Vegetarian and vegan diets are becoming increasingly popular as people become more aware of the benefits they offer to human health and the environment. Even though vegetarian diets have been associated with a decreased risk of death and chronic illnesses, followers of these diets might not acquire adequate nutrients, which could limit the benefits to their health. The main nutrients to be concerned about are iron, calcium, vitamin B12, vitamin D, iodine, and selenium. Anyone following a vegetarian or vegan diet needs to take vitamin B12 supplements. To avoid vitamin B12 deficiency, adults should take 50 μg - 100 μg of cyanocobalamin orally once a day or twice a week at 2000 μg. Iodine supplements are recommended for pregnant and lactating women, as well as vegetarians and vegans who are unable to consume sea vegetables or iodine-fortified foods. Adults should take 150 μg of iodine supplements every day. Understanding the entire spectrum of effects of a vegetarian diet - not just the nutritional ones-is essential. In addition to providing more reliable data, studies in this area may assist in eliminating all factors that could deter people from adopting a vegetarian diet or negatively impact the quality of life of those who already do so.