Vegan and vegetarian diets are lauded by the conventional medical and nutrition establishments for their purported health benefits. In fact, the American Dietetic Association has even stated that vegan and vegetarian diets are “appropriate during all life cycle stages, including pregnancy, lactation, infancy, childhood, and adolescence.” (1) As someone with a deep background in nutritional biochemistry and human physiology, this broad statement gives me pause – where is the evidence indicating that vegan and vegetarian diets are safe and optimal for all life stages? Given that the medical and nutrition establishments have previously been quite wrong about some important topics, such as the [lack of] relationship between saturated fat and heart disease, I hesitate to endorse their position on the safety of plant-based diets for all life stages. In this blog series, my goal is to demonstrate that vegan and vegetarian diets are not optimal for all life stages and that in some life stages, they may actually be harmful.