If someone has already trademarked a word in a food category for a tea under class ic 005 and ic 030 can I trademark that word in dietary supplements?

There is a small chance you could but a morely outcome is that you cannot. Further, even if you made it by a technicality or by an error, you would never develop the same goodwill in your product as if you used a torally original name. Further, even with trademark registration, there might still exist claims under state law for unfair competition and other legal theories.