Over the past 20 years, the concepts of medical treatment and prevention of nephrolithiasis have changed considerably. They are based on a systematic and essential etiological investigation for each stone patient. It includes the analysis of the calculation and the search for lithogenic risk factors based on clinical, radiological and biological data. The nature of stones has completely changed over the past 100 years with today a predominance of oxalocalcic lithiasis. It is the changes in eating habits that explain the modifications in the nature of the stones. The dietary investigation thus represents an important moment in the etiological investigation and the implementation of hygienic-dietary rules is essential to prevent the risk of stone recurrence.
Eating habits: The dietary survey must provide information on habits present several months before the discovery of the stones. The survey must be based on reference questionnaires. The data from this survey are essential because dietary imbalances or excesses and even more so lack of drinking constitute the main factors in primary calcium lithiasis. Nature and type of drinks:
Drinks: The absorption of abundant drinks so as to dilute the urine and bring it below the threshold for crystallization of calcium salts is a fundamental principle in the prevention of recurrent urolithiasis. It is not always easy for patients to know how much drinking water they can consume; many of them are unaware of the qualities or defects of tap water or the difference between spring water and mineral water. Likewise, urologists, who are poorly informed, most often stick to general advice (“drink a lot”), avoiding going into too much detail. However, a few simple rules, combined with a minimum knowledge of the different waters, make it possible to provide effective advice.
There are different categories of water:
Mineral waters Not all bottled waters are mineral. Mineral waters are waters which can boast properties favorable to health, benefiting from an original nature and purity, coming from groundwater protected from any pollution, stable in their composition.
For some, their high concentration of mineral substances gives them properties that may be beneficial to health, which they can take advantage of, like real “medicines”. Exclusive consumption of these waters can cause problems due to poorly balanced mineralization (diarrhea, etc.).
Pre-packaged spring water: This is groundwater protected from any pollution, suitable for human consumption without treatment or addition, and meeting quality requirements. Spring water is distinguished from natural mineral water by the fact that it meets drinking standards and that there is no imbalance in the concentration of its minerals. It is not required to have a constant and characteristic mineral composition and it cannot therefore claim to have beneficial effects for health. Public water supply This is either groundwater coming from a source or borehole, or surface water coming from direct pumping into rivers, canals, lakes and ponds.
This water from the distribution network can be chemically treated (example: chlorination) but must then meet various parameters which define the drinking standards. The composition of tap water is available and displayed at the town hall and at the DDASS [6].
What daily diuresis? In the case of common calcium lithiasis, the universal consensus is to maintain a daily diuresis of at least two liters per 24 hours. Drinks must be well distributed during the nycthemerus with, in particular, an abundant intake of drinks at bedtime and, in severe forms, a new drink every time you get up at night. Indeed, the absence of sufficient dilution of urine emitted during the night, reflected by a high density of urine upon awakening, is a frequent cause of recurrence of stone even though the volume of 24-hour diuresis is satisfactory.
It is therefore important to control, in addition to the volume of 24-hour urine, the density of morning urine. What type of drink should you recommend?
Recent epidemiological studies have shown that the optimal calcium intake in patients with calcium lithiasis is 800 to 1000 mg/day. Meat, vegetables and fruits, that is to say all non-dairy products, provide around 200 mg/day of calcium. It therefore remains to ensure an intake of 600 to 800 mg of calcium per day in the form of drinking water and dairy products. The distribution between drinking water and dairy products must take into account the patient’s tastes and habits. Indeed, the calcium content of drinking water available in France varies from 5 mg/l for the poorest to 600 mg/l for the richest. Likewise, the calcium content of dairy products varies from 120 mg/100 g for the less rich (whole or semi-skimmed milk, Brie or fresh goat’s cheese) to 1200 mg/100 g for the richest (Emmental or Parmesan).
In a patient preferring water very low in calcium, an intake of at least 600 to 800 mg of calcium per day must be provided in the form of dairy products, at the patient’s choice. Likewise, for a patient who loves cheese, we recommend drinking water low in calcium. Conversely, in a patient who does not like dairy products, water richer in calcium is recommended to ensure sufficient calcium intake. Explain to the patient to check the labels on the bottles.
Calcium: An excess of calcium in 24-hour urine (hypercalciuria) is found in 25 to 60% of calcium stone patients depending on the series. In the genesis of this hypercalciuria we find: • nutritional factors on which the therapist can intervene; • non-nutritional factors (genetic, physiological, etc.). Three nutrients influence calciuria flow: • calcium intake (++); • sodium intake (+); • protein intake (+++++).
Reminders on Calcium Metabolism Calcium: Inputs The only calcium input is through food. The average intake in adults is 25 mmol/day (i.e. 1 g). Milk, dairy products and drinking water are the main sources of dietary calcium. Meats, fruits and green vegetables are low in calcium. Calcium found in foods other than dairy and water is unlikely to be absorbed. Digestive absorption represents 20% of the quantity ingested (if this is normal), or 5 mmol/day (200 mg). Calcium outlets The kidney is the only possible outlet for calcium. At equilibrium, renal losses equal net digestive absorption, i.e. 5 mmol/d. Expressed in relation to body weight, calciuria is less than 0.1 mmol/kg per day regardless of sex. There are significant variations in calciuria even in healthy subjects with a non-Gaussian distribution of values which range from 1.5 to 12.8 mmol/d. Approximately 10% of healthy subjects have a calciuria greater than 0.1 mmol/kg per day
Finally, the way calcium is consumed is important: calcium supplements consumed outside of meals increase the risk of lithiasis, unlike calcium taken during meals. Other nutritional factors that can influence calciuria Salt intake There is a relationship between natriuresis (amount of salt in urine) and calciuria. The greater the dietary sodium intake, the higher the urinary excretion of sodium and the higher the calciuria.
Thus, patients are hypercalciuric for a sodium intake of 200 mmol/d (> 13 g/d) and are no longer so if the intake is reduced to 100 mmol/d. Influence of protein intake (++++) We have long known that the consumption of proteins (animal: meat, fish, poultry, eggs) is associated with an increased incidence of calcium urolithiasis. There is a relationship between protein intake and calciuria. The higher the protein intake, the higher the calciuria in both men and women. Influence of carbohydrate intake in rapidly absorbed sugars, obesity and alcohol Fast sugars, obesity and alcohol lead to insulin resistance. However, insulin reduces tubular reabsorption of calcium. Consumption of fast sugars is associated with an increased risk of lithiasis.
Fibers could influence calciuria but the data in the literature do not allow us to assess its importance. In total, calciuria is very influenced by diet, especially with regard to proteins, salt and calcium. For a long time, calcium lithiasis patients were prescribed diets low in calcium (400 mg/day, which excluded all diary products). These diets turned out to be harmful with worsening of the stone disease (increase in oxaluria) and bone demineralization while calciuria fell variably (compliance problem, etc.).
Today we advise lithiasis patients to consume calcium: “Neither too much nor too little”: which corresponds to a daily intake of two or three dairy products. Hyperoxaluria Hyperoxaluria is proportionally more important than hypercalciuria in increasing urine saturation but it is rare in general stone patients.
Oxalate is a terminal acid of metabolism whose only route of excretion is the kidney. Oxalate binds to calcium to form a lithogenic complex: calcium oxalate. Oxalate inputs Food: cocoa, tea, certain vegetables and red berries, dietary fiber.
This oxalate input corresponds to 10 to 20% of urinary oxalate. In fact, the quantity of oxalate ingested varies greatly from one day to the next (100—1000 mg) and its absorption is also very variable. Oxalate in the digestive tract must be in free form to be absorbed. This free fraction is very dependent on the calcium content of the food bolus (+++). In fact, calcium complexes oxalate and blocks its absorption. Calcium intake is perhaps the most influential nutritional component on oxaluria. However, it has been shown that a diet very low in oxalate can reduce urinary oxalate excretion by half.
Eighty to 90% of oxalate comes from intermediate metabolism: hepatic oxalate synthesis which depends on lean mass (correlation between body surface area and oxaluria). This synthesis is dependent on an enzyme: alanine-glyoxylate aminotransferase (deficient in primary hyperoxaluria type I). Oxalate exits urine. Hyperuricuria Hyperuricuria (excess uric acid in the urine) is a metabolic risk factor for calcium lithiasis because uric acid promotes oxalocalcium crystallization.
Hyperuricuria can have two origins: • diet, in particular the intake of meat proteins (animal proteins) and offal which are rich in glutamine, a precursor of uric acid; • endogenous overproduction (=gout) or excess renal elimination. Hypocitraturia Citrate is a small, ubiquitous organic acid that constitutes a source of energy for cells. Citrate comes from glucose metabolism. The citrate is filtered by the glomerulus then a large part is reabsorbed by the tubular cells. Citrate in urine has the property of inhibiting the formation and aggregation of calcium oxalate crystals. In the event of hypocitraturia, the risk of oxalocalcium stone formation is increased. Salt intake reduces citraturia. Low diuresis leads to hypocitraturia. Alkalizing diets (vegetarian type) increase citraturia while diets rich in meat proteins (which provide acids) do the opposite.
Diets rich in dietary fiber or potassium (which include a high intake of fruits and vegetables) increase citraturia. The contributing causes of idiopathic hypocitraturia are therefore: • low urinary volume; • excessive salt consumption; • excessive protein consumption; • low consumption of fruits and vegetables. Finally, citrus fruits (lemon, orange) provide citrate. Taking a 200 ml glass of orange juice is recommended in cases of oxalocalcic lithiasis.
Conclusions Highlighting the risk factors for renal lithiasis makes it possible to implement “dietary readjustment” measures (see the appendix for the advice sheet to be given to patients and downloadable from the “Urofrance.org” website) and, if necessary, a medical treatment. Finally, the successes achieved by extracorporeal lithotripsy and endourology should not make us forget that the prevention of renal lithiasis is the best weapon against recurrence.
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