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Food production has a global link to the environment. As the world population increases, there are ever expanding demands on agriculture, but there are also increasing concerns about the impact of agriculture on the environment. Initial attempts to measure the impact of agriculture on the environment used a metric of greenhouse gas emissions/kcal of food produced to assess the relative impact of different foods and agriculture practices. This metric highlights the differential costs for production of grains versus livestock and led to conclusions that livestock have disproportionate negative impacts on the environment, leading many researchers and policy makers to call for a shift toward more plant-based diets. However, this metric implies that production of calories is the most important diet criterion and has been criticized for ignoring diet quality. One of the nutrients that must be considered in formulation of a sustainable diet is protein. Currently, livestock produces more than one-third of the world’s protein, and ruminant animals (ie, cattle, sheep and goats) have the unique capacity to convert nondigestible biomass (ie, grasses and forages) into high-quality protein. These factors highlight the need for prudent use of ruminants to optimize land use for production of adequate quantity and quality of protein. Any recommendations for changes in agriculture should consider impact on climate but must also focus on making optimal use of natural resources for creating healthy diets.