Jayson Lusk points to the following 2013 Environmental Letters paper:
Redefining agricultural yields: from tonnes to people nourished per hectare
Emily S Cassidy, Paul C West, James S Gerber and Jonathan A Foley
Published 1 August 2013 2013
Environmental Research Letters, Volume 8, Number 3
He has a lot of interesting things to say about this work. He uses this analogy:
"there are two ways to view livestock. One is that they are inefficient - using up a lot of energy to make food. Another is that they are good at converting one form of energy that is highly storeable/transportable but untasty (field corn, soy, sorghum) to another form (eggs, meat, dairy) that we like to eat. Rarely do these sorts of research papers include the the calories (or energy) used in food processing. It is a mistake to compare the calories in steak to the calories in a wheat kernel. The wheat kernel requires energy/processing to convert to flour and then more energy to get pasta or bread."
He also links to this report from the Council for Science and Technology that does a deep dive looking at this conversion in livestock production.
I also like the way 'efficiency' is stated in Heyne, Boettke, and Prychitco's The Economic Way of Thinking text.
"efficiency is essentially an evaluative term. It always has to do with the ratio fo the value of output to the value of input" in effect it depends on what people want done and how they value what they want done. "It follows that the efficiency of any process can change with changes in valuations."
What I am getting at is that maybe people prefer to have sustenance from beef vs rice and we have to give weight to that in a policy framework. Physical and technical facts alone can never fully determine efficiency. That's what makes economics so powerful. Its the study of people's choices and how they are made compatible. It is way more than just the study of the technical allocation of resources because it forces us to consider each individual's preferences based on the knowledge of their specific circumstances of time and place.