Archive for June, 2005
I’m reading pieces of the book “Feeding the World” by Vaclav Smil. Among other things, he compares the energy efficiencies of diary, eggs, and various meats and discusses potential improvements in production.
One of the most powerful points he makes is that, from the perspective of energy-efficiency, or land-efficiency, or maximizing the earth’s carrying capacity, there’s an optimal level of meat consumption that is probably less than the American per-capita average, but definitely nonzero.
The usual argument is that it takes 10 pounds of grain to produce a pound of beef, so we can feed more people by not raising beef. But not all livestock is grain fed. In particular, a lot of livestock grazes on pasture land, agricultural residues, and legumes planted in rotation with food species; these are not in competition with human food crops. Sea animals generally do not compete with human food crops either. The implication is that the best-managed food supply would involve some meat production, even if you use all the land possible for human crops.
One might extend this to decide that it’s (environmentally) ethical to have a diet that includes a small amount of meat. Smil also gives some evolutionary arguments for why eating some meat (say, a tenth of that in the American diet) is biologically adaptive for humans.
If one decides that some meat should be consumed, then there are more and less efficient animals to eat, and Smil presents a lot of quantitative data on this. On every measure, beef comes out the worst (e.g. 5-8% protein conversion efficiency). Eggs (30-40%), and particularly milk (30-40%), and salmon (40-45%) come out pretty good on conversion efficiency. Eggs and milk also do well on land use, chickens and eggs on water use. Pigs look good a number of measures, partly because they eat a lot of agricultural waste and they digest it efficiently, but I actually think Smil gets it wrong on the benefits of pigs because he’s ignoring the life cycle issues with hog waste (nasty water pollution).
Overall, I’d say there’s strong support for lactoovo vegetarianism. There’s also good support for eating, say, fish but not other meat, or poultry but not beef, from an energy-balance perspective. This is also a conclusion I drew from the life-cycle analyses of meats in The Consumer’s Guide to Effective Environmental Choices..