Kidney stones: is diet an important factor?
The importance of the diet for kidney stones is quite relative; in fact, in some ways, the role of nutrition in the onset of lithiasis has not yet been fully clarified.
What is certain is that any type of stone disease can only be traced back to an incorrect diet.
Why isn't diet always the most important factor?
More often than not, there is a genetic predisposition, a predisposing disease or disorder at the base of kidney stones.
Moreover, the calculations are not all the same. There are various types, for example:
- Calcium oxalate and calcium phosphate: 70-80% of cases
- Uric acid and calcium urate: 5-15% of cases
- Mixed: 5-10% of cases
- Infectious: 10-15% of cases
- Cystinics: 1-2% of cases.
Also for this reason, there cannot be a precise and universal diet to prevent the formation of kidney stones.
Importance of water
A single recommendation is unanimously agreed by doctors and researchers: to counteract the formation of kidney stones, it is essential to keep the body hydrated by taking the right amount of fluids in the diet.
By doing so, the substances present in the urine are diluted more, so the less chance they will precipitate and aggregate.
Of course, it is important not to overdo it: the water intake must always be proportionate to the content of the diet and physical activity, and never exaggerated (in addition to the risk of hydroelectrolytic imbalances, the consequent overwork of renal filtration could damage the functionality of the kidneys in predisposed individuals).
How much water to take
The treatment based on mineral waters (hydropinic treatment) cannot therefore be prolonged too long or carried out with excessive lightness without the prior medical consent.
Generally, we recommend a water consumption of about 2–3 liters per day (between drinks and food), so that the urinary volume is 2 liters over a 24 hour period.
At the same time, a generous intake of liquids is recommended, especially in critical periods, such as after large meals, during the night, in the presence of hydro-saline leaks in the gastrointestinal system (diarrhea, vomiting) and in case of excessive sweating during exercises. physical or living in an excessively hot-humid climate. Attention also to long journeys, especially by plane.
How to evaluate the state of hydration?
In general, very pale yellow urine (from semi-transparent to straw yellow) is a sign of proper hydration.
It is necessary to increase the water supply if the urine appears dark yellow or light brown.
What to drink in the diet for kidney stones?
Often, in the presence of kidney stones it is advisable to prefer water to other drinks, preferably choosing low-mineral or minimally mineralized waters, in order to limit the intake of sodium and calcium, whose increase in the urine can favor the formation of stones.
drinks to avoid
Coffee, tea and fruit juices (such as grapefruit, apple or cranberry juice) are foods rich in oxalates, so their consumption should be limited, especially in the presence of calcium oxalate stones. Green light, however, for lemon juice and lemonade, which, as we will see, can have a beneficial effect in many cases.
Calcium content: does it matter when choosing water?
We would like to point out right away that, more than quality, it is important to evaluate the quantity of water and liquids taken with the diet (broth, herbal teas, fruit juices, etc.).
Although some studies have shown that even mineral waters rich in calcium can be a protective factor, in the presence of stones it is generally recommended to use minimally mineralized waters which, as they are poor in mineral salts, favor diuresis and facilitate the expulsion of small kidney stones.
Differences in the Diet
Why is there no one-size-fits-all diet?
In addition to reduced fluid intake, certain eating habits can promote the appearance of kidney stones in predisposed individuals.
In this regard, it is first of all necessary to establish with certainty which type of stones afflicts the patient, since the dietary measures useful to prevent certain types of stones may be contraindicated in front of stones of different origin; as we said in the introduction, the calculations are not all the same.
At other times, such as in the presence of struvite stones that complicate recurrent urinary infections, the diet has little preventive effect; in the latter case, for example, antibiotic treatment becomes indispensable.
Goals of the diet against kidney stones
The kidney stone diet essentially has three goals:
- Increase the degree of dilution of these salts
- Increase the intake of substances, such as citric acid, which can inhibit its formation
- Reduce the factors that predispose the precipitation of salts responsible for the formation of the stone.
As explained above, dietary variations must always be prescribed and monitored by the attending physician, who knowing the "chemical identikit" of kidney stones can establish the most suitable diet.
pH of Urine
What does urine pH have to do with it?
Acidic urine is associated with stones of cystine, xanthine and uric acid, while in the presence of basic urine increases the risk of renal concretions of calcium phosphate, calcium carbonate, magnesium phosphate and struvite.
Calcium oxalate stones, the most common (60% of cases), develop more in neutral or alkaline urinary environments.
Influence of diet on urine pH
As for the influence of diet on urinary pH, acidic urine typically occurs in diets rich in meat, especially if preserved, and alkaline urine in vegetarian diets or more generally rich in vegetables and fruit (with the exception of plums and blueberries) .
Lemon juice and potassium citrate are two of the most widely used urinary alkalizers, and as such they are particularly suitable in the presence of cystine and uric acid stones. In these cases, the urine is alkalized to pH values close to neutral (6,5-7).
Exceeding values of 7,5 increases the risk of kidney stones of calcium phosphate, calcium carbonate, magnesium phosphate and struvite. In these cases, the alkalinization of the urine would therefore end up worsening the patient's clinical picture.
Meat and fish
Meat and fish in uric acid kidney stones
A diet rich in meat leads more frequently to uric-type kidney stones.
In fact, due to the excessive consumption of proteins, the urine becomes more acidic and increases the rate of elimination of calcium and uric acid, while that of citrates (substances that prevent the precipitation of these salts) is lowered.
If there is a predisposition to kidney stones of uric origin (accumulation of uric acid), all those foods rich in purines such as anchovies, herring, sardines, crustaceans, liver, sweetbreads, kidneys, heart, game, geese and pigeons, should be limited.
Instead, the intake of urinary alkalizers such as potassium citrate and magnesium citrate should be encouraged. In fact, the solubility of uric acid increases significantly with the alkalinization of the pH of the urine, to the point that sometimes medical therapy with urinary alkalizers alone is capable of dissolving stones exclusively composed of uric acid.
Conversely, in the presence of acidic urine, uric acid tends to precipitate.
Meat and fish in calcium phosphate kidney stones
On the other hand, and here we find yet another invitation to evaluate with the doctor and possibly with the dietician the most suitable diet in the presence of kidney stones, excessive alkalinization of the urine (pH> 7) facilitates the precipitation of calcium phosphates.
Meat and fish in kidney stones from cystine
Being rich in methionine (an amino acid precursor of cystine), the products rich in proteins should be limited even in the presence of kidney stones of cystine origin, which in the same way benefit - from a preventive and therapeutic perspective - urinary alkalinization.
Vegetables and Fruits
Is vegetables good or bad for kidney stones?
Fruits and vegetables increase the elimination of citrates, very effective substances in preventing the formation of stones.
For this reason, lemon juice - which contains about 5-7% citric acid - is the ideal food for those suffering from kidney stones (although, due to the risk of alkalizing the urine too much, it should be limited in the presence of calculations of calcium phosphate, calcium carbonate, magnesium phosphate, struvite or calcium oxalate).
However, we must not forget that foods of plant origin are also rich in oxalates.
Do oxalates predispose to kidney stones?
An excess of oxalic acid in the diet has been shown to be particularly harmful, as it promotes the synthesis of calcium oxalate kidney stones.
Food sources of calcium oxalate
Calcium oxalate is found almost everywhere, but some foods are particularly rich in it: chocolate, hazelnuts, cola and carbonated drinks in general, fruit juices, tea, cabbage, peas, asparagus, spinach and rhubarb.
Vegetable oxalates: worsening of certain kidney stones
Some vegetables, such as chard, beets, spinach and parsley, are particularly rich in oxalates, so ingesting large quantities of these foods could promote the appearance of calcium oxalate stones.
Under normal conditions, about 20% of urinary oxalate comes from the diet.
Its intestinal absorption increases during enteric inflammatory diseases, which include Crohn's disease, ulcerative colitis and other less frequent disorders.
Role of the low-oxalate diet
It must be emphasized that in case of physiological overproduction of oxalate, reducing the consumption of these foods that are rich in it prevents kidney stones, but it does so only in a marginal way.
What therefore matters, once again, is not so much the overall introduction of oxalates, but rather the degree of intestinal absorption, the endogenous synthesis and the relative quantity of liquids present in the diet.
In any case, in the presence of this type of stones, it is important to limit the consumption of these foods, or to introduce them together with a source of calcium (supplements or dairy products) in order to reduce intestinal absorption.
Reduce vegetables to decrease oxalates: side effects
Reduction of folic acid
Due to the intake of folic acid, which contributes to meet the nutritional needs of pregnant women and perhaps to prevent the cardiovascular risk associated with hyperhomocysteinemia, a reduction in the consumption of these foods may still not be advisable from a medical point of view.
Vitamin K reduction
The same goes for the intake of vitamin K in patients taking anticoagulant drugs such as coumadin.
Hence the importance and the absolute need to discuss in advance with your doctor any dietary modification in a preventive perspective, avoiding any extremization of the concepts set out in the article.
Nutrients that hinder the formation of calcium oxalate stones
fruit and vegetables
The intake of foods rich in citric acid or potassium citrate seems useful to reduce the formation of calcium oxalate stones in the urine: the citrate, in fact, is salified with calcium, reducing the free share of the mineral in the urine.
role of phytic acid
In the presence of urinary tract stones, a diet rich in waste is not recommended, as the phytic acid contained in foods of plant origin (vegetables, fruit and whole grains) binds with calcium forming insoluble and non-absorbable compounds.
Salt and Sodium
Negative effects of salt and sodium
Salt, sodium and calcium oxalate stones
A diet rich in salt, and more generally in sodium, increases the urinary excretion of calcium and reduces the pH of the urine and the excretion of citrate, thus favoring the formation of calcium oxalate kidney stones.
For this reason, and in order not to increase the risk of other unpleasant conditions (hypertension, osteoporosis), it is recommended to take no more than 6-8 grams of salt per day.
Foods to avoid
In particular, it is good to pay attention to salted foods, cured meats, cheeses, preserves, snacks and other packaged foods, as they are "hidden" but very important sources of sodium (see: is salt bad for you?).
Calcium and Vitamin D
The right amount of calcium is beneficial
The role of calcium in the formation of kidney stones has always been the subject of numerous studies and research.
Today it has been concluded that in the healthy population a diet rich in calcium not only does not predispose to urinary tract stones, but can even prevent it by reducing the absorption of oxalic acid.
A daily intake of 1200 mg of calcium is therefore recommended, of which 800 mg provided by dairy products.
excess of Vitamin D: a predisposing factor
An excess of vitamin D in the diet - very difficult to achieve with food alone - promotes intestinal absorption of calcium, causing hypercalcemia (excess calcium in the blood) and hypercalciuria (excess calcium in the urine).
This could occur in a patient who regularly takes calcium and vitamin D supplements to fight or prevent osteoporosis.
Beneficial effect of alcohol
Renal excretion of uric acid and oxalates is decreased by alcohol consumption.
This suggests that a moderate consumption of alcoholic beverages (1-3 units per day) can have a beneficial effect on the prevention of kidney stones.
Side effects of alcohol abuse
On the other hand, we must not forget that excess ethyl alcohol significantly predisposes to dehydration. As we have already seen, a dehydrated body is more prone to the formation of kidney stones.
Excess sugar in sweets increases the risk of kidney stones
An excessive consumption of sugars in the diet increases the elimination of calcium in the urine, consequently the risk of stone formation.
Furthermore, some typical ingredients of sweets (cocoa) are particularly rich in oxalate.
Potassium has a beneficial effect on calcium stones
According to some authors, foods rich in potassium (beans, apricots, peas, potatoes, garlic and dried fruit) reduce the urinary excretion of calcium without interfering with the intestinal absorption of the ion.
Excess of vitamin C and risk of kidney stones
An excess of vitamin C (or ascorbic acid) in the diet also seems to favor the synthesis of kidney stones, due to the increased endogenous production of oxalates.
For this reason, especially if you have a history of calculosis, it is generally recommended to limit the overall dietary intake of vitamin C (diet plus any supplements) to no more than 1 g per day.
The risk that vitamin C can metabolise into oxalates is higher in pyridoxine (vitamin B6) deficiency, as can happen in case of dicolytes with recurrent diarrhea.
Therefore, before taking vitamin C supplements, people with calcium oxalate stones should have additional medical examinations.
- LEMON AND CITRUS JUICES: the citric acid contained in these foods can be particularly useful to patients suffering from uric acid stones, because it increases the urinary pH and the excretion of citrate, factors that reduce the formation of crystals and uric acid that of cystine. As explained in the course of the article, the consumption of lemon juice for therapeutic purposes may be contraindicated in the presence of calcium stones, which develop more in neutral or alkaline urinary environments.
- ONION: has a powerful diuretic effect and promotes the elimination of uric acid.
- PARSLEY: stimulates appetite and digestion, promotes diuresis by eliminating small kidney stones (renella).
- CELERY: has diuretic properties, with an effective draining action on the liver and respiratory tract; it is therefore useful in case of kidney stones and liver failure.
- ARTICHOKE, CABBAGE, APPLE AND NETTLE: increase the excretion of urine.
Other articles on 'Diet and Kidney Stones'
- Drugs for the treatment of kidney stones
- kidney stones
- Kidney stone symptoms
- Kidney stones: care and treatment
- Kidney stone remedies