Actually, Bettas are smarter than you give them credit for. My fat betta generally learns from his constipation; much like a cat or rat. He might eat something once or twice, but if it makes him bloated, he'll stop. My betta got a little bloated; now he doesn't engulf everything like he used too. My betta even lets worms float for a min or so before attacking them. My betta also looks a lot better now (no longer bloated). I think because the pellets were new, the betta tried them. He isn't nearly as fat looking. It only took 3 days and light feedings of the tank.