In the news: Diet and Recurring Kidney Stones   

Quick Primer on Kidney Stones

Kidney stones can be small or large irregularly shaped solid masses made up of millions of tiny crystals that form in the kidney. Kidney stones form when urine contains more crystal-forming substances (e.g. calcium, oxalate, and uric acid) than the fluid in urine can dilute. Additionally, urine may be short on substances that prevent crystals from sticking together – citrate and possibly magnesium for example.

Although stones originate in the kidney, when they start to move into one of the tubes connecting the kidneys to the bladder (the ureter) they can become wedged in the tube or the opening that leads to the ureter. This causes a backup of urine and can result in considerable pain.

Of the various types of kidney stones, about 80% are calcium based (calcium oxalate, phosphate), with calcium oxalate being most common by far. Other types include uric acid, struvite (associated with urinary tract infections), and cystine. Since stone formation is specific to individuals, determining the type of stone is key to establishing a personalized treatment plan to help prevent future stones.

Kidney stones are common, with more than 1 in 10 people affected. And kidney stones can come back: the recurrence rate is about 30% at 10 years. Having a family member who had kidney stones can up the risk for developing them.

There are factors in addition to heredity that can influence kidney stone risk, and diet is one of them. Excessive sodium, animal protein and oxalate (oxalic acid bound to minerals present in some fruits and vegetables) for example, have been associated with raising the risk for stones. And one of the biggest risk factor is not getting enough fluids every day.

New Study: Better Calcium & Potassium Intake May Help Prevent Stone Recurrence

Dietary recommendations for preventing kidney stones have been based primarily on factors linked to first time stone formation rather than on recurring stone. That led Mayo Clinic researchers to design a study to look at the impact of dietary factors in recurring stone formers(1,2). The results suggest that enriching diets with foods high in calcium and potassium may help prevent recurrent, symptomatic kidney stones.

The study had two groups of participants: over 400 people who had experienced first-time symptomatic kidney stones and a control group of about 380 who had not experienced kidney stones.

Of those first-time formers, 73 went on to have recurring stones during a median 4-year follow-up. The researchers found that low dietary calcium and potassium were linked to a lower risk for recurrence. In this study, the two minerals were even better predictors of recurrence than low fluid intake.

Risk factors associated with first-time formation were low dietary calcium and potassium, low fluid intake (less than about nine 12-ounce glasses), and lower levels of caffeine and phytate (an antioxidant found in whole grains and nuts).

Not enough fluid and low caffeine intake can result in low urine volume and more concentrated urine which contributes to stone formation. Phytate is considered an inhibitor of calcium oxalate crystal formation.

The authors recommend eating more dairy for calcium and fruit and vegetables for potassium.

Fruits and veggies do contain oxalates but they’re also high in citrate which helps prevent stone formation. There are usually reasons other than dietary oxalate for forming calcium oxalate stones. But for those advised to reduce oxalate, many fruits and veggies are high potassium / low oxalate including cherries, peaches, bananas, tomatoes, cantaloupe, peas, squash and butterleaf lettuce.

References

1. Chewcharat A, et al. Dietary risk factors for incident and recurrent symptomatic kidney stones. Mayo Clin Proc. 97:1437-48, 2022.
2. Diets higher in calcium and potassium may help prevent recurrent symptomatic kidney stones, Mayo Clinic finds. Mayo Clinic News Release. July 29, 2002.