The statistics actually show problems beginning earlier than the dietary guidelines, but they certainly appear to have made the situation a lot worse. Dr. Michael Eades points this out, using photos taken from the Web.
Weston A. Price remarked that, as the populations he studied abandoned their traditional diets, the first sign was dental caries (cavities), then gout, then diabetes and hypertension, obesity, and cardiovascular disease. It’s not proof, of course, but there are statistics indicating that the number of new cases of Type II diabetes rises and falls with sugar consumption in the population, with about a 20-year lag.
I believe that cottonseed oil first began to be sold as a foodstuff in the early 19th century, and that industrial methods of refining sugar put cheap sugar on the market in the 1860’s. Our decline in health seems to have started at that point. Before cheap sugar and cheap refined flour flooded the market, gout and Type II diabetes were diseases found almost exclusively in the rich (Type I diabetes has been with us forever, since it is an autoimmune disease, not diet-related). Mike Eades’s lecture on “Palaeopathology and the Ketogenic Diet” is fascinating, because the Egyptians ate a diet very much like the one currently recommended, and they had all the same health problems we have.
Intriguingly, Gary Taubes cites a British colonial administration report from the mid-19th century, in which the Maasai, mostly animal eaters, were compared with their neighbors, the Kikuyu, who were mostly vegetarian. The Maasai were uniformly taller, stronger, and healthier, whereas the Kikuyu were shorter and had more health problems. Studies done in the 20th century that compared the Maasai who still retained the traditional diet with their relatives who had adopted the white man’s diet showed that the latter seemed to cause the same health problems in the Maasai that their colonial masters were experiencing.