After several decades of constant growth in the past decade obesity did not grow any more among children [1] and adults [2]. Some authors would claim banning vending machines from schools and other such restrictive measures responsible [3].
I think that obesity is a polygenetic disorder, the alleles that determine the phenotype have a certain prevalence in our population. For centuries these alleles have been being kept in check by insufficient food supply. Now with a population's growing wealth there was no more external obesity control and slowly but unremittingly the phenotype of a population developed according its genotype. I'm convinced the prevalence of obesity alleles is not 100%, so we would never by any measures end up with a population of 100% obese people. On the contrary, I guess the prevalence of obesity genes is about 25% that is reached about now, so I doubt that banning vending machines from school had any measurable effect.
References
1. Cynthia L Ogden u. a., „Prevalence of Obesity and Trends in Body Mass Index Among US Children and Adolescents, 1999-2010“, JAMA: The Journal of the American Medical Association (Januar 17, 2012), http://www.ncbi.nlm.nih.gov/pubmed/22253364.
2. Katherine M Flegal u. a., „Prevalence of Obesity and Trends in the Distribution of Body Mass Index Among US Adults, 1999-2010“, JAMA: The Journal of the American Medical Association (Januar 20, 2012), http://www.ncbi.nlm.nih.gov/pubmed/22253363.
3. Sarah Kliff, „Why are obesity rates leveling off?“, The Washington Post - Blogs, Januar 18, 2012, http://www.washingtonpost.com/blogs/ezra-klein/post/why-are-obesity-rates-leveling-off/2012/01/17/gIQAT0GF6P_blog.html.
