Production of animal products requires more land and resources than plant-based foods, and now 75 percent of all agricultural land is used for animal production. The negative consequences of consuming more animal products affect the environment and future food availability, as well as world health. Greater animal product consumption is associated with increased risk for heart disease, diabetes, and cancer.
Source: http://pcrm.org/health/medNews/western-diet-unsustainable-for-planet