Michael Pollan argues in In Defense of Food that our diets are less diverse than they once were. He explains,
Today [corn, soy, wheat, and rice] account for two thirds of the calories we eat. When you consider that humankind has historically consumed some eighty thousand edible species, and that three thousand of these have been in widespread use, this represents a radical simplification of the human diet. (117)
This is a rather egregious abuse of the numbers. Yes, three thousand species is many more than four species, but these numbers are measuring very different things.
I’ll start with the smallest problem. As Pollan notes, much of the corn and soy is actually fed to animals to produce meats and other animal products for human consumption. Yet for some reason, he doesn’t bother to include the animal species in his count here.
A bigger issue is that when he refers to the number of species that have been historically eaten, he seems to be including species that have been eaten by various cultures across different time periods. This means, for instance, that it includes both the American bison eaten by the Native Americans of the Great Plains and the cassava that has long been a staple in South America. Of course, geographical considerations dictate that it’s highly unlikely that many people have regularly eaten both of these species, so the “eighty thousand edible species” is misleading because it tells us nothing about what any particular group of people have historically eaten.
It’s also deeply misleading to use the four species that provide most of our calories as an indicator of the diversity of our diet. The fact is that some edible species don’t have many calories. If you wanted to get more than a third of your calories from the leafy vegetables that Pollan argues we should be eating more of, you’d better be prepared to wolf down more than three pounds of greens per day. And we could easily add a few dozen species to the list just by visiting the spice aisle of a grocery store, even if there are very few calories to be found there.
So is the American diet unusually homogeneous? I don’t have the time or resources to make that determination, but the evidence certainly isn’t in the data that Pollan cites. However, there is evidence that we are not alone in our dependence on a small number of crops. For example, the United Nations Food and Agriculture Organization estimated that about thirty years ago rice alone contributed 68% of calories to South Asian diets.