The Anthropocene crisis demands rapid, radical responses to reduce human consumption and impact on the environment in order to avert catastrophic effects on humans, other organisms, and the environment. The food system is a major contributor to this crisis and an essential component of an adequate response. Here we review current research to compare the environmental impacts of healthy, sustainable, plant-based diets (HSPBDs) v. standard omnivorous diets, and their potential for mitigating the negative environmental impacts of the food system. Because plant foods overall are much more ecologically efficient than animal-sourced foods (ASFs), many fewer resources are needed to produce them, and there are smaller environmental impacts—climate warming, nitrogen and phosphorus pollution, fresh-water use, air pollution, land use, and biodiversity loss—per unit mass, protein and calories of food. This means that HSPBDs also have much smaller impacts than standard omnivorous diets, and...