Dietary changes can reduce the recurrence of—or even prevent—bothersome kidney stones
Diet has long been studied for its connection to kidney stone formation. Stone production occurs when there is an imbalance of metabolites (which enter our bodies through the foods we have consumed) that are excreted in our urine. The research in this area has grown tremendously in recent years, with studies showing a positive effect of different diet modifications in the prevention of kidney stone formation. While there currently is no cure for kidney stones, the following dietary recommendations may aid in preventing or at least reducing the recurrence of this bothersome problem in your known stone-forming patients.
Hydration Will Help
The significance of adequate fluid consumption in the prevention of kidney stones has been proven numerous times to decrease stone recurrence. The reduction can be as high as 50%.1 The increased fluid consumption assists in keeping the kidneys flushed and the urine dilute, therefore decreasing the rate of stone formation. The preventative effects of increased fluid consumption have been seen for all stone types. It is recommended that patients drink at least 2 L of fluid per day to help with kidney stone prevention.1,2 The type of fluid consumed should be taken into consideration, as not all beverages produce the same preventative results. Beverages with low sugar contents have the highest amounts of free water and therefore are the most efficient in diluting urine. Water, coffee, tea, orange juice, and lemonade have low sugar contents and have all been shown to decrease stone production.1,3 Sugary drinks such as sodas and sweetened fruit juices have actually been shown to increase the risk of stone formation, and should therefore be cautioned against.3
New Theories on Calcium
Calcium plays a major role in kidney stone production, as the majority of stones are formed from calcium-oxalate. Research and recommendations concerning calcium have varied greatly over the years. It has been shown that approximately 50% of patients who form calcium stones also have idiopathic hypercalciuria.4 For this reason, previous recommendations were to consume a low-calcium diet in an effort to reduce the hypercalciuria, which was thought to be a contributing factor to the stone formation.4 However, research has found that calcium restriction is actually associated with an increased risk of stone production.1,4,6,7
In fact, one study found that those with a high calcium intake had a significantly lower risk of stone formation than those with low calcium intake.7 The dietary restriction of calcium has been shown to induce hyperoxaluria, another significant risk factor for stone production. It is thought that the reduced calcium intake decreases the calcium-oxalate binding that occurs in the GI tract, allowing more oxalate to be excreted in the urine, which precipitates stone formation.4,6 Experts are now recommending that calcium-stone-formers consume a normal or increased amount of calcium, with the hypothesis being that this will increase the amount of calcium-oxalate binding in the intestinal lumen, thereby decreasing the amount available in the urinary tract for stone production.2,4,7
Avoid Foods With Oxalate
Oxalate is the second major metabolite found in the common calcium-oxalate stones. There are trace amounts of other minerals in these stones, but the major components are oxalate and calcium, forming at a ratio of 1:5 respectively.4 This ratio is key, indicating that while large increases in calcium are needed to cause stone production, even small increases in urinary oxalate concentrations can create an environment capable of stone formation.4 Research has shown that restricting dietary oxalate has been associated with decreased stone production.1 It is recommended that stone forming patients reduce their intake of oxalate to help prevent kidney stone recurrences.1,2,4 Foods with high amounts of bioavailable oxalate include spinach and rhubarb and should be avoided.1,2,4 Foods such as chocolate, tea, almonds, peanuts and pecans contain a moderate amount of oxalate and should be consumed sparingly.1,2,4
Love that Lemondade
Citrate has a protective effect against kidney stones for patients who have hypocitraturia, which has been shown to be a risk factor for stone production in calcium-stone-formers.1 The physiology behind the protective properties of citrate is not well understood, but studies have shown that both citrate-containing supplements as well as increased natural forms of dietary citrate increase urinary citrate levels, which in turn decreases the incidence of stone production.1 Increased consumption of citrate is therefore recommended for stone-forming patients.1,2 Citrate can be found naturally in citrus foods such as lemons, limes, and tomatoes.1 Increased lemonade consumption has been shown to be an effective method in increasing citrate consumption for the prevention of kidney stones.1 A good ratio to recommend to your patients is 1 cup of lemon juice concentrate per 7 cups of water.2
Stones Love Sodium
The consumption of sodium, which has long been associated with kidney stones, is the basis behind the southern United States getting its “kidney belt” nickname. The effects of sodium on urinary calcium concentrations have been well-studied and demonstrate a strong correlation between the two. For every 100 mmol increase in dietary sodium, urinary calcium excretion increases by 25 mg.4 Increased sodium consumption therefore drives the body into a hypercalciuric state, a known risk factor for kidney stones.4,5 A low-salt diet was found to correct idiopathic hypercalciuria in 30% of cases in a recently conducted, 3-month, randomized controlled trial.5 Beyond its effect on calcium, sodium has also been shown to lower citrate excretion, another risk factor for stone formation4,5. The recommended salt intake for stone-formers should be restricted to less than 2g per day. This can be achieved through the reduction of foods with high salt content (such as canned or processed foods) as well as by eliminating added salt from the diet.2,4,5
Decrease Protein, Especially from Meat
The effects of animal protein consumption has been shown to effect the incidence of kidney stone production, especially for those who form uric acid stones.8 A high intake of animal protein causes a purine overload, which leads to increased amounts of uric acid that is excreted in the urine (hyperuricosuria), thereby increasing the risk for uric acid stones to form.4 The production of calcium-oxalate stones is also affected, to a lesser degree, with animal protein having been reported to increase oxalate synthesis leading to hyperoxaluria, as well as increased absorption of citrate in the kidneys, leading to hypocitraturia.4 Studies have shown a diet with moderate protein restriction reduces all of these stone-forming risk factors.4 It should be recommended to all stone-forming patients to reduce overall protein consumption to less than 30% of their caloric intake, as well as to reduce the amount of animal protein they consume, in an effort to prevent stone recurrence.1,2,4
Personalize the Recommendations
The understanding of dietary influences on kidney stone development has expanded greatly in recent years. While there is a great deal we still don’t understand, we now recognize the importance of nutrition on stone formation. This knowledge allows for improved education and care for patients grappling with the vicious cycle often associated with renal stones. These recommendations were created to improve patients’ quality of life, and should be “personalized” to what works best for each patient. It is important to always take into consideration possible medication interactions, metabolic disorders, and the dietary recommendations for other diseases the patient may have.
1. Barnela S, Soni S, Saboo S, Bhansali A. Medical Management of Renal Stone. Indian J Endocrinol Metab. 2012;16(2): 236-239.
2. Frassetto L, Kohlstadt I. Treatment and Prevention of Kidney Stones: An Update. American Family Physician. 2011;84(11):1234-1242.
3. Ferraro P, Taylor E, Gambaro G, Curhan G. Soda and Other Beverages and the Risk of Kidney Stones. Clin J Am Soc Nephrol. 2013;8(8):1389-1395.
4. Heilberg I. Update on Dietary Recommendations and Medical Treatment of Renal Stone Disease. Nephrol Dial Transplant. 2000;15:117-123.
5. Nouvenne A, Meschi T, Prati B, et al. Effects of a Low-Salt Diet on Idiopathic Hypercalciuria in Calcium-Oxalate StoneFormers: a 3-mo Randomized Controlled Trial. Am J Clin Nutr. 2010;91:565-570.
6. Borghi L, Schianchi T, Meschi T, et al. Comparison of two diets for the prevention of recurrent stones in idiopathic hypercalciuria. The New England Journal of Medicine. 2002;346(2):77-84.
7. Curhan G, Willett W, Rimm E, et al. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. The New England Journal of Medicine.1993;328:833-838.
8. Tracy C, Best S, Bagrodia A, et al. Animal Protein and the Risk of Kidney Stones: A Comparative Metabolic Study of Animal Protein Sources. The Journal of Urology. 2014;192:137-141.