Rural America and poor urban enclaves. Here's a very short but seemingly well-cited article on the subject. Here's the obesity map of America. There are numerous studies indicating that obesity in America is nearing the top of the list as a leading cause of death. Here's a WaPo article on the matter.

I can't get behind the theory that the introduction of grains is the precise cause of the downfall of any society, including our own because there are many factors that lead to the downfall of health in societies. While obesity is a leading cause of death, there are many factors leading to it including economics, corporatism (desk jockey jobs, marketing of unhealthful products, long commutes, stress) as well as the sedentary nature of our society resulting from unsafe neighborhoods that keep kids inside, TV/Internet addictions, mental illness due to the disconnect from real-world social networks and over-consumption in its many forms that leads us to instant gratification.

While I think looking at our diets through an evolutionary lens is very important and helps us understand where we are today, we also need to address some of the factors that have happened just in the last 50 or 60 years in our very own society.

Check out this write-up by Dr. Eades on a study by Claire Cassidy:

http://www.proteinpower.com/drmike/low-carb-diets/nutrition-and-health-in-agriculturalists-and-hunter-gatherers/

Basically its about two groups of Pre-Columbian Native Americans, one hunter-gatherers and the others agriculturalists. Here is a quote from the study; "Overall, the agricultural Hardin Villagers were clearly less healthy than the Indian Knollers, who lived by hunting and gathering."

I work in Melanesia, where the rates of t-2 diabetes have sky rocketed in recent years due to the shift of diet from mainly seafood, root crops and pork to one based upon cheaply imported and ever widely distributed refined carbohydrates such as white rice and noodles as well as nasty HFCS products such as biscuits, corn snacks and other assorted sweets.

http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(10)61014-8/fulltext

"Population surveys in different islands have recorded rates of 47% in American Samoa; 44% in Tokelau; 32% in the Federated States of Micronesia (Pohnpei); 28% in the Marshall Islands and Kiribati; 23% in Nauru; and 14% in the Solomon Islands. As a comparison, in nearby Australia, the diabetes rate is 3·6%, whereas in 2007, the USA's overall population rate of diabetes was 7·8%."

The health related problem is severly testing the already under funded healthcare system, which lacks even the bare essentials, especially in rural areas. The problems have become widespread even in the few years I have been working in the Solomon Islands. Unfortunately, the Chinese have a total monopoly on the food import/distribution business, and this together with rising levels of cash economy (from subsistence based) have led many people to withdraw from traditional gardening and fishing practices and buy nutrient deficient calories from the Chinese merchants. The results are inevitable, and the short-term changes in health is staggering.

Just one example I know about, but this trend is widespread throughout the Pacific. Obesity, heart related diseases, diabetes etc all on the march.

Actually one of my hopes for this "Paleo" approach to health and well being, is that it can somehow move beyond the seemingly well educated North American following and into parts of the world where the questions about processed foodstuffs especially, are perhaps more pertinent to the entire health of a population, rather than talking about whether or not 3 cups of coffee is Paleo, or if one should feel guilty about the occasional taco. C'mon!.

Stature and robusticity during the agricultural transition: Evidence from the bioarchaeological record. Economics & Human Biology (2011)

You need access to the full-text to get the specific examples, but this study is recent and fairly comprehensive.

In Paleopathology at the Origins of Agriculture, this trend towards declining health was observed for 19 of 21 societies undergoing the agricultural transformation.agricultural transformation... The trend towards a decrease in adult height and a general reduction of overall health during times of subsistence change remains valid, with the majority of studies finding stature to decline as the reliance on agriculture increased. The impact of agriculture, accompanied by increasing population density and a rise in infectious disease, was observed to decrease stature in populations from across the entire globe and regardless of the temporal period during which agriculture was adopted, including Europe, Africa, the Middle East, Asia, South America, and North America.

This was specifically what Weston Price was studying in the early 1900's. He looked at pre-civilization populations and compared their rate of tooth decay (a proxy for overall health) to other cultures that were "modernized" and ate a western diet. He found that the primitive diet was much better for teeth and overall health.

The complete text of his book "Nutrition and Physical Degeneration" is available online, for example:

http://gutenberg.net.au/ebooks02/0200251h.html

An interesting quote:

"Since an important part of these studies involved a determination of the kinds and quantities of foods eaten, it was necessary to visit the sources available for purchasing foods in each town studied. In Stornoway, one could purchase angel food cake, white bread, as snow white as that to be found in any community in the world, many other white-flour products; also, canned marmalades, canned vegetables, sweetened fruit juices, jams, confections of every type filled the store windows and counters. These foods probably made a great appeal both because of their variety and their high sugar content to the pallets of these primitive people. The difference in physical appearance of the child life of Stornoway from that of the interior of the Isle of Lewis was striking. We found a family on the opposite coast of the island where the two boys shown in the upper half of Fig. 6 resided. One had excellent teeth and the other had rampant caries. These boys were brothers eating at the same table. The older boy, with excellent teeth, was still enjoying primitive food of oatmeal and oatcake and sea foods with some limited dairy products. The younger boy, seen to the left, had extensive tooth decay. Many teeth were missing including two in the front. He insisted on having white bread, jam, highly sweetened coffee and also sweet chocolates. His father told me with deep concern how difficult it was for this boy to get up in the morning and go to work."

This is the same Weston Price that is the basis of the Weston Price Foundation that promotes a "primitive" diet, similar to Paleo but with grains.