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Soymilk and Kidney Stones

Soymilk and Kidney Stones

Nephrolithiasis, or kidney stones, is the presence of renal calculi caused by a disruption in the balance between solubility and precipitation of salts in the urinary tract and in the kidneys.  Approximately 10% of people participating in the 2013–2014 National Health and Nutrition Examination reported having kidney stones. The highest prevalence was observed in males older than 60 years, at 17.8%, followed by males 40–59 years old at 12.6%.1  Diet plays a huge role in the prevention and management of kidney stones.2

A recent publication by Borin et al.3 concluded that “oat, macadamia, rice, and soy milk compare favorably in terms of kidney stone risk factors with dairy milk, whereas almond and cashew milk have more potential stone risk factors.” Let us take a look at the various dietary factors that impact kidney stone risk and the composition of plant milks.

Kidney stones are commonly comprised of calcium oxalate, so some authorities recommend limiting oxalate intake to no more than 50mg per day.2 As shown in the table below, six plant milks contain fewer than 10mg oxalate per cup whereas two are quite a bit higher. However, because research shows that a high oxalate diet is not associated with increased risk of kidney stones in the general population4 and the amount of oxalate consumed does not necessarily translate to oxalate in the urine,5,6 oxalate intake is not the focus it once was. Nowadays, recommendations often call for avoiding the consumption of high-oxalate foods. High-oxalate foods include spinach (970mg/100g), rhubarb (800mg/100g), almonds (469mg/100g), and collards (450mg/100g).

Dietary sodium restriction decreases urinary calcium excretion7,8 so recommendations are to limit sodium intake to no more than 3g/d.2 In comparison to cow’s milk, three plant milks (flax, almond and hemp) contain more sodium than milk, four contain similar amounts (oat, rice, macadamia, and hazelnut), one is moderately lower (soymilk) and two contain much less (coconut and cashew).

Observational studies show inverse associations between dietary potassium intake and risk of kidney stones.9,10 Plus, potassium is a shortfall nutrient in the U.S., and dairy products are a major source of this mineral.11 Only two plant milks, soymilk and oat milk, contain similar levels of potassium as cow’s milk.

The publication by Borin et al.3 did not provide information about the protein content of the plant milks they discussed. High protein diets increase hypercalciuria, lower urine pH, and increase uric acid levels, all of which increase kidney stone risk.12 Nevertheless, protein recommendations are to consume between 0.8 and 1.4g/kg body weight.2 Therefore, the protein content of the plant milks is an important consideration. Only soymilk contains protein in amounts equal to that of cow’s milk.

Finally, at one point, recommendations were to consume low-calcium diets because most kidney stones contain calcium. However, it is now recognized that because calcium can bind oxalate, high-calcium diets are independently associated with a lower risk of developing kidney stones.13 However, for calcium to exert this protective effect, calcium and oxalate should be consumed at the same meal. Most plant milks are calcium-fortified, so they contain similar amounts of calcium as cow’s milk.

When considering the kidney stone risk factors and overall nutrient content, an argument can be made that soymilk most closely approximates cow’s milk.  This conclusion is consistent with the 2020-2025 U.S. Dietary Guidelines that note soymilk as the only plant milk that is a nutritionally adequate substitute for cow’s milk.

Nutrient content per cup of cow’s milk and selected plant milks

MilkSodium

(mg)

Calcium

(% RDA)

Potassium

(mg)

Oxalate

(mg)

Protein

(g)

Almond15030027.11
Cashew1029417.22
Hazelnut11510NS11.31
Soymilk90303809.66.34
Hemp130201454.53
Oat100253903.53
Macadamia11535101.11
Rice10030650.710.7
Flax1902520<0.430
Coconut25100<0.430.5
Dairy120303800.548

Note that except for protein, data come from Borin et al. paper. Protein comes from U.S. Department of Agriculture, Agricultural Research Service. FoodData Central, 2019. fdc.nal.usda.gov.

References

  1. Chen Z, Prosperi M, Bird VY. Prevalence of kidney stones in the USA: The National Health and Nutrition Evaluation Survey. J Clinical Urol. 2019;12:296-302.
  2. Han H, Segal AM, Seifter JL, et al. Nutritional management of kidney stones (nephrolithiasis). Clin Nutr Res. 2015;4:137-52.
  3. Borin JF, Knight J, Holmes RP, et al. Plant-based milk alternatives and risk factors for kidney stones and chronic kidney disease. J Ren Nutr. 2021.
  4. Taylor EN, Curhan GC. Oxalate intake and the risk for nephrolithiasis. J Am Soc Nephrol. 2007;18:2198-204.
  5. Massey LK, Roman-Smith H, Sutton RA. Effect of dietary oxalate and calcium on urinary oxalate and risk of formation of calcium oxalate kidney stones. J Am Diet Assoc. 1993;93:901-6.
  6. Taylor EN, Curhan GC. Determinants of 24-hour urinary oxalate excretion. Clin J Am Soc Nephrol. 2008;3:1453-60.
  7. Nouvenne A, Meschi T, Guerra A, et al. Dietary treatment of nephrolithiasis. Clin Cases Miner Bone Metab. 2008;5:135-41.
  8. Nouvenne A, Meschi T, Prati B, et al. Effects of a low-salt diet on idiopathic hypercalciuria in calcium-oxalate stone formers: a 3-mo randomized controlled trial. Am J Clin Nutr. 2010;91:565-70.
  9. Curhan GC, Willett WC, Rimm EB, et al. A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. N Engl J Med. 1993;328:833-8.
  10. Curhan GC, Willett WC, Speizer FE, et al. Comparison of dietary calcium with supplemental calcium and other nutrients as factors affecting the risk for kidney stones in women. Ann Intern Med. 1997;126:497-504.
  11. Hess JM, Cifelli CJ, Agarwal S, et al. Comparing the cost of essential nutrients from different food sources in the American diet using NHANES 2011-2014. Nutrition journal. 2019;18:68.
  12. Kok DJ, Iestra JA, Doorenbos CJ, et al. The effects of dietary excesses in animal protein and in sodium on the composition and the crystallization kinetics of calcium oxalate monohydrate in urines of healthy men. J Clin Endocrinol Metab. 1990;71:861-7.
  13. Taylor EN, Curhan GC. Dietary calcium from dairy and nondairy sources, and risk of symptomatic kidney stones. J Urol. 2013;190:1255-9.
Dr. Mark Messina

Author Dr. Mark Messina

PhD in Nutrition, Executive Director, Soy Nutrition Institute. Expert in soyfoods and isoflavones.

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