For thousands of years obesity was rarely seen. It was not until the 20th century that it became common — so much so that in 1997 the World Health Organization (WHO) formally recognized obesity as a global epidemic. In June of 2013 the American Medical Association classified obesity as a disease with much controversy. In 2014, a Lancet study estimated that the number of overweight adults in the world was 2.1 billion in 2013, compared with 857 million in 1980. The rate of obesity also increases with age at least up to 50 or 60 years old. Once considered a problem only of high-income countries, obesity rates are rising worldwide. These increases have been felt most dramatically in urban settings. The only remaining region of the world where obesity is not common is sub-Saharan Africa.