Iron deficiency is a common nutritional problem globally and recent data indicate the prevalence of iron deficiency anemia in the United States is increasing.1 Do soyfoods have a role in countering this trend? Some data suggest yes, but this question can only be definitively answered with more research.
In recently published research by Sun and Weaver, changes in dietary iron intake, serum iron, and serum hemoglobin concentrations were assessed based on data obtained from the laboratory files of NHANES between the years of 1999 and 2018.1 During this same period, iron deficiency anemia–related mortality rates were taken from CDC data and the iron concentrations of U.S. food products were determined based on USDA data.
- Of food items with revised iron concentrations, 62.4% had lower iron concentrations in 1999 compared with 2015.
- There was a 15.3% reduction in beef and a 21.5% increase in chicken meat consumption between 1999 and 2018.
- Dietary iron intake decreased by ∼6% and ∼9.5% for male and female adults, respectively.
- Increases of prevalence of estimated anemia in the United States ranged from 10.5% to 106% depending on age and sex.
- Age-adjusted mortality rates with iron deficiency anemia as the underlying cause of death increased from ∼04 to ∼0.08 deaths per 100,000 people.
- Mean hemoglobin and serum iron concentrations decreased over the past 20 years.
Sun and Weaver1 concluded that the decrease in iron intake largely resulted from the reduction in the iron concentration of U.S. food products. The increasing crop yield over the past decades has been shown to dilute nutrient concentrations.2 In addition, there has been a shift in the U.S. population of meat consumption from primarily beef with relatively higher heme iron concentrations to more poultry meat, primarily chicken, with relatively lower heme iron concentrations. The authors called for efforts to encourage consumption of high-iron diets and discussion on possible policy initiatives to increase the iron concentration in U.S. food products.
As increasing numbers of people adopt a plant-based diet, the intake of bioavailable iron is likely to decrease. Vegetarian, and especially vegan diets, are generally as high in iron as non-vegetarian diets.3,4 However, the issue is not total iron intake, but iron absorption from plant foods. The National Academy of Medicine established a vegetarian RDA, which is 1.8 times higher than the RDA for the general population.5
One of the main dietary inhibitors of iron absorption is phytate, a storage form of phosphorus in plants that inhibits the absorption of divalent cations, such as iron, zinc and calcium.6 For this reason, the recommended zinc intakes established by the European Food Safety Authority are based on the phytate content of the diet (iron intake is not based on phytate content).
However, research published in 2015 showed the chronic consumption of a high-phytate diet mitigated the inhibitory effects of phytate on iron absorption.7 Research aimed at establishing the effect of phytate on mineral absorption typically involves single meal studies. Therefore, phytate may not be as much of an issue as thought for habitual consumers of plant-based diets. On the other hand, vegetarians do typically have lower iron stores than non-vegetarians.8
A look at a selection of soy-based burgers shows their iron content is similar to or higher than the amount of iron found in beef.9 But again, the issue is bioavailability, not content. The traditional thinking is that iron absorption from beans like soy is quite low, but this thinking is based on single meal studies.10 Furthermore, because some of the iron in soy, as well as other legumes, is in the form of ferritin, iron absorption may be much higher than previously thought. Older methodology is not well suited for measuring iron absorption from ferritin. Studies published in 2003 and 2006, using methodology suitable for measuring iron ferritin absorption, showed absorption from soy to be quite high.11,12 However, since those studies were published, no additional research specifically measuring iron absorption from ferritin in soy were identified. Therefore, more research is needed before any firm conclusions can be made. However, much of the iron in one popular soy burger comes from heme (leghemoglobin, legume hemoglobulin), so independent of the ferritin question, one can expect the iron from this soy burger to be well absorbed.13
- Sun H, Weaver CM. Decreased iron intake parallels rising iron deficiency anemia and related mortality rates in the US population. J Nutr. 2021;151:1947-55.
- Sun H, Weaver CM. Rise in potassium deficiency in the US population linked to agriculture practices and dietary potassium deficits. J Agric Food Chem. 2020;68:11121-7.
- Melina V, Craig W, Levin S. Position of the Academy of Nutrition and Dietetics: Vegetarian diets. Journal of the Academy of Nutrition and Dietetics. 2016;116:1970-80.
- Rizzo NS, Jaceldo-Siegl K, Sabate J, et al. Nutrient profiles of vegetarian and nonvegetarian dietary patterns. Journal of the Academy of Nutrition and Dietetics. 2013;113:1610-9.
- Food and Nutrition Board, Institute of Medicine. Iron. In: Dietary References Intake for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium and Zinc. Washington, DC: The National Academies Press; 2001:290-393.
- Gibson RS, Raboy V, King JC. Implications of phytate in plant-based foods for iron and zinc bioavailability, setting dietary requirements, and formulating programs and policies. Nutr Rev. 2018;76:793-804.
- Armah SM, Boy E, Chen D, et al. Regular consumption of a high-phytate diet reduces the inhibitory effect of phytate on nonheme-iron absorption in women with suboptimal iron stores. J Nutr. 2015;145:1735-9.
- Pawlak R, Berger J, Hines I. Iron status of vegetarian adults: A review of literature. Am J Lifestyle Med. 2018;12:486-98.
- Curtain F, Grafenauer S. Plant-based meat substitutes in the flexitarian age: An audit of products on supermarket shelves. Nutrients. 2019;11.
- Lynch SR, Beard JL, Dassenko SA, et al. Iron absorption from legumes in humans. Am J Clin Nutr. 1984;40:42-7.
- Murray-Kolb LE, Welch R, Theil EC, et al. Women with low iron stores absorb iron from soybeans. Am J Clin Nutr. 2003;77:180-4.
- Lonnerdal B, Bryant A, Liu X, et al. Iron absorption from soybean ferritin in nonanemic women. Am J Clin Nutr. 2006;83:103-7.
- Proulx AK, Reddy MB. Iron bioavailability of hemoglobin from soy root nodules using a Caco-2 cell culture model. J Agric Food Chem. 2006;54:1518-22.
This blog sponsored by the Soy Nutrition Institute and the United Soybean Board.