Most plant derived foods do not contain vitamin B12 and are low in methionine, iron, zinc, vitamin A, and vitamin B6. These deficiencies are particularly damaging during the periods of rapid growth and physiological stress, such as the neonatal period throughout adolescent growth spur, pregnancy, nursing, older age, and various wasting diseases. Vitamin B12 is synthesized by bacteria, many unicellular fungi and algae, but not by animals and higher plants. Vegans are particularly at risk of developing neurological damage from B12 deficiency, because many vegetarian diets have a high folic acid content, which can mitigate the anemic development but let the less noticeable neurological damage to proceed. Vegans are also at higher risk of vitamin A deficiency.
Leafy vegetables contain abundant amounts of provitamins A, e.g., beta-carotene.
Thus, vegetarians are urged to consume dark colored leafy vegetables with some fat, also inactivated yeasts, spices, peas, malt extract, cocoa, and certain iron-rich leafy vegetables. Many seeds and nuts are good sources of zinc and it is advisable for vegetarians, especially, almond, peanut, cashew nut, brazil nut, pecans, pumpkin and squash seeds, sesame seeds, millet. These help prevent a deficiency of vitamin A, iron, and zinc. The contributed factors include the intake of calories, zinc, iron, methionine, lysine, arachidonic acid, calcium, and phosphorous. Increasing the intake of these nutrients during early childhood and through out the growth period may enhance the rate of growth and promote a larger body size.