Knowledge in the role of plant-based diets on health had been shaped in part by cohort studies on vegetarians. We revisited publications from two ongoing longitudinal studies comprising large proportions of vegetarians-the Adventist Health Study-2 (AHS-2) and the European Prospective Investigation into Cancer and Nutrition-Oxford (EPIC-Oxford)-to describe the food and nutrient intake, health effects, and environmental sustainability outcomes of the dietary patterns identified in these studies. The vegetarian diet groups in both cohorts have essentially no meat intake, lower intake of fish and coffee, and higher intakes of vegetables and fruits compared to their non-vegetarian counterparts. In the AHS-2 cohort, vegetarians have higher intake of whole grains, legumes, nuts, and seeds. Vegans in AHS-2 have 16% reduced risk while vegans, vegetarians, and fish-eaters in EPIC-Oxford have 11-19% lower risk for all cancers compared to non-vegetarians. Pesco-vegetarians in the AHS-2 cohort had significantly lower mortality risk from all causes and ischemic heart disease while EPIC-Oxford fish-eaters had significantly lower all-cancers mortality risk than their non-vegetarians counterparts. Morbidity risks and prevalence rates for other chronic diseases were differentially reported in the two cohorts but vegetarians have lower risk than non-vegetarians. Greenhouse gas emissions of equicaloric diets are 29% less in vegetarian diet in AHS-2 and 47-60% less for vegetarian/vegan diets in EPIC-Oxford than non-vegetarian/meat-eating diets. The beneficial health outcomes and reduced carbon footprints make the case for adoption of vegetarian diets to address global food supply and environmental sustainability.