Before you do anything, try not to make a big deal of your son's issue.
Teenagers are self conscious enough and you do not want him to feel worse than he probably already does.
All those hormones raging around are difficult enough to deal with never mind overanxious parents.
I am not suggesting you ignore the problem, quite the opposite.
Just don't tell him that he needs to lose lots of weight.
The first thing you need to do is take your son for a full medical checkup.
This is to ensure that there is no underlying condition causing his weight gain.
Also if he is obese, you should follow your doctor's advice with regard to suitable activities as well as a recommended calorie intake and suitable weight loss program.
Eating is a pleasant activity and food is there to be enjoyed and this is the attitude we need to adopt in our homes.
As soon as you start banning particular items, you are almost guaranteed that your child will want them.
Instead, we need to re-educate them gently into the ways of healthy eating.
Mention the word diet and you will probably have a rebellion on your hands.
So don't mention low calorie or low fat, but just gradually swap the obvious items.
For example if they like cottage cheese, get the one made with skimmed milk and use low fat mayonnaise.
You can reduce your child's calorie intake subtly so that they may not even notice.
For example, try slightly reducing the size of their meals.
If they love pizza or curry, make your own at home.
You can reduce the fat and salt content thereby helping them to lose pounds.
Encourage them to eat more fruit and vegetables.
OK so that last one may not be easy but there are ways around everything.
Think of how you used to mask vegetables when they were toddlers i.
e.
in soups, blended into tomato sauces etc.