Vegetarians must choose their foods carefully, since some nutrients are more abundant in animal foods, and others are less bioavailable when consumed from plants. (INFOGRAPHIC 9.7)

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Question 9.6

Protein is one important example. Individuals who eat fish, dairy, or eggs typically don’t have to worry about getting enough complete proteins—proteins that contain all nine essential amino acids in the amount needed to support protein tissue construction. Some plant foods contain all nine essential acids in the ideal proportions, such as soybeans (found in tofu, tempeh, edamame, soy milk, and other soy-based products) and quinoa, the seed of a plant related to spinach. But most plant foods provide incomplete proteins because they do not provide all nine amino acids in the amounts needed to synthesize protein in the body. As a result, vegetarians need to eat complementary protein foods to provide their bodies with sufficient quantities and proportions of the essential amino acids. (INFOGRAPHIC 9.8) Examples of complementary protein foods are beans and grains (such as rice) or beans and most nuts; the two foods contain different amino acids that together provide adequate amounts of all essential amino acids. There is no need to eat the complementary proteins in the same meal, but they should be consumed within the same day as part of an overall balanced and varied diet.

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Question 9.7

Iron is another nutrient of which vegetarians sometimes consume too little. Although iron is found in plant foods in a form called non-heme, it is less bioavailable than the heme iron found in animal foods. (See Chapter 14 for full discussion of heme and non-heme iron.) As a result, the recommended non-heme iron intake for vegetarians, particularly vegans, is 80% higher than the iron recommendation for nonvegetarians. Iron-containing plant foods are soybeans, legumes, dried fruit, as well as fortified grains and cereals.

Zinc, found in soy products, legumes, grains, and nuts, is less well-absorbed from plant foods than it is from animal foods, though vegetarians typically get enough of this mineral. Calcium, vitamin D, and riboflavin (vitamin B₂) are nutrients of concern for vegetarians. Although intake of these nutrients in lacto-ovo vegetarians is similar to intake in nonvegetarians, vegans may fall below recommended intake levels because they avoid dairy products, which are important sources of these nutrients. Vegans can, however, obtain calcium by eating leafy greens and broccoli, and they can get both calcium and vitamin D from milk alternatives such as soy, rice, and almond milks, as well as some other fortified foods and beverages such as orange juice. Riboflavin is found in high amounts in almonds, and moderately high amounts in mushrooms and cooked spinach, and in lower amounts in whole and enriched grains, but supplementation may sometimes be warranted.

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Vitamin B₁₂ is only found in foods of animal origin, and because unfortified plant foods contain no B₁₂, vegans must be careful to obtain it from fortified foods such as soy and rice beverages, certain breakfast cereals and meat analogs (which are often soy-based products), as well as specially fortified nutritional yeasts. If vegans can’t get enough B₁₂ from these sources, a daily vitamin B₁₂ supplement may be necessary. Vegetarians who avoid eating seafood must take care to consume enough iodine by selecting iodized forms of table salt, the primary source of iodine in the U.S. diet.

Finally, vegetarian diets are generally rich in omega-6 fatty acids, but they may be marginal in the omega-3s EPA and DHA, which are found primarily in fish (see Chapter 6). Plant foods do provide the omega-3 ALA (alpha-linolenic acid), but less than 10% of ALA in plant foods is converted to EPA and DHA. EPA and DHA can also be found in foods such as soy milk, margarine, and eggs. Vegetarians who avoid animal sources of DHA and EPA should maximize their intake of ALA through walnuts, flaxseeds, soy, and algae.