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Methodology and Resources

Greenhouse Gas Emissions 
The statistics on greenhouse gas emissions were derived from numbers in “Diet, Energy, and Global Warming,” by Gidon Eshel and Pamela A. Martin of the University of Chicago. It was published in Earth Interactions, volume 10 in 2006. The authors calculated the greenhouse gas emissions produced by various diets and compared the environmental benefits to driving hybrid versus standard cars. We figured out the daily greenhouse gas outputs from the authors' yearly figures on animal-product-based and animal-product-free diets and then assumed that the average lunch would be about 28% of the daily figures. The authors also calculated the average yearly CO2 output for the Toyota Prius and Camry, which we broke down to daily figures to complete the picture.

The water statistics were derived from cubic meters per ton figures in the appendices of a 2004 UNESCO Institute for Water Education report called the Water Footprints of Nations, available at We looked at recipes and then online at restaurant menu information to figure out the weight of the relevant ingredients, for example about 3oz of beef for a typical hamburger or about two and a half ounces of dry beans per serving of black bean soup, from which it was pretty simple to get the difference in gallons of water used per serving.

The land statistics were derived from numbers on land use (that animal products take 6 to 17 times as much land as soy to produce the same amount of protein) in “Quantification of the environmental impact of different dietary protein choices” by Lucas Reijnders and Sam Soret, which appeared in a 2003 supplement to the American Journal of Clinical Nutrition and on the protein output per acre for soy and for peanuts reported in the 1996 edition of Food, Energy, and Society edited by Pimentel and Pimentel. We used these numbers to figure out the square feet per serving and then compare animal-product foods to animal-product-free foods.

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We're happy to share more information on how we got to our numbers beyond what we've posted on the website. If you have questions about our methods and calculations, please don't hesitate to email us. 
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