What to avoid when having calcium oxalate kidney stones?

Calcium oxalate is a compound that crystallizes when oxalate binds to calcium. When calcium and oxalate levels in the urine are high for a long time, the crystals can form solid masses called kidney stones. According to the National Kidney Foundation, calcium oxalate stones are the most common type of kidney stone. About 75% of kidney stones are made up of either calcium oxalate or calcium oxalate.

Oxalate, also known as oxalic acid, is either derived from foods or produced when the liver breaks down (metabolizes) vitamin C and amino acids. Oxalate is considered a waste product. Under normal circumstances, oxalate binds with calcium in the intestines and is excreted in the stool. Excess, unbound oxalate is absorbed into the blood and excreted by the kidneys in the urine.

Calcium also leaves the body through urine and stool. Of the calcium that passes through the kidneys, most is reabsorbed into the blood for reuse in the body, with only a very small amount excreted in the urine. Calcium oxalate stones can form if these systems are disrupted by too much oxalate and calcium in the urine, too little calcium in the intestines for the oxalate to bind to, or too little urine volume.

A diet high in oxalate-containing foods is one of the causes of calcium oxalate stone formation by increasing calcium and oxalate levels. Diets high in protein, sodium, and high-fructose corn syrup also increase urinary oxalate excretion.

Some of these foods are rich in oxalate and should be limited to avoid recurrence of kidney stones, including avocado, beets, carrot juice, chocolate, cocoa, cornstarch, okra, peanuts, potatoes, raspberries, soybeans, sweet potatoes, and tea. Foods that should be completely avoided, especially for people with a history of recurrent kidney stones, include rainbow chard, spinach, and star fruit.

Some foods containing oxalates can be eaten by cooking them rather than eating them raw. Boiling is the most effective way to reduce the oxalate content of vegetables by up to 50%. Steaming is much less effective, and grilling has little effect on reducing oxalate levels. Limit foods high in salt, as high sodium intake can increase the amount of calcium in the urine, which can promote stone formation.

Keep protein intake to less than 30% of total daily calories. Protein is essential for a healthy diet, but overdoing it can lead to kidney stones. Include age-appropriate amounts of calcium in your diet. Too little calcium can increase oxalate levels. Choose calcium-rich foods such as milk, yogurt, cheese, dark green vegetables, and nuts instead of supplements. Take a daily vitamin D supplement to help your body absorb more calcium. Foods rich in vitamin D include fatty fish, mushrooms, and cheese.

Some experts also recommend the DASH diet, which is a diet for people with high blood pressure that focuses on vegetables, fruits, whole grains, low-fat dairy, beans, fish, and poultry. According to a 2014 study in American Journal of Kidney Diseases, The DASH diet reduces calcium and oxalate levels in the kidneys, reducing the risk of calcium oxalate crystal formation. This diet is also effective for weight loss, reducing sodium and protein intake, so it is beneficial for people with calcium oxalate stones.

In general, calcium oxalate stones smaller than 4 mm are able to pass from the body on their own. Larger stones may require medical intervention such as surgery or endoscopic lithotripsy. Compared to other types of kidney stones, calcium oxalate stones are the most likely to recur. To limit this condition, in addition to the above diet, patients should drink enough water, about two liters per day to increase urine volume and dilute urine to prevent new stones from forming.

Obese people should lose weight. A body mass index (BMI) over 30 increases oxalate production in the liver and increases compounds such as uric acid, which promote calcium oxalate crystallization. Medications such as diuretics and calcium citrate supplements can also prevent stones from recurring if lifestyle changes are not effective.