A sedentary lifestyle and too many high fat foods are undisputably the major causes of obesity. If your calorific intake is higher than you burn off then the excess turns to body fat.

Note I said major cause. I believe less than 10% of obesity has been put down to medical reasons.

If he bloated up due to a medical condition then it would be beyond his control. If he was in the other 90% he would have to ask Jamie Oliver around for dinner and take note of the advice he dishes out. (Preferably small dishes.)