Managing kidney stones with nutrition 

Incidence of kidney stones continues to grow in the United States. More common in men than women, risk for stone formation can be influenced by genetics, climate, diet and other comorbidities. While some individuals remain asymptomatic, others may experience significant pain with passage of a kidney stone. Identifying ways to prevent future stone development is necessary and for many, this includes a change to what they eat. Registered dietitian nutritionists (RDNs) can play an integral role with treatment by recommending beneficial diet modifications. 

Importance of the urine analysis

Before the RDN can determine what will be most helpful in terms of diet, collection and interpretation of a urine analysis is recommended. Completed over a 24-hour period, this measurement includes total urine volume and pH level along with calcium, phosphorus, oxalate, citrate, sodium and uric acid. Assessment of the urine analysis helps in determining next steps for stone prevention. Alterations seen that increase the risk for stone development include: 

• High urine calcium, uric acid or oxalate
• Low urine volume, magnesium and citrate

Depending on these measurements, each can contribute to urine concentration and saturation.  Most experts suggest at least two, 24-hour urine collections to compare for consistency but others suggest one sample is reasonable. One tip for patients before the analysis begins is to maintain normal diet and fluid intake before and during the test to best capture contributors to the development of their kidney stones.  

Stone types and significance

There are several different types of kidney stones with calcium oxalate, calcium phosphorus and uric acid being more routinely diagnosed over cystine and struvite stones.  Diet seems to play the most influential role with calcium or uric acid-based stones.  Cystine stones tend to develop more in those with a family history of this type, and struvite stones often develop following a urinary tract infection.  In addition to diet modifications, treatment or prevention may include supplementation, medications, and in some cases, surgical intervention.   

General diet recommendations

It’s important to remember that while general diet suggestions for kidney stone prevention can be used by the RDN with patients, there is no single diet that will apply to all patients because of the difference in stone types. Rather, determining which type is the problem is necessary in optimizing individual nutrition goals for each patient.  

Sodium

Comparable to other disease states, limiting total sodium intake to 2,300 mg or less per day is recommended to lower the risk of kidney stones. Too much can result in higher urinary calcium, changes with urine saturation and potential for stone development. Guiding the patient to read labels for higher sodium foods, understanding the benefits of selecting foods naturally low in sodium and limiting added salt with cooking are each important for reaching this goal. You may be asked about the benefits of using different salt types (for example, sea salt over sodium chloride), but the truth is they are both sodium-containing and can add up quickly if not monitored. 

Fluid

One of the more important points of patient education when working with individuals at risk for kidney stones is the need for fluids.  Standard fluid recommendations for the general population are too low.  Instead, the RDN should highlight an amount of 3 liters or more per day (depending on the individual) to help increase total volume and dilute saturation of urine.  Climate, especially for those in a warmer environment, may further increase fluid goals.  While water is important to push as the main beverage, benefits have also been seen with the addition of coffee, tea, lemonade, and milk.  Depending on the type of stone, soda or sugar-containing fluids may or may not be recommended.  

Protein

The type and amount of protein consumed can impact calcium excretion from the kidneys and contribute to changes with the renal acid load. Increased intake of animal-based protein, especially those high in purine, can lead to these changes while plant-based sources do not have this same effect. A moderate amount of non-dairy animal protein should be encouraged as part of a balanced diet with individuals more at risk for calcium-based or uric acid stones.   

Calcium

While encouraged for good bone health, total calcium from food and supplements needs to be monitored for kidney stone prevention. In general, research suggests a goal of 1,000 to 2,000 mg per day especially for those who struggle with calcium-oxalate stones. For other kidney stone types, calcium goals should be individualized. One added benefit of consuming some sources with calcium is their effect on high oxalate foods.  Eaten together, calcium binds to the oxalate, reduces overall absorption and increases urine excretion of this nutrient.   

Oxalate

Oxalate can be found in many different food choices including berries, chocolate, leafy greens, rhubarb, almonds, cashews and wheat bran among others.  An overly restrictive diet is not recommended because of the health benefits of these foods, but reducing high oxalate sources is encouraged. Daily goals for those at risk for stone formation average approximately 40 to 50 mg per day. This is most important for individuals with calcium-oxalate stones. With any oxalate-containing food, pairing with a calcium source can help limit nutrient absorption. 

Vitamin C

For those with an increased risk of kidney stone formation, goals for vitamin C complement the US Dietary Reference Intake. Suggested ranges of intake for adult women and men range from 75 to 90 mg per day. Vitamin C can be found naturally in citrus foods, added to foods sources or as an over-the-counter supplement. Of greatest concern is high-dose vitamin C supplementation (think 1,000 mg or more!). In such a high dose some of this supplement is metabolized into oxalate, which can increase certain stone formation. 

Vitamin D

An individualized approach is also recommended with vitamin D supplementation. Risk with stone formation centers around vitamin D’s influence on increasing calcium and phosphorus absorption. In general, experts recommend supplementation based on patient needs and vitamin D level status.    

Nutrition application

Diet education with kidney stone treatment remains an underutilized tool. While many patients have gotten a handout from their physician on foods to eat or foods to avoid, completing 1 on 1 counseling with an RDN for this condition is uncommon.  Creating awareness of this need and the benefits of nutrition education with an RDN can only help in optimizing patient care. 

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References: 

Gonyea J, Phillips S.  Clinical Guide to Nutrition Care in Chronic Kidney Disease. 3rd edition. Chicago, IL: Academy of Nutrition and Dietetics;2023. 

National Kidney Foundation. Kidney Stones. Available at https://www.kidney.org/atoz/content/kidneystones. Accessed March 27, 2024. 

National Institutes of Health Office of Dietary Supplements. Vitamin C: Fact Sheet for Health Professionals. Available at https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/. Accessed March 27, 2024. 

Academy of Nutrition and Dietetics. Nutrition Care Manual. Kidney Stones Nutrition Therapy. Available at https://www.nutritioncaremanual.org/. Accessed March 22, 2024. 

National Kidney Foundation. Kidney Stone Diet Plan and Prevention. Available at https://www.kidney.org/atoz/content/diet. Accessed March 22. 2024.