Nutrition

New Dietary Guidelines Say Soymilk Only Suitable Alternative to Cow’s Milk

New Dietary Guidelines Say Soymilk Only Suitable Alternative to Cow’s Milk

Over the past decade there has been rigorous discussion of the role of non-dairy plant milks (NDPM) in the diet. Many reviews comparing the nutrient content of NDPM with cow’s milk have been published in recent years.1-5 Even the nomenclature used to describe NDPM has become the subject of intense debate, with efforts being put forth to restrict the term “milk” to the liquid that comes from a mammal, not a plant.  Recent commentaries/reports have been raised about children replacing cow’s milk with NDPM.6-8

In considering the health attributes of NDPM it is critical to recognize that the vast array of commercially available non-dairy milks derived from plants differ nutritionally from one another and that marked differences can exist even among milks derived from the same plant. The former point is illustrated by the recently released 2020-2025 U.S. Dietary Guidelines. Fortified soymilk was singled out as the only NDPM that can serve as an alternative to cow’s milk.9

Debate about NDPM is understandable given the role that cow’s milk has traditionally played in the diets of children in Western populations. Current recommendations are for children 12 to 24 months to consume 2-3 cups of whole milk per day and for children 2-3 and 4-5 years of age to consume up to two cups and up to 2.5 cups per day of skim or low-fat milk, respectively.8

Milk is the number one source of energy, calcium, vitamin A, vitamin D, and zinc for infants and young children. Milk is a source of those nutrients in part because of the amount of milk that is consumed. A recent U.S. survey found that among 12 to 23.9-month-olds, the most commonly consumed beverage was whole milk (67% consuming) and among 12 to 47.9-month-olds, milk provided more energy than all other beverages.10

Milk is best known for the protein, calcium, and vitamin D it provides. One of the reasons that soymilk has been designated as the only plant-based alternative to cow’s milk is because its protein content is similar to cow’s milk. However, a 2021 viewpoint published in JAMA Pediatrics included the statement that “soy has the highest protein content of plant-based beverages, but its reduced protein bioavailability is a serious concern.”6

The reference cited in support of this statement lists soymilk as containing 2.9g vs. 3.3g/100g protein for cow’s milk. No reference in this paper was made to protein quality, so it is not clear to what “reduced bioavailability” refers other than reduced protein content. However, the difference between the two milks would result in soymilk providing only 1g less protein per serving than cow’s milk. Furthermore, the USDA database includes soymilks that provide ≥8g protein per serving (e.g., FDC ID: 1357686) and a comprehensive review on the content of NDPM lists soymilk as containing 8.71g/serving (240ml).1

Regarding protein quality, it is established that the soy protein ingredients (soy protein isolate and soy protein concentrate) qualify as high-quality proteins,11 according to the USDA threshold of a protein digestibility corrected amino acid score of ≥0.8.12 Limited work on the quality of protein from soymilk has been conducted, but last year French researchers reported a digestible indispensable amino acid score for soymilk of 99% using the scoring pattern for a child 6 months to 3 years of age, and 117%, when using the pattern for the older child, adolescent, and adult.13

As noted, another key ingredient in cow’s milk is calcium. Most NDPM on the market are fortified with this mineral. However, in its position paper on NDPM, the North American Society for Pediatric Gastroenterology, Hepatology, raised the issue of calcium bioavailability.7 Studies have shown the calcium from soymilk is well-absorbed, although absorption will vary according to the calcium fortificant.14-16 Note also that some soymilks contain more calcium than cow’s milk (300mg/240ml).1,7

Most soymilks, like cow’s milk, are fortified with vitamin D. In the case of soymilk and NDPM, the vitamin D is typically ergocalciferol (vitamin D2), whereas for cow’s milk, it is cholecalciferol (vitamin D3). The latter may be more effective than vitamin D2 at increasing blood levels of 25-hydroxyvitamin D.17 Whether differences exist between the two forms of vitamin D with chronic consumption remains to be determined.

Finally, cow’s milk can be an important source of iodine, especially in countries that do not fortify table salt with this mineral.18 In contrast, NDPM is low or devoid of this mineral unless fortified, which is generally not the case.19-21 Iodine status in the United States is quite good according to recent NHANES data.22 However, little is known about the iodine nutriture of consumers of NDPM. In the United Kingdom, iodine status (as assessed by 24-hour iodine excretion) was lower in consumers of soymilk in women of childbearing age. But this study included only 5 women who drank soymilk.23 Furthermore, in contrast to the British study,23 a U.S. study found higher urinary iodine concentrations (indicating higher iodine intake) were associated with recent ingestion of soymilk in vegetarians.24

In conclusion, because the nutrient profile of NDPMs differ, it is difficult to generalize about their nutritional attributes. Soymilk provides high-quality protein in amounts similar to cow’s milk and contains well-absorbed calcium. It is the only NDPM identified by the U.S. Dietary Guidelines as a suitable alternative to cow’s milk.

References

  1. Vanga SK, Raghavan V. How well do plant based alternatives fare nutritionally compared to cow’s milk? Journal of food science and technology. 2018;55:10-20.
  2. Angelino D, Rosi A, Vici G, et al. Nutritional quality of plant-based drinks sold in Italy: The food labelling of Italian products (FLIP) study. Foods. 2020;9.
  3. Scholz-Ahrens KE, Ahrens F, Barth CA. Nutritional and health attributes of milk and milk imitations. Eur J Nutr. 2020;59:19-34.
  4. Singhal S, Baker RD, Baker SS. A comparison of the nutritional value of cow’s milk and nondairy beverages. J Pediatr Gastroenterol Nutr. 2017;64:799-805.
  5. Vitoria I. The nutritional limitations of plant-based beverages in infancy and childhood. Nutr Hosp. 2017;34:1205-14.
  6. Bodnar LM, Jimenez EY, Baker SS. Plant-based beverages in the diets of infants and young children. JAMA Pediatr. 2021.
  7. Merritt RJ, Fleet SE, Fifi A, et al. North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition Position Paper: Plant-based Milks. J Pediatr Gastroenterol Nutr. 2020;71:276-81.
  8. Lott M, Callahan E, Welker Duffy E, et al. Healthy beverage consumption in early childhood: Recommendations from key national health and nutrition organizations. Consensus statement (available at http://healthyeatingresearch.org). In. Durham, NC: Healthy Eating Research; 2019.
  9. U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020-2025. 9th Edition. December 2020. Available at DietaryGuidelines.gov.
  10. Kay MC, Welker EB, Jacquier EF, et al. Beverage consumption patterns among infants and young children (0-47.9 months): Data from the feeding infants and toddlers study, 2016. Nutrients. 2018;10.
  11. Hughes GJ, Ryan DJ, Mukherjea R, et al. Protein digestibility-corrected amino acid scores (PDCAAS) for soy protein isolates and concentrate: Criteria for evaluation. J Agric Food Chemistry. 2011;59:12707-12.
  12. www.fns.usda.gov/questions-and-answers-alternate-protein-products-app.
  13. Reynaud Y, Buffiere C, Cohade B, et al. True ileal amino acid digestibility and digestible indispensable amino acid scores (DIAASs) of plant-based protein foods. Food Chem. 2020;338:128020.
  14. Heaney RP, Dowell MS, Rafferty K, et al. Bioavailability of the calcium in fortified soy imitation milk, with some observations on method. Am J Clin Nutr. 2000;71:1166-9.
  15. Zhao Y, Martin BR, Weaver CM. Calcium bioavailability of calcium carbonate fortified soymilk is equivalent to cow’s milk in young women. J Nutr. 2005;135:2379-82.
  16. Tang AL, Walker KZ, Wilcox G, et al. Calcium absorption in Australian osteopenic post-menopausal women: an acute comparative study of fortified soymilk to cows’ milk. Asia Pacific journal of clinical nutrition. 2010;19:243-9.
  17. Tripkovic L, Wilson LR, Hart K, et al. Daily supplementation with 15 mug vitamin D2 compared with vitamin D3 to increase wintertime 25-hydroxyvitamin D status in healthy South Asian and white European women: a 12-wk randomized, placebo-controlled food-fortification trial. Am J Clin Nutr. 2017;106:481-90.
  18. Hemken RW. Factors that influence the iodine content of milk and meat: a review. J Anim Sci. 1979;48:981-5.
  19. Bath SC, Hill S, Goenaga Infante H, et al. Iodine concentration of milk-alternative drinks available in the UK in comparison with cows’ milk. Br J Nutr. 2017:1-8.
  20. Ma W, He X, Braverman L. Iodine content in milk alternatives. Thyroid. 2016;26:1308-10.
  21. Crawford BA, Cowell CT, Emder PJ, et al. Iodine toxicity from soy milk and seaweed ingestion is associated with serious thyroid dysfunction. Med J Aust. 2010;193:413-5.
  22. Caldwell KL, Miller GA, Wang RY, et al. Iodine status of the U.S. population, National Health and Nutrition Examination Survey 2003-2004. Thyroid. 2008;18:1207-14.
  23. Bath SC, Sleeth ML, McKenna M, et al. Iodine intake and status of UK women of childbearing age recruited at the University of Surrey in the winter. Br J Nutr. 2014;112:1715-23.
  24. Leung AM, Lamar A, He X, et al. Iodine status and thyroid function of Boston-area vegetarians and vegans. J Clin Endocrinol Metab. 2011;96:E1303-7.
Dr. Mark Messina

Author Dr. Mark Messina

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

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