Although their anatomical features disclose the herbivorous nature of humans, an omnivorous diet can be considered an evolutionary advantage that has supported human survival. Over recent decades, vegetarianism has significantly increased in developed countries due to the support of scientific research, emerging supermarkets and restaurants, and easy-to-access soy products and healthy foods. According to current knowledge, vegetarian diets are associated with significantly lower prevalence of obesity and lower risk of cardiovascular mortality. However, while the overall risk of cancer is slightly lower in vegetarians, the findings regarding the location and type of cancer that can be prevented by vegetarian diets are inconclusive. In addition to this, it remains unclear whether health benefits of vegetarian diets can be attributed to the avoidance of meat, or to the increased intake of dietary fibre, n-6 fatty acids, vitamins C, B9 and E, potassium, magnesium and phyto-chemicals, or to both of these factors. As a vegetarian diet becomes more restrictive, intake of adequate daily energy and of n-3 fatty acids, essential amino acids, vitamin B12, zinc, calcium and iron becomes more difficult to achieve, which is particularly challenging in children who have higher nutrient requirements relative to body weight than adults.