The New York Times health columnist Jane Brody perfectly encapsulated this idea when she wrote, “Within this century, the diet of the average American has undergone a radical shift away from plant-based foods such as grains, beans and peas, nuts, potatoes, and other vegetables and fruits and toward foods derived from animals—meat, fish, poultry, eggs and dairy products.” It is a view that has been echoed in literally hundreds of official reports.

The justification for this idea, that our ancestors lived mainly on fruits, vegetables, and grains, comes mainly from the USDA “food disappearance data.” The “disappearance” of food is an approximation of supply; most of it is probably being eaten, but much is wasted, too. Experts therefore acknowledge that the disappearance numbers are merely rough estimates of consumption. The data from the early 1900s, which is what Brody, McGovern, and others used, are known to be especially poor. Among other things, these data accounted only for the meat, dairy, and other fresh foods shipped across state lines in those early years, so anything produced and eaten locally, such as meat from a cow or eggs from chickens, would not have been included. And since farmers made up more than a quarter of all workers during these years, local foods must have amounted to quite a lot. Experts agree that this early availability data are not adequate for serious use, yet they cite the numbers anyway, because no other data are available. And for the years before 1900, there are no “scientific” data at all.