Advocates of a plant-based diet tout a wide variety of benefits: they say it’s more nutritious; that it reduces the chances of food-borne illnesses like E. coli; that it is better across all sorts of environmental metrics like land use, energy use, water use, greenhouse gas emissions, and local pollution; that it is better for animal welfare; that it is better for agricultural workers; and that it  is more economically efficient, which means it need fewer government subsidies and fewer natural resources spent on the same amount of nutrients and calories. The latest example is Matthew Prescott’s Food Is the Solution: What to Eat to Save the World. Prescott works at The Humane Society of the United States, America’s largest animal charity. Within the first few pages, a brief foreword by Hollywood director James Cameron argues for the environmental benefits of a plant-based diet, then Prescott’s introduction claims that plant-based food can “prevent and reverse” heart disease, diabetes, cancer, stroke, obesity, and autoimmune disorders. But given the many possible human diets from paleo to DASH, isn’t …