Still think it's a more broken version of Toki's fruit tbh: just being able to stop time. That's why he doesn't have to eat, he freezes time on his stomach.
It also sort of fits the potential new "universal constants" theme going on between the 3 admirals: Light, Gravity and Time.
Then again, it could also be a Logia, Paramecia and Zoan combo so there's that too. If it's Zoan, I wonder what characteristic allows him to not eat for 3 years.
Edit: ohhhh maybe it's a mythical zoan that can stop time!