Mark Eisler and co-authors advocate eating only 300 grams of red meat a week (roughly the volume of three decks of playing cards) as a step towards producing sustainable livestock (Nature 507, 32–34; 2014). That amount corresponds to 3.5–7% of a 2,000-calorie-a-day diet, depending on the cut and type of meat. Such a move would also make for a more equitable global distribution of animal-product consumption; these products comprise around 48% of the average diet in the United States, for example (S. Bonhommeau et al. Proc. Natl Acad. Sci. USA 110, 20617–20620; 2013).

Imposing a global dietary limit of 5% red meat as part of a 10% maximum for all animal-based products would enable more people to be fed using less land. For example, eliminating livestock and using existing agricultural lands to grow crops for direct human consumption instead of for livestock fodder could feed an extra 4 billion people (E. S. Cassidy et al. Environ. Res. Lett. 8, 034015; 2013), thereby reducing or eliminating the greenhouse-gas emissions and biodiversity loss associated with conversion of natural habitats. This would also reduce many other environmental impacts of agriculture that relate to the use of water, fertilizer and fossil fuels.