Is Medical Nutrition Therapy Appropriate for Kidney Stones?

The medical management of kidney stones involves a metabolic evaluation, including a 24-hour urine collection. Serum assessment of additional markers, including electrolytes, parathyroid hormone, vitamin D, and/or uric acid levels, may also be done. Once the source of the stone is determined, dietary modifications may be warranted, but regardless of what the stone is comprised of, there is not always a direct nutritional cause for high levels of calcium (hypercalciuria), oxalate (hyperoxaluria), uric acid (hyperuricosuria), or low amounts of citrate (hypocitraturia) in the urine.

As with any other treatment plan, the nutrition therapy provided by the registered dietitian nutritionist should be individualized based on the patient's current health status and known risk factors. Reviewing the patient's diet history will help to determine if there is an excess or deficiency in any of the nutritional components that might influence the urinary profile.

For example, excessive intake of sodium and foods with a high potential renal acid load (PRAL), such as meat, poultry and other animal products, may contribute to hypercalciuria and hypocitraturia. Hyperoxaluria may be a consequence of diets that are high in oxalates and low in calcium, magnesium and dietary fiber. In the case of hypercalciuria and hyperuricosuria, an excessive intake of refined carbohydrates may play a role. Struvite stones are often a result of kidney infections in females and while nutritional interventions are lacking for their treatment, cranberry juice has been found to aid in decreasing urinary pH.

In the past, a low calcium and low oxalate diet was advised for the treatment of calcium oxalate stones. While that approach may still be required in some cases, more recent research has suggested that most individuals who are susceptible to these stones should aim for the daily recommended amount of calcium and limit sodium and foods with a high PRAL instead.

Balancing the renal acid load can be achieved by including more fruits, vegetables, since they supply magnesium and potassium, two micronutrients that have been associated with a lower incidence of kidney stones. Decreasing sources of purine from animal proteins also can help in the treatment of uric acid stones. Given these factors, it's perhaps unsurprising that some research has indicated a DASH-style eating pattern significantly lowered the risk for kidney stones. Individuals who follow a vegetarian eating pattern have also been found to develop kidney stones at a third of the rate of those who consume animal proteins.

Regardless of the stone type, there is usually a need to increase fluid intake in order to achieve a urinary output goal of 2 or more quarts per day. There is lack of agreement regarding which fluids to encourage, and barriers to increasing fluid intake exist and need to be taken into consideration when counseling clients who have developed kidney stones. Some beverages act as mild diuretics, such as coffee and tea, and may help increase urinary output; whereas, other sources that include citrate (i.e., citrus fruits) have been shown to increase urinary pH and help prevent some types of stone formation.

In coordination with the rest of the interdisciplinary team, the assessment of the patient's lab values and potential nutritional risk factors will allow RDNs to provide customized MNT for the treatment of kidney stones and help to minimize their recurrence.

References:

• Academy of Nutrition and Dietetics Nutrition Care Manual® Kidney Stones. Accessed June 8, 2022.
• Saxena A, Sharma RK. Nutritional aspect of nephrolithiasis. Indian J Urol. 2010 Oct-Dec; 26(4): 523–530. Accessed June 11, 2014.
• Lin BB, Lin ME, Huang RH, Hong YK, Lin BL, He XJ. Dietary and lifestyle factors for primary prevention of nephrolithiasis: a systematic review and meta-analysis. BMC Nephrol. 2020;21(1):267.
• Escott-Stump, S. Kidney Stones (Nephrolithiasis). In: Nutrition & Diagnosis Related Care, Ninth Edition. Chicago, IL: Academy of Nutrition and Dietetics; 2022:1167-1171.