Causes of obesity
Obesity is usually the cause of some one eating more in terms of calories, than their body needs, or can process. The problem is exacerbated by the over consumption of foods high in fats and in sugars.
This can be set off to some extent by the body burning off the excess calories from food over-consumed and not needed by the body. If the body can't use the calories, then the energy is changed to deposits of fat. These are found throughout the body, but particularly in the torso, and around the waist.
Modern living, especially in the west, usually means over-eating. Most people in western civilisations now consume excessive amounts of very high calorie-rich food.
We also tend to lead increasingly sedentary lives, sat at desks or in vehicles travelling, whereas previously people did more hard physically demanding work. We also tend to use transport more than we used to; previously we would walk almost everywhere but now we ride around in cars, buses or trains to travel everywhere.
Children too spend increasingly higher amounts of time sat infront of TV and other screens instead of getting exercise they would otherwise benefit from while outside playing.
While sat around and not moving much, the metabolism slows down, and the body loses its ability to regulate blood sugar and the blood pressure. This results in the body not burning off so much of the energy, which remains as fat in the body.
You can read here
why sitting down so much is very bad for our bodies (link to NHS web site).
There are some health conditions which may make some people obese. These include such conditions as hypothyroidism (which is basically an underactive thyroid gland), but these ailments won't cause obesity if they are properly treated with medication. This means there is absolutely no excuse or reason for anyone to be obese.