A. Claire Cheng, a dietetic intern at the Tufts University Frances Stern Nutrition Center answers: “A vegan diet can be nutritious, environmentally friendly, and consistent with overall good health. Vegans do not consume any animal products, including eggs or dairy (and even honey). There are some key nutrients of concern for under-consumption for those following a vegan diet, including vitamin B12, iron, calcium, and vitamin D.
Vitamin B12 is naturally found only in animal products. The Academy of Nutrition and Dietetics recommends people following a vegan diet consume fortified foods, otherwise vitamin B12 supplements may be necessary. (Fermented foods and unfortified nutritional yeast are not considered adequate sources of this vitamin.)
Iron from plant sources is not as well absorbed as iron from animal foods. It is important to consume plenty of plant foods that are high in iron, such as legumes (lentils and beans), tofu, nuts and seeds, dried fruit, and fortified breakfast cereal. Eating iron-rich foods along with vitamin C rich foods (like strawberries, oranges, and peppers) facilitates iron absorption. Some sources recommend vegans and vegetarians aim for more dietary iron intake than the recommended eight milligrams (mg) per day for females over 51 and adult males or 18 mg per day for females 19 to 50.
Calcium is found in many plant foods, especially dark leafy greens, but is not well absorbed due to the presence of compounds called oxalates and phytates that bind with the calcium. Kale, turnip greens, and bok choy (low-oxalate greens) are better calcium sources than spinach, beet greens, and Swiss chard (high-oxalate greens). Calcium from foods such as fortified plant “milks” or juices and tofu set with calcium salts is generally well-absorbed. Aim for 1,000 to 1,200 milligrams of calcium a day. Vitamin D is critical to calcium absorption. Adequate sunlight exposure and fortified foods are the best ways to keep vitamin D levels up.
“When adopting a vegan diet in the long term, there are three important things to keep in mind. First, foods are a better source of nutrients compared to supplements. Only vitamin B12 may need to be obtained from outside sources. Second, be careful with the definition of a ‘plant-based’ diet. An ideal plant-based diet should include plenty of legumes, nuts/seeds, fruits and vegetables, and whole grains. A diet high in refined grains such as pasta and fried potatoes is plant-based, but unhealthy. Lastly, always consult your physician or a dietitian if you are going to adopt a vegan diet.”