Written by Henry Lin and Edited by Alexander Alva
Kidney stones is an umbrella term that refers to the different types of hard crystals that are formed by certain ions that combine in the kidneys. From there, the crystals may travel out of the kidneys and into the rest of the urinary tract, where they could lodge themselves into tissue and cause intense pain [1]. Such pain usually resides along the lower back and sides of the body and can be accompanied by symptoms, including blood in the urine and vomiting [1]. As kidney stones can be unpleasant and painful, there are many things one can do to decrease the likelihood of developing kidney stones—the most notable being a change in diet.
The two most common types of kidney stones are calcium oxalate stones and uric acid stones [1]. Calcium oxalate stones form from the combination of calcium and oxalate ions in urine, whereas uric acid stones form from high concentrations of uric acid, a chemical product formed from the metabolism of purine derived from organ meats and shellfish [1]. Therefore, recommendations to prevent the risk of developing kidney stones include limiting excessive intake of foods, such as shellfish and organ meats, that can contribute to the growth of these stones [1].
Furthermore, the first step to a beneficial diet is to consider increasing one’s daily water intake. Kidney stones begin to form when urine becomes supersaturated, and as a result, ions start to crystallize out of the urine that lead to kidney stone formation [2]. However, increasing water intake increases the solubility of the ions in urine, thus preventing them from crystallizing into kidney stones [2]. Therefore, it is recommended to consume at least 2.5-3 liters of water throughout an entire day to keep those ions soluble in urine [3]. It is important to note that increasing water intake refers specifically to water only and not other beverages such as caffeine, black tea, and juices. Such beverages will instead increase the amount of ions in urine and saturate it further—leading to increased kidney stone development [2].
Along with increasing water intake, sodium intake should be limited as a means of reducing the risk of kidney stone development. In the kidneys, sodium ions compete with stone-forming ions like calcium for reabsorption. As a result, an increase in sodium ion concentration will outcompete the calcium ions, resulting in a higher concentration of calcium ions in the urine that contribute to stone formation [2]. Sodium intake is recommended to be limited to only 2,000 milligrams (mg) per day, but the exact value may differ for each individual [3].
Since a high concentration of calcium ions in urine is correlated with higher risks of calcium oxalate stone formation, one may make the misconception that limiting calcium intake may reduce the development of such stones; however, this is actually counterintuitive. The restriction of calcium intake can actually increase risk of kidney stones as well as lead to other undesirable side effects, such as osteoporosis, a bone disease [4]. On the other hand, studies have shown the association of consuming a recommended amount of calcium, along with decreased sodium and animal protein intake, with a decrease in the risk of stone formation [2]. This is due to calcium binding with oxalates in the gut to form non-absorbable compounds, resulting in less free oxalates being absorbed into the bloodstream, and thus lowered prevalence of oxalates binding to calcium to form stones in the urinary tract [4]. Therefore, a diet involving the appropriate consumption of low-fat dairy, green leafy vegetables, broccoli, and almonds (foods high in calcium) is recommended [2].
Oxalate ions, the other component of calcium oxalate stones, have a greater role in stone formation than its calcium ion counterpart [2]. Therefore, it is more important to regulate oxalate ion concentration than calcium ion concentration. The simplest way to lower oxalate ion concentration is to limit, but not completely avoid, consumption of foods rich with it, such as chocolate, nuts, beans, rhubarb, spinach, beets, and tea [3]. In addition, Vitamin C intake is recommended to be 1000 mg per day since it is associated with the natural formation of oxalates in the body [3].
Although dietary adjustments may reduce the risk of developing kidney stones, each individual may experience different reactions to a dietary change, so it is important to consult with a medical professional before making an extreme diet transition. In addition, the diets discussed in this article apply mainly to calcium oxalate and uric acid stones, while other kidney stones, such as those associated with genetic disorders, such as Cystinuria (stones caused by buildup of amino acid cysteine) and hereditary xanthinuria (stones caused by build up of xanthine chemical compound), may have other recommended lifestyle changes to prevent the risk of stone formation [5].
References
- “Kidney Stones” (2020). National Kidney Foundation, National Kidney Foundation Inc. Accessed 19 Jan. 2020.
- Krieg, C. (2005). The Role of Diet in the Prevention of Common Kidney Stones. Urologic Nursing, 25:451-456.
- Finkielstein, V.A., Goldfarb, D.S. (2006). Strategies for Preventing Calcium Oxalate Stones. Canadian Medical Association Journal, 170:1407-1409.
- Sorensen, M.D. (2014). Calcium Intake and Urinary Stone Disease. Translational Andrology and Urology, 3:235-240.
- “Kidney Stones” (2020). Medline Plus, U.S. National Library of Medicine. Accessed 27 Jan. 2020.