You could say something along the lines of:
"Hey, Friend, what's so good about weed? Why are you always smoking it?"
If he's smoking it for medical purposes, then just drop it, but if it's illegal and he's doing it to "look cool", then I would further ask questions about it.
Foods that have more calories, typically have more carbs. To simplify things, carbs make people feel better.
Answer:
Fiber slows the rate that sugar is absorbed into the bloodstream which makes it less likely to get diabetes. It has benefits for a heart to be healthy.
