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Diet for patients with kidney stones – fundamental nutritional guidelines
Table of Contents
1. Kidney stones – everything you need to know
Kidney stones are a chronic systemic condition characterized by the presence of insoluble deposits in the urinary system in the form of stones or salt crystals. These are the result of precipitation of chemical substances in the urine (when the concentration of compounds exceeds a certain level of solubility in the body). Stones can form in any part of the urinary system, be single or multiple, and accumulate on one or both sides in the kidneys (most commonly the renal pelvis), ureters, and bladder. They are typically composed of calcium (71%), potassium (26%), and phosphorus (7%). Kidney stones affect 1-2% of the population, most commonly between the ages of 20 and 40. Among patients, there are twice as many men as women, which may be due to more frequent obesity and poorer dietary habits in men.2. Causes leading to the formation of kidney stones
There are many factors that can contribute to the development of kidney stones, and some of the most common ones include: not enough fluids in the diet or too much of it (e.g. during intense physical activity in hot conditions), insufficient pH in urine (< 5.5 and > 7), which decreases the solubility of certain substances, high relative density of urine, inadequate diet (too much protein, sodium, high in saliva), deficiency of compounds that restrict the crystallization of phosphorus compounds, such as magnesium and citrates, obesity and overweight, long-term immobility, frequent and chronic infections of the urinary system, the presence of other diseases such as osteoporosis, uric acid stones, hyperthyroidism, hyperparathyroidism, diabetes, metabolic syndrome, congenital metabolic disorders such as adenine phosphoribosyltransferase deficiency, xanthine oxidase deficiency, orotic aciduria type I, alkaptonuria, and genetic predisposition (M. Grzymisławski 2019; H. Ciborowska, A. Rudnicka 2014).3. Indications of kidney stones
In the case of kidney stones, the most common indications are: severe pain in the lumbar region, known as renal colic, nausea, vomiting, excessive sweating, pale skin, fever, restlessness, frequent urination in small amounts, anuria (when the stones completely block the urine flow), hematuria, constipation and bloating, urinary retention, pyelonephritis (M. Grzymisławski 2019; H. Ciborowska, A. Rudnicka, 2014).4. Dietary recommendations for limestone and calcium stones
This type of stones develops when there is excessive consumption of citric acid or acid in the urine, after an operation to remove part of the intestine, in cases of inflammatory bowel disease, excessive intake of vitamin C, insufficient intake of vitamin B6, and impaired excretion of hydrogen ions by the kidneys. In the presence of limestone and calcium stones, it is recommended to limit salt and products with added salt. If the stone is formed as a result of excessive excretion of calcium, for example, in hyperthyroidism or osteoporosis, it is not recommended to reduce calcium intake in the diet. It is also recommended to drink at least 2 liters of fluid per day. Limiting the consumption of animal protein is also important. Increasing the intake of vitamin B6 can help reduce the risk of this type of stones. It is possible to distinguish recommended, allowed in limited quantities, and prohibited products. Prohibited products include: spinach, sorrel, rhubarb, strong teas, coffee, cocoa, dried figs, chocolate, meat preserves, fish preserves, pickles, and soup concentrates. In limited quantities, the consumption of milk and milk products, legumes, potatoes, carrots, beets, peas, tomatoes, green and cabbage vegetables, plums, gooseberries, nuts, and sugar is allowed. However, it is recommended to consume large quantities of fluids, fruit juices, citrus fruits, whole-grain cereal products, cucumbers, onions, and corn.5. Nutritional recommendations for phosphate and calcium stones
In this particular case, the stone is composed of phosphate and calcium, which is produced in the alkaline urine often as a result of bacterial infection. Dietary treatment should aim to limit the supply of salt and products rich in phosphorus, calcium and starch (e.g. milk, eggs, legume seeds, cottage cheese). The products that are contraindicated in phosphate and calcium stones include: alkaline mineral waters (ph > 7), legume seeds, spinach, juice, potatoes, raspberry, mackerel, pepper, starch, cocoa, strong tea, coffee, salt, salty dishes, and spices with sodium glutamate. Limited intake of: potatoes, other vegetables, fruits, milk, eggs is allowed. Recommended products include: high fluid intake, meat, fish, bread, coarse grains, pasta, butter, honey, fruit juices and citrus fruits.6. Nutritional recommendations for uric acid stones
The cause of uric acid stones is a diet rich in purines (meat, fish, mushrooms), excessive concentration of uric acid in the urine, and pH < 5.3. The crystals are formed from uric acid, which is the end product of metabolism, normally dissolved and excreted by the kidneys. The disease that promotes this type of stone is hyperuricemia, which consists of excessive accumulation of uric acid in the blood and is deposited in the muscles and joints. The diet should be based on the alkalinization of urine, as uric acid dissolves in an alkaline medium and is distributed in the milk and milk product world. In case of uric acid stones, a diet rich in milk and milk products is recommended. Products not recommended are: offal, lamb, pork, herring, sardines, sprat, caviar, chocolate, cocoa, strong tea and coffee, meat and fish broths, legumes and mushrooms. Limited amounts of other types of meat (100-150 g per day), cooked poultry, fish, and cereal products are allowed. Among the recommended products are large amounts of fluids, mineral water, fruits and vegetables (especially lemons), milk, low-fat cottage cheese, honey, and sugar.7. Nutritional recommendations for cases of phosphate, magnesium, and ammonium stones
The components that form phosphorus-magnesium-ammonium stones are often the result of bacterial infections of the urinary system. Due to the higher prevalence of these infections among women, they are more commonly affected by this type of stones. The diet in this case consists of limiting the intake of phosphates found in maturing cheese, egg yolks, milk and its derivatives, meat products, fish, canned food, cereal products with coarser grains, dried seeds from legumes, cocoa, chocolate, and nuts. Similarly to other types of stones, it is advisable to increase fluid intake. In cases of low citrate and magnesium levels in urine, it is recommended to increase the consumption of citrus fruits and juices, as well as magnesium-rich products such as corn, sunflower seeds, leafy green vegetables, and bananas.8. Nutritional recommendations for cystine concretions
In the case of cystine concretions, it is important to reduce the intake of sulphur amino acid cysteine. Cystine concretions occur in approximately 1-2% of cases. These concretions can reach significant sizes and fill the renal pelvis. This type of concretions is present in patients with cystinuria, a congenital disorder affecting the re-absorption of amino acids, including cysteine, ornithine, arginine, and lysine. Cystine is found in high amounts in dairy products. Dietary therapy for cystine concretions involves increasing fluid intake to over 3 liters per day, which is best achieved by doubling the recommended daily intake for the body. It is also recommended to increase the intake of vitamin B6, whose rich sources are yeast, legumes, cooked beef, pork, veal, poultry meat, fish, bell peppers, Brussels sprouts, cabbage, carrot, spinach, potatoes, whole-grain bread, powdered milk, eggs, cow milk, bananas, oranges, and apples.9. Dietary suggestions for xanthine stones
This type of kidney stone is a result of excessively high concentrations of the insoluble purine compound, xanthine, in the urine. Xanthinuria is a disease caused by a deficiency of xanthine oxidase, which leads to a lack of conversion of xanthine to uric acid. Dietary therapy in this case involves a low-purine diet, limiting the consumption of meat, fish, and mushrooms, as well as a high intake of fluids and products that alkalize the urine. The milk-rice diet is particularly recommended.10. General nutritional recommendations overview
Regardless of the type of stones and other individual factors, a very important role is played in preventing kidney stones from forming. To minimize the risk of recurrence and formation of kidney stones, a sufficient amount of fluid over 2 l/ day should be taken. It is also important to limit the intake of table salt (< 5 g/day) and products containing oxalic acid. To reduce the risk of recurrence and formation of kidney stones, it is recommended to limit the intake of simple sugars. It is also often recommended to limit the intake of animal protein. An increased intake of omega-3 fatty acids is recommended due to their ability to lower calcium and oxalate levels. In case of low fish intake, supplementation with fish oil or oil from algae such as Schizochytrium sp., Crypthecodinium Cohnii or Ulkenia sp. should be considered. If obesity or overweight coexist, it is recommended to aim for weight loss and increased physical activity. It is important to include a large amount of vegetables and fruits in the diet due to their high content of potassium, magnesium and alkalinizing effect. A good option is the DASH diet, which is rich in vegetables, fruits, low in animal protein and contains a moderate amount of low-fat dairy products. An appropriately composed diet and lifestyle modification are the basic elements in the prevention and treatment of kidney stones.
