Generality
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 appearance of lithiasis has not yet been fully clarified.
Why isn't diet always the most important factor?
Most often, at the base of kidney stones there is a predisposition of genetic origin, a predisposing disease or disorder.
Moreover, the calculations are not all the same. There are various types, for example:
- Calcium oxalate and calcium phosphate: 70-80% of the cases
- Uric acid and calcium urate: 5-15% of cases
- Mixed: 5-10% of cases
- Infectious: 10-15% of cases
- Cystinic: 1-2% of cases.
Also for this reason, there cannot be a precise and universal diet to prevent the formation of kidney stones .
water
Importance of water
A single recommendation finds a unanimous consent from doctors and researchers: to counteract the formation of kidney stones it is essential to keep the body hydrated, taking the right amounts of liquids with the diet.
In doing so, the substances present in the urine are more diluted, so the fewer the chances are that they will fall and aggregate.
Of course, it is important not to exaggerate: the water supply must always be proportionate to the level of nutrition and physical activity, and never exaggerated (in addition to the risk of hydroelectricity imbalances, the consequent hyper-work of renal filtration could damage the functionality of the kidneys in predisposed individuals).
How much water must be taken
The treatment based on mineral waters (hydropinic treatment) cannot therefore be continued for too long or conducted with excessive lightness without the prior medical consent.
Generally, water consumption of around 2–3 liters per day (between drinks and food) is recommended, so that the urinary volume is 2 liters over 24 hours.
At the same time, a generous supply of liquids is recommended, especially in critical periods, such as after large meals, during the night, in the presence of gastrointestinal water-saline losses (diarrhea, vomiting) and in case of excessive sweating during exercises physical or stay in an excessively hot-humid climate. Attention also to long journeys, especially by plane.
How to assess 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 intake if the urine appears dark yellow or light brown.
What to drink in the diet for kidney stones?
recommended drinks
Often, in the presence of kidney stones it is advisable to prefer water to other beverages, preferably choosing mineral water or minimally mineralized water, in order to contain the intake of sodium and calcium, whose increase in 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. Go ahead, however, to lemon juice and lemonade, which as we shall see may in many cases have a beneficial effect.
Calcium content: is it important in the choice of water?
We specify right from the start that, more than quality, it is important to evaluate the quantity of water and liquids taken with the diet (broth, herbal tea, fruit juices etc.).
Although some studies have shown that even calcium-rich mineral waters can constitute a protective factor, in the presence of stones it is generally advised to use minimally mineralized waters which, as they are poor in mineral salts, favor diuresis and facilitate expulsion of small kidney stones.
Differences in the Diet
Why is there no equal diet for everyone?
In addition to reduced fluid intake, some eating habits may favor the appearance of kidney stones in predisposed individuals.
In this regard, it is first of all necessary to establish with certainty what typology of calculations afflicts the patient, since the dietary measures useful to prevent certain types of calculations can be contraindicated before calculi of different origin; as we said in the introduction, the calculations are not all the same.
Other times, as in the presence of struvite stones that complicate recurrent urinary infections, the diet has little preventive effect; in the latter case, for example, an antibiotic treatment becomes indispensable.
Diet goals against kidney stones
The diet for kidney stones aims essentially at three goals:
Reduce the urinary excretion of the salts responsible for calculus formation:
- Increase the degree of dilution of these salts
- Increase the intake of substances, such as citric acid, which can inhibit their formation
- Reduce the factors that predict the precipitation of salts responsible for calculus formation.
As explained above, dietary variations must always be prescribed and monitored by the attending physician, who by knowing "the chemical identikit" of kidney stones can establish the most suitable diet.
pH of the Urine
What does urine pH have to do with it?
Acid urine is associated with cystine, xanthine and uric acid stones, while in the presence of basic urine the risk of renal calcium phosphate, calcium carbonate, magnesium phosphate and struvite concretions increases.
Calcium oxalate stones, the most common (60% of cases), develop most in neutral or alkaline urinary environments.
Influence of diet on urine pH
As for the influence of the diet on urinary pH, acid urine is typically present in diets rich in meat, especially if preserved, and alkaline urine in vegetarian or more generally diets rich in vegetables and fruit (with the exception of prunes and blueberries) .
The juice of lemons and potassium citrate are two of the most used urinary alkalizing agents, and as such they are particularly indicated in the presence of cystine and uric acid stones. In these cases, the urine is alkalized to pH values close to neutrality (6.5-7).
Exceeded 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 a uric-type kidney stone.
In fact, due to the excessive consumption of proteins, urine becomes more acidic and increases the amount of elimination of calcium and uric acid, while that of citrates is lowered (substances that prevent the precipitation of these salts).
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.
The intake of urinary alkalinisers such as potassium citrate and magnesium citrate should be encouraged. In fact, the solubility of uric acid increases significantly with the alkalinization of the urine pH, to the point that sometimes medical therapy with urinary alkalinizers alone is capable of dissolving calculi 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 the umpteenth invitation to evaluate with the doctor and possibly with the dietician the most suitable diet in the presence of kidney stones, the excessive alkalinization of the urine (pH> 7) facilitates the precipitation of calcium phosphates.
Meat and fish in cystine kidney stones
Being rich in methionine (an amino acid precursor of cystine), protein-rich products should also be limited in the presence of kidney stones of cystinic origin, which likewise benefit - in preventive and therapeutic terms - from urinary alkalization.
Vegetables and Fruits
Is vegetables good or bad for kidney stones?
Fruits and vegetables increase the elimination of citrates, substances that are very effective 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 proved 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, coca cola and carbonated drinks in general, fruit juices, tea, cabbage, peas, asparagus, spinach and rhubarb.
Vegetal oxalates: worsening of certain kidney stones
Some vegetables, such as beets, beets, spinach and parsley, are particularly rich in oxalates, so the ingestion of large quantities of these foods could favor 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 should be noted that in the case of overproduction of oxalate physiology, reducing the consumption of these foods that are rich in them prevents kidney stones, but does so only marginally.
What therefore counts, 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.
However, in the presence of this type of stones it is important to limit the consumption of these foods, or introduce them together with a source of calcium (supplements or dairy products) in order to reduce intestinal absorption.
Reduce vegetables to reduce oxalates: side effects
Folic acid reduction
Due to the intake of folic acid, which helps to satisfy the nutritional needs of pregnant women and perhaps prevent the cardiovascular risk associated with hyperhomocysteinemia, a reduction in the consumption of these foods may not be advisable from a medical point of view.
Reduction of vitamin K
The same applies to the intake of vitamin K in patients taking anticoagulant drugs such as coumadin.
Hence the importance and the absolute necessity to discuss in advance with your doctor any dietary modification from a preventive point of view, avoiding any extremes of the concepts presented in the article.
Nutrients that hinder the formation of calcium oxalate stones
fruits 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: citrate, in fact, is salified with calcium, reducing the free portion of the mineral in the urine.
role of phytic acid
In the presence of urinary calculosis, a diet rich in slag is recommended, as the phytic acid contained in foods of vegetable 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 sodium, increases the urinary excretion of calcium and reduces the pH of the urine and the excretion of citrate, thus favoring the formation of renal calcium oxalate 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, meats, cheeses, preserves, snacks and other packaged foods, as "hidden" but very important sources of sodium (see: does salt hurt?).
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 calculosis of the urinary tract, 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 are supplied by dairy products.
excess Vitamin D: a predisposing factor
An excess of vitamin D in the diet - very difficult to achieve with diet alone - promotes intestinal calcium absorption, causing hypercalcemia (excess calcium in the blood) and hypercalciuria (excess calcium in the urine).
This may occur in a patient who regularly takes calcium and vitamin D supplements to fight or prevent osteoporosis.
Alcohol
Beneficial effect of alcohol
Renal excretion of uric acid and oxalates is diminished by alcohol consumption.
This suggests that a moderate consumption of alcoholic beverages (1-3 units a 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 predisposes significantly to dehydration. As we have already seen, a dehydrated organism is more prone to the formation of kidney stones.
Desserts
Excess sugar contained in sweets increases the risk of kidney stones
An excessive consumption of sugars with the diet increases the elimination of calcium in the urine, consequently the risk of calculations forming.
In addition, some typical sweet ingredients (cocoa) are particularly rich in oxalate.
Potassium
Potassium has a beneficial effect on calcium stones
According to some authors, foods rich in potassium (beans, apricots, peas, potatoes, garlic and nuts) would reduce the urinary excretion of calcium without interfering with the intestinal absorption of the ion.
C vitamin
Excess vitamin C and risk of kidney stones
Even an excess of vitamin C (or ascorbic acid) in the diet 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 in your back, 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.
pyridoxine deficiency
The risk that vitamin C can metabolize in oxalates is higher in pyridoxine deficiency (vitamin B6), as can happen in case of colitis with recurrent diarrhea.
Therefore, before taking supplements based on vitamin C, carriers of calcium oxalate stones should carry out further medical tests.
Recommended Foods
- LEMON AND CITRUS JUICE: 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 article, the consumption of lemon juice for therapeutic purposes can be contraindicated in the presence of calcic calculosis, which develops 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: it has diuretic properties, with an effective draining action on the liver and on the respiratory tract; it is therefore useful in cases of kidney stones and liver failure.
- ARTICHOKE, CABBAGE, APPLE AND NETTLE: increase urine excretion.
