It was a doctor's observation. While operating on Afghan soldiers who have limited access to processed foods and a western lifestyle the fat deposits were not found as abundantly internally.
It serves as a launching point to describe the point of the article and book.
Your premise and statistics are a bit on the hand-waving side, of course no one is calling Afghanistan and Pakistan models of health.
And life expectancy is not a proper measure of health either, as per capita (~2006) Afghan people had $29 as the total expenditure on health per capita. The United States? $6,714. We may live longer but we have a lot more help in getting there.