First of all what is Obesity?
A person falls under the Obese bracket, if his BMI is more than 32Kg/square meter. Another simpler way to determine whether a person is obese is explained here.
Following the above standards, the top five most obese countries in the world are (from most obese to the least | Data: Organisation for Economic Co-operation and Development ):
3) New Zealand
According to the data, Obesity rates vary widely across globe, from a low of 4% in Japan and Korea, to 30% or more in the United States and Mexico.
The main reasons responsible for Obesity endemic many developed countries are:
Sedentary lifestyle, more intake of fast foods and little or no exercise. Fast Foods with bad calories are also to blame.