Kidney Stone Diet: How to Prevent Nephrolithiasis

Common signs and symptoms of kidney stone disease include:

• Severe pain in the side, back, lower abdomen, or groin
• A burning or painful sensation while urinating
• Frequent urination, often only able to pass small amounts
• Bad-smelling, cloudy, pink, red, or brown coloured urine
• Nausea and vomiting, or fever and chills if the condition worsens

Some kidney stones are as small as a grain of sand and pass through the urinary tract with little or no pain. However, larger kidney stones may become stuck in the urinary tract and block the flow of urine, causing severe pain. Pain relievers may ease discomfort caused by small stones, while surgery may be required in more severe cases.

A core part of any kidney stone diet is limiting sodium. High sodium intake increases calcium excretion in the urine, raising the risk of calcium stone formation. We are advised to avoid high sodium intake by limiting salt to no more than one teaspoon per day, replacing it with herbs and spices such as garlic, ginger, cumin, and turmeric powder.

It also helps to limit sauces such as ketchup and salad dressing, which are often high in sodium. Other high-sodium foods to watch for include canned food, highly processed foods such as sausage and luncheon meat, and fast food.

Oxalate is naturally found in many everyday foods, so moderation - not full elimination - is the goal of a sensible kidney stone diet:

• Limit spinach, beet, rhubarb, chard, and root vegetables such as sweet potatoes and potatoes to under 100g (without skin, which has lower oxalate content)
• Limit fruits such as starfruit, berries, and dried figs
• Limit nuts like peanuts, almonds, cashews, walnuts, and pecans
• Limit chocolate, soy, and wheat bran

There is often a misconception that reducing calcium intake will reduce the risk of calcium stones. In reality, adequate calcium intake (around 800-1200 mg/day) helps reduce calcium stone formation, because calcium binds oxalate in the stomach or intestine, reducing oxalate absorption into the body and the risk of calcium oxalate forming in the kidney.

Dietary sources of calcium fall into two categories: dairy (milk, cheese, yoghurt) and non-dairy (chia seed, broccoli, chickpeas, and kale). When following a kidney stone diet, it is best to select calcium-containing foods that are lower in salt and added sugar.

Limiting animal protein may reduce the risk of kidney stones. Examples of animal-based protein include chicken, pork, beef - especially organ meat - eggs, fish (anchovies, sardines, mackerel, herring), and shellfish (scallops, shrimp, and mussels).

Animal proteins rich in purine content, such as anchovies, sardines, mackerel, herring, and organ meats, may increase uric acid production, which can make urine more acidic. It is therefore better to consider replacing some animal protein with plant-based protein, such as dried peas, beans, and lentils, which are less likely to produce acidic urine.

Drinking plenty of water is one of the simplest and most effective ways to help prevent kidney stone formation. Inadequate fluid intake results in concentrated urine (dark yellow in colour), which allows minerals to crystallise and stick together more easily.

It is recommended to drink at least 2.5 litres of water every day, with plain water preferred over other beverages. You can add lemon juice to plain water to enhance the taste. It is best to avoid sugar-sweetened beverages, although 100% pure fruit juice in moderation is acceptable.

High doses of vitamin C consumption can increase the risk of oxalate production in the body, since excess vitamin C is metabolised into oxalate. It is best to get your daily dose of vitamin C from fruits and vegetables rather than from high-dose supplements, in line with the Dietary Reference Intake.

The right kidney stone diet depends on the type of stone you are prone to forming: