Q&A: What people with diabetes should know about preventing kidney stones
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Susan Weiner, MS, RDN, CDN, CDCES, FADCES, talks with Melanie Betz, MS, RD, CSR, FNKF, FAND, about preventing kidney stones through diet and nutrition.
Weiner: What are kidney stones? What makes a kidney stone?
Betz: Kidney stones are a crystallization of minerals that form in urine anywhere along the urinary tract or kidneys. Kidney stones form when the supersaturation of lithogenic materials gets too high. Many different aspects of urine affect kidney stone supersaturation, such as the amount of calcium, oxalate and citrate, as well as urine pH. Of course, the most important factor in supersaturation is urine volume. The more urine you make, the less saturated it will be with lithogenic materials.
Nearly 80% of kidney stones are made from calcium and oxalate. Calcium phosphate and uric acid kidney stones are also common. Cystine kidney stones are associated with the rare genetic condition cystinuria. Struvite kidney stones are almost exclusively related to infections.
Men are at higher risk for kidney stones, although the prevalence is increasing among women much faster than among men. White people are at higher risk as are those following the typical American diet that is high in sodium, animal protein and added sugar, along with inadequate fruit, vegetables and calcium. Certain medical conditions also increase risk for stones, such as idiopathic hypercalciuria, primary hyperparathyroidism, inflammatory bowel disease, short gut syndrome, gout, eating disorders and a history of malabsorptive bariatric surgery.
Weiner: Are kidney stones more prevalent among people with diabetes?
Betz: People with diabetes are 60% more likely to have kidney stones compared to the general population. The increased risk is to lower urine pH. Insulin resistance makes it harder for kidneys to produce ammonium, which results in more acidic urine. A urine pH less than about 5.8 makes uric acid kidney stones much more likely to form.
People with diabetes also tend to have more calcium and less citrate in their urine, making calcium-based stones more likely as well.
Weiner: Can kidney stones be prevented?
Betz: Yes, kidney stones can absolutely be prevented. The statistic that 50% of people who form one kidney stone will have another in their lifetime is frequently quoted. However, this is in a medical system where only about 10% of patients get a single 24-hour urine test. A 24-hour urine test kidney stone is critical to understand why someone is forming kidney stones and, therefore, what a personalized, effective kidney stone prevention plan might be for that particular person. I often wonder how much lower that 50% statistic might be if personalized kidney stone prevention were routinely part of kidney stone care.
Weiner: Does nutrition play a role in kidney stone prevention or treatment?
Betz: Nutrition plays a critical role in the prevention of kidney stones. What you eat plays a huge role in preventing the formation of new stones or inhibiting the growth of existing stones.
There is no single “kidney stone diet.” Nutrition for kidney stone prevention must be personalized to each person’s 24-hour urine test results. These results will reveal urine risk factors for forming more stones. From there, dietitians can determine what dietary changes will be effective for stone prevention.
Urine risk factors can be very different even for the same type of kidney stone. For example, one person could be forming calcium oxalate stones due to high urine calcium and another due to low urine citrate. The ideal nutrition for each person would be very different.
Here the most common nutrition recommendations I make for people, based on their 24-hour urine test results:
- Drink more. The American Urological Association guideline recommends drinking enough fluid to produce at least 2.5 of urine output per day. For most people, this means aiming for about 3 of fluid each day.
- Limit sodium to 2,300 mg per day. The more salt we eat, the more calcium ends up in our urine.
- Limit nondairy animal protein. Excess protein from beef, pork, chicken, fish and other seafood can increase urine calcium and oxalate and lower urine pH and citrate. Eating a more moderate amount of protein or swapping some of that animal protein for dairy or plant protein can be very helpful.
- Get in enough calcium. Ironically, it is critical for people with calcium oxalate stones to eat enough calcium. Dietary calcium significantly inhibit the amount of oxalate absorbed from food thereby reducing urine oxalate and risk for oxalate stones. Getting in enough calcium (1,000-1,200 mg per day) is the most effective way to reduce urine oxalate levels. Calcium is also important for people with calcium-based stones given their higher risk for osteopenia and fractures.
- Watch the added sugar. Eating a lot of added sugar is associated with kidney stones, likely due to higher levels of urine calcium.
- Do not limit dietary oxalate. Historically, low oxalate diets were recommended for kidney stone prevention. However, we now understand that low oxalate diets limit many healthy foods like most vegetables, many fruits and all whole grains, nuts, seeds and beans. Ironically, these exact foods are packed with things good for calcium kidney stone prevention, like magnesium, potassium, alkali phytate. Reducing dietary oxalate will lower urine oxalate but will also limit these powerful kidney stone inhibitors. Dietary patterns very high in oxalate, such as the Mediterranean diet or the Dietary Approaches to Stop Hypertension (DASH) diet, are consistently associated with a much lower risk for kidney stones, despite their very high oxalate content. No research has been published connecting low oxalate diets with a reduction in kidney stone formation.
Weiner: Can you have kidney stones with no symptoms? Why are they so painful?
Betz: Asymptomatic kidney stones are common. Kidney stones can be present in kidneys for a long time and cause no issues. The problem comes when they become dislodged and start moving down the urinary tract.
Weiner: Do any beverages or supplements promote kidney stones?
Betz: In susceptible populations, electrolyte drinks, such as Liquid IV, and collagen or other protein supplements could cause kidney stones. One packet of Liquid IV has 510 mg sodium along with 11 g of added sugar. Since most people are already consuming much more sodium and added sugar than they need, this additional sugar and sodium could further increase their risk for stones by driving up urine calcium.
Collagen supplements are essentially a specialized protein supplement. Since most people are eating more protein than they need, protein supplements are just adding even more unnecessary protein. As excess nondairy animal protein can drive up urine calcium and oxalate, and drive down urine citrate and pH, there is potential for any protein supplement to promote stone formation in susceptible people.
Collagen, specifically, is made up primarily of the amino acids proline, glycine and hydroxyproline. The liver can make oxalate from hydroxyproline and glycine. There is no research specifically on collagen supplements and kidney stones, but given the potential for a much higher endogenous production of oxalate from hydroxyproline and glycine, I do have concerns about collagen for people with oxalate kidney stones.
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For more information:
Melanie Betz, MS, RD, CSR, FAND, is a nationally recognized researcher and educator in kidney stone nutrition. She is founder and CEO of The Kidney Dietitian. She is the Renal Practice Group of the Academy of Nutrition and Dietetics and the National Kidney Foundation of Illinois. She can be reached at hello@thekidneydietitian.org; X (Twitter): @thekidneyrd.
Susan Weiner, MS, RDN, CDN, CDCES, FADCES, is co-author of The Complete Diabetes Organizer and Diabetes: 365 Tips for Living Well. She is the owner of Susan Weiner Nutrition PLLC and is the Endocrine Today Diabetes in Real Life column editor. She can be reached at susan@susanweinernutrition.com; X (Twitter): @susangweiner
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