BACKGROUND:Beneficial effects of vegetarian and vegan diets on health outcomes have been supposed in previous studies. OBJECTIVES:Aim of this study was to clarify the association between vegetarian, vegan diets, risk factors for chronic diseases, risk of all-cause mortality, incidence and mortality from cardio-cerebrovascular diseases, total cancer and specific type of cancer (colorectal, breast, prostate and lung), through meta-analysis. METHODS:A comprehensive search of Medline, EMBASE, Scopus, The Cochrane Library and Google Scholar was conducted.