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

The complex relationship between vitamin D and kidney stones: balance, risks, and prevention strategies

The association between vitamin D and kidney stones is characterized by a remarkable multi-dimensional complexity involving numerous physiological and metabolic pathways. Vitamin D is pivotal in maintaining calcium-phosphorus metabolic homeostasis and bone health. However, fluctuations in its intake, whether excessive or insufficient, May potentially increase the risk of kidney stones. Vitamin D exerts its influence on kidney stone formation indirectly by increasing the efficiency of intestinal calcium absorption and regulating renal calcium excretion. Moreover, there is a robust correlation between various states of vitamin D, particularly its active form, 1,25-dihydroxyvitamin D, and the development of numerous kidney stones. This finding underscores the necessity of individualized medical treatment in vitamin D supplementation and kidney stone prevention. When developing treatment strategies, it is essential to consider the patient's genetic background, lifestyle, environmental factors, and overall health. To prevent the formation of kidney stones, it is recommended that patients adopt a comprehensive approach, which May include measures such as moderate sun exposure, dietary modification, moderate exercise, and weight management. These preventive measures are designed to maintain healthy calcium and phosphorus metabolism and reduce kidney stone formation risk. Future studies should aim to elucidate the detailed mechanisms of vitamin D metabolism, individual differences, and the role of genes in this process. Furthermore, the role of lifestyle interventions in preventing kidney stones requires greater attention. Moreover, the implementation of large-scale, long-term prospective studies and randomized controlled trials will facilitate the assessment of the actual effects of diverse vitamin D supplementation strategies, thereby providing a robust scientific foundation for advancing more precise prevention strategies and clinical guidelines.

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.

Kidney Stone Prevention

Kidney stone disease (KSD) (alternatively nephrolithiasis or urolithiasis) is a global health care problem that affects almost people in developed and developing countries. Its prevalence has been continuously increasing with a high recurrence rate after stone removal. Although effective therapeutic modalities are available, preventive strategies for both new and recurrent stones are required to reduce physical and financial burdens of KSD. To prevent kidney stone formation, its etiology and risk factors should be first considered. Low urine output and dehydration are the common risks of all stone types, whereas hypercalciuria, hyperoxaluria, and hypocitraturia are the major risks of calcium stones. In this article, up-to-date knowledge on strategies (nutrition-based mainly) to prevent KSD is provided. Important roles of fluid intake (2.5-3.0 L/d), diuresis (>2.0-2.5 L/d), lifestyle and habit modifications (for example, maintain normal body mass index, fluid compensation for working in high-temperature environment, and avoid cigarette smoking), and dietary management [for example, sufficient calcium at 1000-1200 mg/d, limit sodium at 2 or 3-5 g/d of sodium chloride (NaCl), limit oxalate-rich foods, avoid vitamin C and vitamin D supplements, limit animal proteins to 0.8-1.0 g/kg body weight/d but increase plant proteins in patients with calcium and uric acid stone and those with hyperuricosuria, increase proportion of citrus fruits, and consider lime powder supplementation] are summarized. Moreover, uses of natural bioactive products (for example, caffeine, epigallocatechin gallate, and diosmin), medications (for example, thiazides, alkaline citrate, other alkalinizing agents, and allopurinol), bacterial eradication, and probiotics are also discussed. Adv Nutr 2023;x:xx-xx.

Primary Contributors to Dietary Acid Load in Patients With Urolithiasis

OBJECTIVES

In susceptible individuals, high dietary acid load may contribute to the formation of certain types of kidney stones via lowering urine pH and citrate excretion. The objective of this study is to determine the contribution of dietary acid from food groups in people with urolithiasis.

DESIGN AND METHODS

Patients with calcium urolithiasis (n = 83) who completed food records were used for this retrospective analysis. Descriptive statistics were calculated for nutrients, potential renal acid load (PRAL), and estimated net endogenous acid production (NEAP_est). Pearson's correlations were calculated between PRAL and NEAP_est with each nutrient.

RESULTS

Data from a total of 83 patients were used. Average PRAL was positively correlated with energy (r = 0.260, P = .02), total protein (r = 0.463, P < .001), animal protein (r = 0.555, P < .001), total fat (P = .399, P < .001), sodium (r = 0.385, P < .001), and phosphorus (r = 0.345, P < .001) intake. PRAL was negatively correlated with fiber (r = -0.246, P = .03) intake. NEAP_est was positively correlated with total protein (r = 0.269, P = .01), animal protein (r = 0.377, P < .001), fat (r = 0.222, P = .04), and sodium (r = 0.250, P = .02) intake. NEAP_est was negatively correlated with fiber (r = -0.399, P < .001), potassium (r = -0.360, P < .001), and magnesium (r = -0.233, P = .03) intake. For PRAL, meat contributed the highest acid load (52.7%), followed by grains (19.6%) and combination foods (19.6%). Beverages contributed the greatest alkali load (35.1%), followed by vegetables (30.6%) and fruits (28.6%). For NEAP_est, cheese contributed the highest acid load (21.8%), followed by grains (19.3%) and meat (18.1%).

CONCLUSIONS

For individuals with urolithiasis promoted by acidic urine and/or low urine citrate, dietary patterns with a high dietary acid load may contribute to recurrence risk. Meat and grains were the major contributors to dietary acid load in this cohort of patients with a history of kidney stones, whereas beverages, fruits, and vegetables contributed net alkali.

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.

Calcium and Vitamin D Supplementation and Their Association with Kidney Stone Disease: A Narrative Review

Kidney stone disease is a multifactorial condition influenced by both genetic predisposition and environmental factors such as lifestyle and dietary habits. Although different monogenic polymorphisms have been proposed as playing a causal role for calcium nephrolithiasis, the prevalence of these mutations in the general population and their complete pathogenetic pathway is yet to be determined. General dietary advice for kidney stone formers includes elevated fluid intake, dietary restriction of sodium and animal proteins, avoidance of a low calcium diet, maintenance of a normal body mass index, and elevated intake of vegetables and fibers. Thus, balanced calcium consumption protects against the risk for kidney stones by reducing intestinal oxalate availability and its urinary excretion. However, calcium supplementation given between meals might increase urinary calcium excretion without the beneficial effect on oxalate. In kidney stone formers, circulating active vitamin D has been found to be increased, whereas higher plasma 25-hydroxycholecalciferol seems to be present only in hypercalciuric patients. The association between nutritional vitamin D supplements and the risk for stone formation is currently not completely understood. However, taken together, available evidence might suggest that vitamin D administration worsens the risk for stone formation in patients predisposed to hypercalciuria. In this review, we analyzed and discussed available literature on the effect of calcium and vitamin D supplementation on the risk for kidney stone formation.

Dietary Acid Load Is Positively Associated with the Incidence of Hyperuricemia in Middle-Aged and Older Korean Adults: Findings from the Korean Genome and Epidemiology Study

Hyperuricemia has been associated with a number of chronic diseases, such as type 2 diabetes mellitus, hypertension, and cardiovascular diseases. Dietary acid load plays a key role in regulating uric acid levels. We hypothesized that potential renal acid load (PRAL) and net endogenous acid production (NEAP) score would be positively associated with the incidence of hyperuricemia. Data from the Health Examinees study, a part of the Korean Genome and Epidemiology Study were used. The PRAL and NEAP scores were calculated to evaluate the dietary acid load. Hyperuricemia was defined as follows: >7.0 mg/dL and >6.0 mg/dL of serum uric acid levels in men and women, respectively. Multivariable Cox proportional hazard models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the incidence of hyperuricemia. We identified 2500 new cases of hyperuricemia during a mean follow-up of 5.0 years (223,552 person years). The participants in the highest quartiles of the PRAL and NEAP score had 21% (HR: 1.21, 95% CI: 1.07–1.35, p for trend <0.0001) and 17% (HR: 1.17, 95% CI: 1.04–1.31, p for trend <0.0001) higher risks for hyperuricemia, respectively, than those in the lowest quartiles, after adjusting for covariates. In this prospective cohort study, a higher dietary acid load was positively associated with a higher incidence of hyperuricemia in Korean adults. This suggests that an alkaline diet may be an effective strategy to reduce the future risk of elevated uric acid levels.

Distal renal tubular acidosis: a systematic approach from diagnosis to treatment

Renal tubular acidosis (RTA) comprises a group of disorders in which excretion of hydrogen ions or reabsorption of filtered HCO₃ is impaired, leading to chronic metabolic acidosis with normal anion gap. In the current review, the focus is placed on the most common type of RTA, Type 1 RTA or Distal RTA (dRTA), which is a rare chronic genetic disorder characterized by an inability of the distal nephron to secrete hydrogen ions in the presence of metabolic acidosis. Over the years, knowledge of the molecular mechanisms behind acid secretion has improved, thereby greatly helping the diagnosis of dRTA. The primary or inherited form of dRTA is mostly diagnosed in infancy, childhood, or young adulthood, while the acquired secondary form, as a consequence of other disorders or medications, can happen at any age, although it is more commonly seen in adults. dRTA is not as “benign” as previously assumed, and can have several, highly variable long-term consequences. The present review indeed reports and summarizes both clinical symptoms and diagnosis, long-term outcomes, genetic inheritance, epidemiology and current treatment options, with the aim of shedding more light onto this rare disorder. Being a chronic condition, dRTA also deserves attention in the transition between pediatric and adult nephrology care, and as a rare disease it has a place in the European and Italian rare nephrological diseases network.

Dietary Acid Load and Cardiometabolic Risk Factors-A Narrative Review

The Western, diet rich in acidogenic foods (e.g., meat, fish and cheese) and low in alkaline foods (e.g., vegetables, fruits and legumes), is deemed to be a cause of endogenous acid production and elevated dietary acid load (DAL), which is a potential cause of metabolic acidosis. Multiple authors have suggested that such a dietary pattern increases the excretion of calcium and magnesium, as well as cortisol secretion. In addition, it is associated with decreased citrate excretion. All of these seem to increase blood pressure and insulin resistance and may contribute to the development of cardiometabolic disorders. However, there are inconsistencies in the results of the studies conducted. Therefore, this narrative literature review aims to present the outcomes of studies performed in recent years that investigated the association between DAL and the following cardiometabolic risk factors: blood pressure, hypertension, carbohydrate metabolism and lipid profile. Study outcomes are divided into (i) statistically significant positive association, (ii) statistically significant inverse association, and (iii) no statistically significant association.

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.

Anthropometric variables, physical activity and dietary intakes of patients with uric acid nephrolithiasis

To evaluate anthropometric variables, energy expenditure by physical activity and nutrient intake of uric acid stone formers (UA-RSFs) compared to non-forming subjects (C). The study included 33 consecutive male patients with a diagnosis of "pure" stones of anhydrous uric acid at infrared spectroscopy and 49 male control subjects with no history of urinary stones. A personal interview was conducted including questionnaires for physical activity and dietary intakes. Anthropometric parametric and blood pressure were measured. Mean age, weight, height, waist circumference, body mass index, systolic and diastolic blood pressure values, dietary energy, carbohydrate intake, lipid intake, dietary acid load, time spent for different physical activities and total energy expenditure for physical activity were not different in UA-RSFs with respect to C. Mean dietary protein (76.2 ± 19.6 vs 65.4 ± 14.7 g/day, P = 0.006) and ethanol intake (10.4 ± 8.8 vs 4.1 ± 8.6, P = 0.002) were higher in UA-RSFs than in C. History of renal disease, heart disease and treatment with thiazides or allopurinol were more frequent and mean serum glucose and triglycerides (104 ± 12 vs 97 ± 11 mg/dl, P = 0.043) (172 ± 77 vs 123 ± 52 mg/dl, P = 0.023) were higher in UA-RSFs. Metabolic syndrome was more frequent in UA-RSFs (57% vs 39%) but not significant (p = 0.09). Increased dietary animal protein (and ethanol) intake can act as co-factors for uric acid stone formation although a more complex and not fully elucidated metabolic background can have an even more crucial role in the pathogenesis of this disease even in the absence of overweight.

Dietary Acid Load: mechanisms and evidence of its health repercussions

Diet composition has long been known to influence acid-base balance by providing acid or base precursors. In general, foods rich in protein, such as meat, cheese, eggs, and others, increase the production of acid in the body, whereas fruit and vegetables increase alkalis. The capacity of acid or base production of any food is called potential renal acid load (PRAL). Diets high in PRAL induce a low-grade metabolic acidosis state, which is associated with the development of metabolic alterations such as insulin resistance, diabetes, hypertension, chronic kidney disease, bone disorders, low muscle mass and other complications. The aim of this paper is to review the available evidence which evaluates the association of the PRAL of the diet with the incidence of chronic diseases and metabolic disorders, as well as related mechanisms involved in their development.

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.

Preventive Kidney Stones: Continue Medical Education

Nephrolithiasis is a common health problem across the globe with a prevalence of 15%-20%. Idiopathic hypercalciuria is the most common cause of nephrolithiasis, and calcium oxalate stones are the most common type of stones in idiopathic hypercalciuric patients. Calcium phosphate stones are frequently associated with other diseases such as renal tubular acidosis type 1, urinary tract infections, and hyperparathyroidism. Compared with flat abdominal film and renal sonography, a noncontrast helical computed tomography scan of the abdomen is the diagnostic procedure of choice for detection of small and radiolucent kidney stones with sensitivity and specificity of nearly 100%. Stones smaller than 5 mm in diameter often pass the urinary tract system and rarely require surgical interventions. The main risk factors for stone formation are low urine output, high urinary concentrations of calcium, oxalate, phosphate, and uric acid compounded by a lower excretion of magnesium and citrate. A complete metabolic workup to identify the risk factors is highly recommended in patients who have passed multiple kidney stones or those with recurrent disease. Calcium oxalate and calcium phosphate stones are treated by the use of thiazide diuretics, allopurinol, and potassium citrate. Strategies to prevent kidney stone recurrence should include the elimination of the identified risk factors and a dietary regimen low in salt and protein, rich in calcium and magnesium which is coupled with adequate fluid intake.

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.

Dietary Protein and Potassium, Diet-Dependent Net Acid Load, and Risk of Incident Kidney Stones

BACKGROUND AND OBJECTIVES

Protein and potassium intake and the resulting diet-dependent net acid load may affect kidney stone formation. It is not known whether protein type or net acid load is associated with risk of kidney stones.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We prospectively examined intakes of protein (dairy, nondairy animal, and vegetable), potassium, and animal protein-to-potassium ratio (an estimate of net acid load) and risk of incident kidney stones in the Health Professionals Follow-Up Study (n=42,919), the Nurses' Health Study I (n=60,128), and the Nurses' Health Study II (n=90,629). Multivariable models were adjusted for age, body mass index, diet, and other factors. We also analyzed cross-sectional associations with 24-hour urine (n=6129).

RESULTS

During 3,108,264 person-years of follow-up, there were 6308 incident kidney stones. Dairy protein was associated with lower risk in the Nurses' Health Study II (hazard ratio for highest versus lowest quintile, 0.84; 95% confidence interval, 0.73 to 0.96; P value for trend <0.01). The hazard ratios for nondairy animal protein were 1.15 (95% confidence interval, 0.97 to 1.36; P value for trend =0.04) in the Health Professionals Follow-Up Study and 1.20 (95% confidence interval, 0.99 to 1.46; P value for trend =0.06) in the Nurses' Health Study I. Potassium intake was associated with lower risk in all three cohorts (hazard ratios from 0.44 [95% confidence interval, 0.36 to 0.53] to 0.67 [95% confidence interval, 0.57 to 0.78]; P values for trend <0.001). Animal protein-to-potassium ratio was associated with higher risk (P value for trend =0.004), even after adjustment for animal protein and potassium. Higher dietary potassium was associated with higher urine citrate, pH, and volume (P values for trend <0.002).

CONCLUSIONS

Kidney stone risk may vary by protein type. Diets high in potassium or with a relative abundance of potassium compared with animal protein could represent a means of stone prevention.

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.

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.

Dietary recommendations and treatment of patients with recurrent idiopathic calcium stone disease

This review describes the various dietary regimens that have been used to advise patients on how to prevent the recurrence of their calcium-containing kidney stones. The conclusion is that although there is some general advice that may be useful to many patients, it is more efficacious to screen each patient individually to identify his/her main urinary, metabolic, nutritional, environmental, and lifestyle risk factors for stone-formation and then tailor specific advice for that particular patient based on the findings from these investigations. If the patient can be motivated to adhere strictly to this conservative approach to the prophylactic management of their stone problem over a long time period, then it is possible to prevent them from forming further stones. This approach to stone management is considerably less expensive than any of the procedures currently available for stone removal or disintegration. In the UK, for each new stone episode prevented by this conservative approach to prophylaxis it is calculated to save the Health Authority concerned around £2000 for every patient treated successfully. In the long term, this accumulates to a major saving within each hospital budget if most stone patients can be prevented from forming further stones and when the savings are totalled up country-wide saves the National Exchequer considerable sums in unclaimed Sick Pay and industry a significant number of manpower days which would otherwise be lost from work. It is also of immense relief and benefit to the patients not to have to suffer the discomfort and inconvenience of further stone episodes.

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.

High-protein diets and renal health

High-protein diets (i.e., protein content of more than 25% of energy or more than 2 g/kg body weight per day) based on meat and dairy products are repeatedly promoted for weight reduction and better health, but the evidence supporting these notions is quite dubious. As described in the present review, there is a reason to be concerned about adverse effects of such diets, including glomerular hyperfiltration, hypertensive effects of a concomitant increase in dietary sodium, and an increased risk of nephrolithiasis. These diet-induced physiological consequences might lead to an increase in the prevalence of chronic kidney disease in the general population without preexisting kidney disease. Accordingly, we find medical reasons to refrain from promoting high-protein diets, in particular those based on meat and dairy products, until clear-cut evidence for the safety and for the superiority of such diets on human health has been provided.