 g/day, p < 0.0001), urinary citrate (50.7%, 583.19 ± 330.86 to 797.36 ± 412.31, p < 0.0001), and urine oxalate (55.5%, 46.28 ± 10.31 to 32.56 ± 9.02 mg/day, p < 0.0001). The supersaturation for calcium oxalate also decreased significantly from baseline (9.34-5.03, p < 0.0001).

CONCLUSION

Urolithiasis is a multifactorial disease requiring a multidisciplinary approach. Our results support the use of dietary counseling by a registered dietician in the management of urolithiasis.

History, epidemiology and regional diversities of urolithiasis

Archeological findings give profound evidence that humans have suffered from kidney and bladder stones for centuries. Bladder stones were more prevalent during older ages, but kidney stones became more prevalent during the past 100 years, at least in the more developed countries. Also, treatment options and conservative measures, as well as 'surgical' interventions have also been known for a long time. Our current preventive measures are definitively comparable to those of our predecessors. Stone removal, first lithotomy for bladder stones, followed by transurethral methods, was definitively painful and had severe side effects. Then, as now, the incidence of urolithiasis in a given population was dependent on the geographic area, racial distribution, socio-economic status and dietary habits. Changes in the latter factors during the past decades have affected the incidence and also the site and chemical composition of calculi, with calcium oxalate stones being now the most prevalent. Major differences in frequency of other constituents, particularly uric acid and struvite, reflect eating habits and infection risk factors specific to certain populations. Extensive epidemiological observations have emphasized the importance of nutritional factors in the pathogenesis of urolithiasis, and specific dietary advice is, nowadays, often the most appropriate for prevention and treatment of urolithiasis.

Diet-induced acidosis: is it real and clinically relevant?

The concept of diet-induced ‘acidosis’ as a cause of disease has been a subject of interest for more than a century. The present article reviews the history of our evolving understanding of physiological pH, the physiological support for the concept of ‘acidosis’, the causes of acidosis, how it is recognised, its short-term effects as well as the long-term clinical relevance of preventative measures, and the research support for normalisation of pH. Further, we suggest differentiation of the terms ‘acidosis’ and ‘acidaemia’ as a way to resolve the conflation of these topics which has led to confusion and controversy. The available research makes a compelling case that diet-induced acidosis, not diet-induced acidaemia, is a real phenomenon, and has a significant, clinical, long-term pathophysiological effect that should be recognised and potentially counterbalanced by dietary means.

Subchronic Urinary Bladder Effects of Muraglitazar in Male Rats1

Muraglitazar, a PPARalpha/gamma dual agonist, was dosed orally to rats once daily for 13 weeks to evaluate urinary and urothelial changes of potential relevance to urinary bladder tumorigenesis. Groups of 17 young or aged rats per sex were fed a normal or 1% NH4Cl-supplemented diet and were dosed with 0, 1, or 50 mg/kg muraglitazar. Lithogenic ions and sediment were profiled from freshly voided urine samples collected 24 h after dosing, and drug exposures were measured. Urinary citrate, oxalate, and epidermal growth factor (EGF) were assayed from 18-h urine collections. Urothelium was assessed by light microscopy, scanning electron microscopy, and BrdU and TUNEL immunohistochemistry. When fed a normal diet, urine pH was higher in males (above 6.5). Urine volume/body weight was greater in females. Urine soluble/total calcium and magnesium and phosphorus/creatinine ratios were lower in male rats fed a normal diet. Urine citrate levels were decreased and oxalate was increased in young male rats treated with 50 mg/kg muraglitazar compared to age/sex/diet-matched controls. No changes in urine sediment were detected 24 h after dosing. In young male rats treated with 50 mg/kg on normal diet, multifocal urothelial necrosis and proliferation were observed, whereas urothelial apoptosis and urine EGF levels were unchanged compared to age/sex/diet-matched controls. Urothelial necrosis and proliferation were not correlated to systemic or urinary drug exposures and were prevented by dietary acidification. These data suggest that muraglitazar-associated changes in urine composition predispose to urothelial cytotoxicity and proliferation in the urinary bladder of young male rats and that urine sediment must be profiled at multiple daily timepoints to fully qualify drug-induced changes in urine composition.