Kidney Stone Diet: Fluids, Salt, Oxalate and Urine pH

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Which stone type do you have?

You can only adjust your diet in a useful way if you know the stone type. It is listed in the stone analysis report. Without an analysis, your urine pH can serve as a clue.

Stone type	Share	Forms with	Diet aims at
Calcium oxalate	about 75%	any pH, especially with little urine, high oxalate, low citrate	drinking, moderate oxalate, normal calcium, high citrate
Uric acid	10 to 15%	acidic urine below pH 5.5	raising urine pH to 6.2 to 6.8, lowering purines
Calcium phosphate	5 to 10%	alkaline urine above pH 6.5	keeping urine pH from going above 6.5, lowering salt
Struvite	5%	urinary tract infections	treating the infection; diet is secondary

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The five rules for every stone type

1. Drink, spread over the day. The goal is 2 to 2.5 liters of urine. That takes 2.5 to 3 liters of fluid, more in summer and when you exercise. Choose water, diluted juices, herbal tea and fruit tea. Have a glass before bed, because urine is most concentrated at night.

2. Salt under 6 g a day. Sodium pulls calcium into the urine with it: every extra gram of salt raises calcium excretion by about 20 mg. The biggest sources of salt are bread, cold cuts, cheese, ready meals and snacks, not the salt shaker.

3. Moderate protein, especially animal protein. 0.8 to 1 g per kg of body weight is enough. A lot of meat, fish and cheese raises the acid load, lowers citrate in the urine and increases the excretion of calcium and uric acid. Plant protein from legumes puts less strain on the system.

4. Don’t cut calcium. This is the most common mistake. Calcium from food binds oxalate in the gut, so less of it reaches the urine. People who avoid dairy form more stones, not fewer. Aim for 1,000 to 1,200 mg from milk, yogurt, cheese in moderation, kale, broccoli and calcium-rich mineral water, spread across your meals.

5. Plenty of vegetables and fruit. They provide potassium, magnesium and organic acids that end up in the urine as citrate. Citrate is the body’s most important stone inhibitor: it binds calcium and keeps crystals from growing. Citrus fruits, especially lemon, are the richest source of citrate.

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Urine pH: two directions, depending on the stone type

The PRAL of your diet directly determines your urine pH. An acid-heavy diet (meat, cheese, grains) lowers it. An alkaline-focused diet (vegetables, fruit, potatoes) raises it.

Uric acid stones form in acidic urine and can even partly dissolve at a pH above 6.2. Here, an alkaline-focused diet is part of the therapy: plenty of vegetables, fruit and potatoes, little meat, fish and cheese, no beer. The target pH is 6.2 to 6.8, often supported by prescription potassium citrate.

Calcium oxalate stones also benefit from an alkaline-focused diet, because it raises citrate and lowers calcium excretion. In a study with more than 180,000 participants, people with the most acid-heavy diet had a clearly higher stone risk than those with the most alkaline diet.

Calcium phosphate stones are the exception: they crystallize in alkaline urine. Here, your urine pH should stay below 6.5. Extreme alkaline cures or baking soda are counterproductive. Vegetables and fruit still make sense, because citrate protects here too. Fine-tuning belongs with your doctor.

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Oxalate: moderate, not zero

Foods high in oxalate include spinach, Swiss chard, rhubarb, beetroot, sorrel, almonds, cashews, peanuts, cocoa, sesame, wheat bran and black tea in large amounts. If you have calcium oxalate stones, eat these foods less often and in smaller portions, but don’t cut them out: spinach is still a valuable vegetable, once or twice a month instead of every week. The key is to eat high-oxalate foods together with calcium (spinach with a yogurt sauce, almonds with milk). Then the oxalate is bound in the gut.

Blanching lowers the oxalate content of leafy greens by 30 to 60 percent, because oxalate passes into the cooking water. Pour the cooking water away afterward.