Protein: Critics of vegetarianism commonly believe that vegetarians are protein deficient. However, vegetarians who consume legumes, whole grains, nuts, and seeds get enough protein. By including a variety of foods from each of these categories, and by properly combining these foods, vegetarians can get all of the essential amino acids (protein building blocks that must be obtained from the diet). In addition, vegetarians who supplement their plant-based diet with dairy, eggs, or fish add complete protein (providing all of the essential amino acids) through these foods.
Vitamin B12: Vitamin B12 is a nutrient found mainly in animal foods, including dairy, eggs, and fish, which are part of some vegetarian diets. Certain plant foods, like seaweeds (especially nori) and mushrooms, are also good sources. The bacteria involved in fermentation and culturing contribute B12 to foods like tofu, miso, tempeh, natto, kimchi, and sauerkraut. Despite all of these B12 sources, studies find that many vegetarians are B12 deficient, so a supplement is generally a good idea.
Calcium and Vitamin D: Some critics fault vegetarian diets for not providing sufficient calcium and vitamin D; however, researchers have found that vegetarians are no more likely to be deficient in these important nutrients than omnivores. This may be because most people who consider themselves vegetarian still consume dairy products. Vegans, who do not consume dairy foods, don’t get as much dietary calcium and vitamin D as vegetarians or omnivores.
Iron: Vegetarians get most of their iron from legumes and leafy green vegetables, with nuts, seeds, whole grains, and dried fruit contributing smaller amounts. Even though the non-heme iron found in plants is harder to absorb than heme iron from meat, poultry, and fish, vegetarians appear to have no higher risk of iron deficiency anemia than non-vegetarians, and may even be protected from the harmful effects of excess iron.
Zinc: While omnivores get zinc from meat and poultry, vegetarians rely on plant sources like nuts, seeds, legumes, and oatmeal, and any dairy, eggs, or fish they choose to include. Vegetarians typically need more dietary zinc than non-vegetarians, since the legumes and grains they rely on are high in phytates, compounds that can bind to zinc and prevent its absorption. Soaking, sprouting, and leavening (as with yeast) are strategies that can improve the availability of zinc in legumes and seeds.
Iodine: Critics of vegetarians who don’t eat fish say that by not getting enough iodine, and by consuming large amounts of anti-thyroid chemicals from soybeans and cabbage, broccoli, kale and related vegetables, they put themselves at risk for thyroid disorders. A study comparing vegans, vegetarians, and omnivores found that vegetarians were no more likely to be iodine deficient or have thyroid problems than non-vegetarians. Vegetarians who don’t eat fish still get iodine from seaweed, sea salt, and iodized salt.