As with any diet that excludes certain food groups, there is a concern that nutritional deficiencies could develop. In the case of vegetarianism, the micronutrients of concern are the ones that occur primarily in animal products, such as iron, zinc, and vitamin B12.[1]
Low iron levels are more common in vegetarians, especially in premenopausal women.[2][3] Meat contains heme iron, but plant foods contain non-heme iron, which is more difficult for the body to absorb. Eating plant sources of iron together with sources of vitamin C may improve absorption. While iron stores might be lower, the prevalence of iron deficiency anemia is not higher in vegetarians, suggesting that the low stores are not necessarily a problem.[4][3] It could be worth monitoring iron levels in some cases, such as children and during pregnancy.[4]
Another concern is zinc. In omnivorous diets, the majority of the zinc intake comes from meat, especially from beef. When eating a vegetarian diet, it is possible to get a similar zinc intake through legumes, whole grains, nuts, and seeds, but this requires careful planning.[4][5] However, so far there is no clear evidence that the lower zinc intake associated with a vegetarian diet causes any long term health concerns.[6]
Vitamin B12 is less of a concern for vegetarians than for vegans, because dairy products and eggs contain a substantial amount of vitamin B12, but vitamin B12 deficiency is still more common among vegetarians than people who eat an omnivorous diet.[7] Including foods fortified with vitamin B12, such as cereals and grains, can help increase the daily vitamin B12 intake. In some cases, a supplement might be necessary. Monitoring or supplementing vitamin B12 is especially important during pregnancy and for early childhood development.[8]