Vegetarian Diets and Anemia - A Review of Evidence

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There is a growing trend, particularly among young people, toward adopting a vegetarian or vegan diet. In fact, an article from the Toronto Metro—written by Aly Thompson and published March 13, 2018—reported on a Dalhousie University poll showing that Canadians under 35 years old were “three times more likely to consider themselves vegetarians or vegans than people 49 or older.” ^[1] Some observers of this trend will be concerned about the potential nutritional inadequacies of a vegetarian and perhaps even a vegan diet. They may ask: “Will we end up having a generation of Canadians who are nutritionally deficient?” One such nutrient of concern is iron. Though several nutrients are of concern for vegetarians, this article will focus on this one mineral. This paper will seek to try to bring a different perspective by providing answers to questions such as:

• Are vegetarians deficient in iron intake?
• Will they become anemic?
• Are plant sources of iron less absorbable than animal sources?

These are important questions to answer as we observe these shifts in dietary patterns. We want to prevent having a nutritionally deficient population, but at the same time, our fears and concerns should be based on the evolving science, not traditionally held views.

Less Iron Does Not Mean Deficient in Iron

The body iron stores of vegetarians are typically lower than those of nonvegetarians. ^[2] This may be due to the different types of iron one gets when eating animal foods versus plant foods. Iron from sources like beef and chicken contain what is called heme iron.

Plant sources contain nonheme iron. The heme iron from animal sources is more easily absorbed than the plant-derived nonheme iron. Absorption of heme iron is approximately 15–40%; for nonheme iron, some estimates suggest 1–15% or 1–23% absorption. ^[3][4] However, a very key point to emphasize is that having lower iron stores does not mean having deficient stores, nor does consuming less-absorbable iron mean having a deficiency of iron. Just because a vegetarian eats a less-absorbable form of iron does not mean he or she will be deficient in iron. Nor does having lower body stores of iron equate to being “deficient in iron”; it just means the stores of iron in vegetarians are typically lower than those of nonvegetarians. The Dietitians of Canada acknowledged this in their position paper by stating: “Incidence of iron deficiency anemia among vegetarians is similar to that of nonvegetarians. Although vegetarian adults have lower iron stores than nonvegetarians, their serum ferritin levels are usually within the normal range.” ^[5] The Academy of Nutrition and Dietetics’ position paper on vegetarian diets also supports the notion that vegetarians are not necessarily deficient in iron: “The absorption process appears to adapt effectively in the case of Western vegetarians because their hemoglobin values and most other measures of iron status are similar to those values seen in nonvegetarians.” ^[4]

Body Efficient at Regulating Plant-Sourced Iron Absorption

The absorption of iron from animal sources (heme iron) is not very sensitive to the levels of iron already stored in the body. However, it is known that the body can regulate the absorption of plant-based iron (nonheme) very well, based on the levels of iron already stored in the body. When it has low stores, it will upregulate the absorption of iron. When the storage levels are high, it will downregulate iron absorption. ^[4] In one study, researchers found that vegetarian subjects were able to adapt their iron absorption based on their iron status. ^[2] The vegetarian subjects also excreted less ferritin in their feces as well. One scientist sums up this physiological process by stating: “[…] although plant-based diets contain a greater proportion of the generally lesswell absorbed nonheme iron, this form is more responsive to differences in body iron status. This conveys the advantage that nonheme iron absorption can be more completely limited by those with high iron stores, while being nearly as well absorbed as heme iron by those with low iron stores.” ^[3] The Academy of Nutrition and Dietetics makes a similar point: “Non-heme iron absorption depends upon physiological need and is regulated in part by iron stores. Its absorption can vary depending upon both the meal composition and the iron status of the individual.” ^[4]

This ability to regulate the absorption of nonheme iron based on already-existing bodystorage levels may partly explain why vegetarians and potentially vegans may still have normal iron levels despite eating a less-absorbable form of the mineral. This is recognized by a group of researchers who state in their paper: “Adaptive control of absorption may explain why vegetarians often have lower iron stores than nonvegetarians but not iron deficiency. Although the current study indicates much less iron absorption from a lactoovovegetarian diet than from a nonvegetarian diet, the serum ferritin concentrations and other iron indexes do not justify concern about the iron status of vegetarians without evidence of a greater iron deficiency.” ^[2] So, one can see that the situation with iron is like that of protein. Beef, chicken, fish, and goat may provide a more absorbable iron as they do more bioavailable protein; however, this does not mean that a diet lacking in these flesh foods will automatically mean one will be either deficient in their intake of iron or deficient in their body stores of iron. To say to the contrary would be a false assumption for which there is little evidence in support.

Vegetarians Can Eat Enough Iron in Their Diet

Another important question to settle: “Do vegetarians consume enough total iron?” This is an important question because, though the body has the ability to regulate the absorption of plant-based iron very well, one must still consume enough iron to meet the body’s needs. The evidence suggests that vegetarians can consume enough iron. A study done on a cohort of over 71,751 subjects revealed that nonvegetarians, semivegetarians, pescovegetarians, lactoovovegetarians, and strict vegetarians had no significance difference in the iron content of their diets; their meal compositions were similar in the amount of iron. ^[6] More specifically, lactoovovegetarians were consuming about 34.1 mg of iron per day, and strict vegetarians were consuming 31.6 mg of iron per day. ^[6] The Dietitians of Canada recommend men older than 19 years of age to consume a minimum of 8 mg per day, and women between 19 and 50 years of age to consume 18 mg per day. ^[7] For women 51 and older, the amount is the same as for men (8 mg per day). As can be clearly seen then, in the above study, even the strict vegetarians were consuming well above the amount of iron recommended by the Dietitians of Canada. This strengthens an assertion made by the Academy of Nutrition and Dietetics position paper that: “Vegetarians generally consume as much iron as or slightly more than omnivores.” ^[4] These are truly important insights given the often-false statements people make about turning more plant-based. Statements like: “You will become iron deficient” or cynical questions such as: “Where are you going to get your iron?” are uncalled for. Even insinuating that an individual may become anemic because their plant-sourced iron is less absorbable, is also misleading. Even when it comes to vegan diets, the Dietitians of Canada state: “A healthy vegan diet can meet all your nutrient needs at any stage of life including when you are pregnant, breastfeeding or for older adults.” ^[8]

Inhibitors and Enhancers

Another challenge may come from those who point to the decreased levels of iron absorption enhancers and the increased levels of inhibitors in vegetarian diets compared to nonvegetarian diets. So, iron-absorption inhibitors and enhancers need to be addressed as well. Nutrients like vitamin C and unidentified factors in meat seem to enhance the absorption of iron. ^[3]Substances like phytate; certain proteins in soy; and polyphenols like tannic and chlorogenic acids found in tea, coffee, and red wine, seem to be inhibitors of iron absorption. ^[3] Vegetarian diets may be higher in these inhibitors and lower in enhancers than a typical omnivorous diet.

However, one must be careful of the conclusions that are drawn from this information. First, there is evidence to suggest that the magnitude of the effect of enhancers and inhibitors on iron absorption may diminish over time.[4] What does this mean? When initially adopting a vegetarian diet, the change in the number of enhancers and inhibitors one is eating may have an impact, but then eventually the body adapts. Also, does ingesting more inhibitors and less enhancers mean a vegetarian will necessarily become iron-deficient? Ingesting more inhibitors does not doom one to become deficient, nor does ingesting less enhancers lead to the same. Even the combination of those two does not necessarily result in a deficiency. In fact, as stated above, there is little evidence that vegetarians will be iron-deficient.

Some Qualifiers

Given the perspectives offered in this article, some qualifiers do need to be stated so as to present a balanced presentation of the subject. Despite the information stated above, this does not mean that all vegetarians are perfect at getting their iron intake right. Many may become deficient if they do not follow their vegetarian diets correctly. Thus, the argument is not to silence any conversation between patients and their health professional regarding iron intakes in relation to a vegetarian diet. However, a sweeping generalization that vegetarians will be iron-deficient is not warranted, and it would be irresponsible to try to deter people from turning to a vegetarian diet by exaggerating the concern of becoming anemic.

Conclusion

This paper did not go into providing specific advice on how to obtain enough iron; however, it did seek to answer various questions surrounding whether a vegetarian will become anemic. It is the conclusion of this paper that a vegetarian diet should provide an adequate amount of iron when followed properly. Becoming fully vegan or vegetarian, or simply going more “plant-based,” are trends occurring among Canadians. Such a shift may raise concerns regarding iron deficiency among vegetarians. However, when providing education about the risks of iron deficiency, one must state the facts and not present outdated information based on how things have traditionally been understood.