USA Is Fattest Nation Of 33 with developed economies, we're No. 1 By Nick McMaster, Newser Staff Posted Sep 23, 2010 5:08 PM CDT 39 comments Comments US waistlines are bulging. (Shutterstock) (Newser) – The US is ranked the fattest nation among those with developed economies in a new survey. With two-thirds of Americans either overweight or obese, the US tops the analysis by the Organization for Economic Cooperation and Development, USA Today reports. Mexico and Chile are the second and third fattest. But these countries shouldn't feel alone—obesity rates have exploded in most developed countries since the 1980s. (In terms of growth rates, the US again leads the way, followed by Australia and England.) Some notable exceptions are Japan, South Korea, and Switzerland, where only three in 10 people are overweight and one in 10 obese, says the report.