Anecdotely the stoners I know do eat shitty food. I believe their exists a blackhole that's hard to get out of. You feel shitty or stressed, smoke, eat shitty food because motivation is gone to do other things, feel shitty the next day because your body is surviving on garbage calories, repeat.

I had a family member that needed mental health care, first thing they did was alter the diet and check vitimin levels, because its hard to get mentally well if you aren't physically well.