He always ate healthy-ish foods the past 10 years or so, he just had no portion control! His new diet is small portions with strict breaks in-between and he has even given some publicity to his nutritionist recently.
I don't think he's on drugs, he's also mentioned he's returned to Buddhism as well. He's been generally more positive/upbeat since he left prison. He's definitely undergone some change for the good, whether people like him or not.
I just wish he would stop that silly pout he makes on his tweet photos, it does his new thinner self no justice!