Imagine a biologist on an excursion in the Amazon looking for new plant species. He comes across a new grass he's never seen, and brings it back home to his lab in the U.S. He finds that the grass grows exceedingly well in greenhouses with the right fertilizer and soil, and he immediately moves to field trials. He also notices that the grass produces a seed that durable, storable, and extraordinarily calorie dense. The scientist immediately recognizes the potential for the newly discovered plant to solve global hunger problems and to meet the dietary demands of a growing world population.
But, there is a problem. Lab analysis reveals that the seeds are toxic to humans. Despite the set-back, the scientist doesn't give up. He toils away year after year until he creates a machine that can convert the seeds into a food that is not only safe for humans to eat but that is incredibly delicious to eat. There are a few downsides. For every five calories that go into the machine, only one comes out. Plus, the machine uses water, runs on electricity, burns fossil fuels, and creates CO2 emissions.
Should the scientist be condemned for his work? Or, hailed as an ingenious hero for finding a plant that can inexpensively produce calories, and then creating a machine that can turn those calories into something people really want to eat?
Maybe another way to think about it is to ask whether the scientist's new product can pass the market test; can his new food - despite it's inefficiencies (which will make the price higher than it otherwise would be) - compete against other foods in the marketplace? Recall, that the new food must be priced in a way that covers the cost of all the resources it uses - from the fertilizer to grow the new seeds to the gasoline required to run the new machine.
Now, let's call the new grass "corn" and the new machine "cow". The analogy isn't perfect (e.g., the cow is a living-feeling being and not a lifeless machine), but the thought experiment is useful nonetheless.
It's particularly useful in thinking about the argument that corn is "wasted" in the process of feeding animals. It is one that appears - in one form - in a recent paper in Science. West et al. write:
“Although crops used for animal feed ultimately produce human food in the form of meat and dairy products, they do so with a substantial loss of caloric efficiency. If current crop production used for animal feed and other nonfood uses (including biofuels) were targeted for direct consumption, ~70% more calories would become available, potentially providing enough calories to meet the basic needs of an additional 4 billion people (28). The human-edible crop calories that do not end up in the food system are referred to as the “diet gap.””
I'm not sure the logic of this sort of argument adds up.
Unlike my hypothetical example, corn is not toxic to humans (although some of the grasses cows eat really are inedible to humans). Nevertheless, few people really want to eat the calories that directly come from corn or other common animal feeds like soybeans.
So, why do we grow so much corn and soy? They are incredibly efficient producers of calories and protein. Stated differently, these crops (or "grasses" if you will) allow us to produce an inexpensive, bountiful supply of calories in a form that is storeable and easily transported.
The assumption in the quote of the Science article seems to either be that the "diet gap" will be solved by: 1) convincing people to eat the calories in corn and soy directly, or 2) that there are other tasty-edible crops that can be widely grown instead of corn and soy which can produce calories as efficiently as corn and soy. Aside from maybe rice or wheat (which also require some processing to become edible), the second assumption is almost certainly false. I'm also skeptical about the first assumption - that large swaths of people will voluntarily consume substantial calories directly from corn or soy.
What we typically do is take our relatively un-tasty corn and soy, and plug them into our machine (the cow or pig or chicken) to get a form of food we want to eat. Yes, it seems inefficient on the surface of it, but the key is to realize the that the original calories from corn and soy were not in a form most humans find desirable. As far as the human pallet is concerned, not all calories are created equal; we care a great deal about the form in which the calories are delivered to us.
The grass-machine analogy also helps make clear that it is probably a mistake to compare the calorie and CO2 footprint of the corn directly with the cow. I suspect only a very tiny fraction of the world's caloric consumption comes from directly consuming the raw corn or soy seeds. It takes energy to convert these seeds into an edible form – either through food processing or through animal feeding. So, what we want to compare is beef with other processed foods. Otherwise we're comparing apples and oranges (or in this case, corn and beef).