The united states has the highest rate of obesity in the world because of its population is obese.

The United States had the highest rate of obesity in the world, because ONE THIRD of its population is obese.
Obesity is a condition that is associated with having excess accumulated body fat, which can be deleterious to one's health. An individual is considered to be obese if the person's body weight is at least 20% more than it ought to be. Scientifically, obesity has been identified as the major cause of many chronic diseases such as diabetes mellitus, cardiovascular diseases, etc.