A vegan diet is characterized by abstinence from all animal-sourced products.  It differs from a vegetarian diet in that vegetarians consume some nonmeat animal products (eg, milk, eggs).  A vegan diet is plentiful in most vitamins (eg, A, B complex [except B₁₂], C), minerals (eg, potassium, magnesium), and soluble fiber.  In addition, although most single plant–based protein sources (except soy) are deficient in certain essential amino acids, dietary requirements can be met with a mixed vegan diet (eg, legumes plus grains).

However, a vegan diet without supplementation or food fortification (as in this case) increases the risk for the following:

• Vitamin B₁₂ (cobalamin) deficiency:  Vitamin B₁₂ is naturally present in only animal-based foods.  Deficiency usually takes years to develop after initiating a strict vegan diet due to large hepatic stores of vitamin B₁₂.

• Calcium and vitamin D deficiency:  Most dietary calcium and vitamin D intake is from animal-sourced products (eg, dairy).  Individuals who follow a vegan diet often require supplementation to prevent osteoporosis, especially those without significant sunlight exposure (sunlight accounts for ~200-400 IU/day of the required 600 IU/day).

• Iron deficiency:  Many plant products (eg, leafy green vegetables) contain iron.  However, the iron derived from plants (nonheme iron) is less well absorbed compared with iron derived from animals (heme iron).  In addition, the quantity is often inadequate for those with increased dietary iron requirements, such as children during periods of rapid growth and women who are menstruating (like this young woman) (Choice A).

This patient developed fatigue and malaise after 5 years of following a strict vegan diet.  Although many commercially prepared vegan products are fortified with additional vitamins and minerals, this patient is consuming unprocessed whole foods only.  She likely has anemia due to iron and/or vitamin B₁₂ deficiency.

(Choices B, D, E, and F)  Folic acid and thiamine (vitamin B₁) are abundant in plant-based foods.  Deficiency may occur in individuals with poor absorption (eg, alcohol use disorder) or malnutrition but is uncommon in those consuming a variety of fruits, vegetables, and grains.

Educational objective:
A vegan diet is characterized by abstinence from all animal-sourced products.  Individuals who consume a vegan diet are often deficient in vitamin B₁₂, calcium, and vitamin D.  Those with increased dietary iron requirements (eg, menstruating women, children) may also develop iron deficiency.  Supplementation is routinely recommended.