Vegetarian dietary patterns are rather diverse due to the wide range of available food choices and the different motivational factors of adopting such patterns. The potential health outcomes of vegetarian diets have been extensively investigated, with the majority of studies indicating favorable effects against cardiometabolic risk factors and lower risk of major chronic diseases. Nevertheless, there are health concerns regarding the adequacy of several nutrients, i.e. vitamin B12, vitamin D, ω-3 fatty acids, calcium, iron, and zinc. Vegetarian diets are negatively associated with bone mass density and skeletal muscle mass especially in older people, while vegetarians are at high risk for iron deficiency. The Dietary Reference Intakes report, suggests that vegetarians should consume 1.8 times more iron than the RDA, while vegetarian iron sources are less bioavailable. Dietary protein may represent similar considerations, while protein quality and digestibility are recognized as potential concerns also influencing gut microbiota. Specific population groups i.e. pregnant women, children, elderly and athletes may run the risk of malnutrition. A negative impact on cognitive and mental health has been reported too. When a vegetarian diet is appropriately planned and includes fortified foods and/or supplements, it can be nutritionally adequate for adults and children and can promote health.