I think that forbidding something makes the tendency to abuse it worse....just look at the drinking age here vs Germany and the issues we have here compared to Germany.
Once you run out of sweets then he will have to wait for more. I suggest buying what you feel comfortable with ...understanding that you probably won't get to eat much of it, but buy smaller amounts so that they are consumed quickly by him. Then if he wants more, he might have to just get a job.
You can also let him see something of what might await him. There was a tv special on
morbid obesity that might inspire him to think of a few unattractive futures.