Eshel’s team analysed how much land, water and nitrogen fertiliser was needed to raise beef and compared this with poultry, pork, eggs and dairy produce. Beef had a far greater impact than all the others because as ruminants, cattle make far less efficient use of their feed. “Only a minute fraction of the food consumed by cattle goes into the bloodstream, so the bulk of the energy is lost,” said Eshel. Feeding cattle on grain rather than grass exacerbates this inefficiency, although Eshel noted that even grass-fed cattle still have greater environmental footprints than other animal produce. The footprint of lamb, relatively rarely eaten in the US, was not considered in the study published in the journal Proceedings of the National Academy of Sciences.