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Examining the Oxalate Content of Soymilk

Examining the Oxalate Content of Soymilk

Last year, a blog post on soymilk and kidney stones included a table on the oxalate content of plant milks. Soymilk was listed as containing 9.6mg per serving (cup). According to the Academy of Nutrition and Dietetics, foods containing >10mg oxalate/serving are classified as high-oxalate foods and should be limited in the diets of people at risk of developing kidney stones. That 9.6mg figure came from a 2021 publication.1 But according to WebMD, soymilk contains 336mg oxalate per cup. These dramatically different estimates make it difficult for people following a low-oxalate diet to know whether or not they can consume soymilk.

It is not surprising to see some variation in estimates of the oxalate content of soymilk. Differences in oxalate values for a single food may be due to biological variation attributed to cultivar, time of harvest, and growing conditions, as well as analytical differences.2  In addition, the manufacturing process may affect oxalate content, so different soymilk brands may contain different amounts of oxalate. However, manufacturing differences cannot explain one milk containing 35x more oxalate than another. There is, however, an even more surprising twist to this seemingly puzzling story.

That 336mg figure on WebMD was likely derived from a 2001 paper by Massey and colleagues3 published in the Journal of Agricultural and Food Chemistry. Although now retired, Dr. Linda Massey was well known for her work in this area. Four years after the 2001 paper, Massey was the senior author of a paper published in the same journal, with 2 of the same authors from the 2001 paper, that listed the oxalate content of 2 soymilks as 5.86 and 5.18mg per serving.4  In the 2005 paper, the authors did not mention in the discussion section that values for soymilk were previously shown by them to be about 62x higher.

The 3 different soymilks (1 in 2001 and 2 in 2005) that were analyzed are all made using whole soybeans and contain roughly the same amount of protein. Could differences in the cultivar of soybeans used for these milks account for some of these differences in the oxalate content of soymilk? Perhaps somewhat, but it is certainly not going to be a major factor base. Horner et al.,5 found that the oxalate content of 116 cultivars of soybeans ranged from 82.3 to 213.6 mg per 100g, about a 2.6-fold variation.

Additional insight about the oxalate content of soy comes from a 2015 paper by Ellis and Lieb,6 who reported values of approximately 5.3mg and 4.0mg per cup for 2 different soymilks. Importantly, one of those soymilks was the same brand of soymilk for which Massey et al. 3 (in their 2001 paper) assigned a value of 336mg. Finally, Harvard T.H. Chan School of Public Health Nutrition Department lists soymilk as containing only 4mg oxalate per cup whereas the Kidney Dietitian lists soymilk as containing 20mg. However, neither source indicated the basis (e.g., a peer-reviewed journal article) for these estimates; therefore, their contribution to our understanding is somewhat limited. On the other hand, these estimates are clearly unsupportive of the value reported by WebMD.

Finally, the 2001 paper listed 4 different tofu products as containing between 43 and 235mg oxalate per serving3 whereas the 2005 paper.4 examined 22  types of tofu of which only 1 contained >10 mg/serving. Therefore, considerable evidence indicates that an oxalate value of 336mg for soymilk is incorrect, and furthermore, that soymilk is a food that can be consumed by people at risk of developing kidney stones.

References

  1. Borin JF, Knight J, Holmes RP, Joshi S, Goldfarb DS, Loeb S. Plant-based milk alternatives and risk factors for kidney stones and chronic kidney disease. J Ren Nutr 2021.
  2. Massey LK. Food oxalate: factors affecting measurement, biological variation, and bioavailability. J Am Diet Assoc 2007;107:1191-4.
  3. Massey LK, Palmer RG, Horner HT. Oxalate content of soybean seeds (Glycine max: Leguminosae), soyfoods, and other edible legumes. J Agric Food Chem 2001;49:4262-6.
  4. Al-Wahsh IA, Horner HT, Palmer RG, Reddy MB, Massey LK. Oxalate and phytate of soy foods. J Agric Food Chem 2005;53:5670-4.
  5. Horner HT, Cervantes-Martinez T, Healy R, Reddy MB, Deardorff BL, Bailey TB, Al-Wahsh I, Massey LK, Palmer RG. Oxalate and phytate concentrations in seeds of soybean cultivars [Glycine max (L.) Merr.]. J Agric Food Chem 2005;53:7870-7.
  6. Ellis D, Lieb J. Hyperoxaluria and genitourinary disorders in children ingesting almond milk products. J Pediatr 2015;167:1155-8.

 This blog is sponsored by SNI Global and the United Soybean Board.

Dr. Mark Messina

Author Dr. Mark Messina

PhD in Nutrition, Director of Nutrition Science and Research, Soy Nutrition Institute Global. Expert in soyfoods and isoflavones.

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