Obesity is defined as a great accumulation of fats that can be damaging to health. It is a big global problem, with estimates that by 2015 there will be over 2.3 billion adults who are overweight or obese. The main causes of obesity are nutritional disorders due to a worldwide change in diet to foods high in calories but low in vitamins and minerals, as well as a tendency toward reduced physical activity. Countries with high rates of obesity include North America and Australia.