Our knowledge is far from complete regarding the relationship between vegetarian diets and human health. However, scientific advances in the last decades have considerably changed the role that vegetarian diets may play in human nutrition. Components of a healthy vegetarian diet include a variety of vegetables, fruits, whole grain cereals, legumes and nuts. Numerous studies show important and quantifiable benefits of the different components of vegetarian diets, namely the reduction of risk for many chronic diseases and the increase in longevity. Such evidence is derived from the study of vegetarians as well as other populations. While meat intake has been related to increased risk for a variety of chronic diseases, an abundant consumption of vegetables, fruits, cereals, nuts, and legumes all have been independently related with a lower risk for several chronic degenerative diseases, such as ischemic heart disease, diabetes, obesity, and many cancers. Hence, whole foods of plant origin seem to be beneficial on their own merit for chronic disease prevention. This is possibly more certain than the detrimental effects of meats. Vegetarian diets, as any other diet pattern, have potential health risks, namely marginal intake of essential nutrients. However, from the public health viewpoint the health benefits of a well-planned vegetarian diet far outweigh the potential risks.