Lupin was like this when I first got him but abs didnt work at all and they also destroy the good bacteria.........tried chicken, fish.....the latter made him ill immediately!
The vet gave me probiotic capsules cos they build up the good bacteria......think protexin but cant remember and he was put on Royal canin gastro intestinal pouches, bought online as cheaper than vets but still expensive and this cured him.
Then problem was what cat food and the silliest one became his stable for months...........Tesco chicken in jelly pouches!!
He gets fed up with the same food and moved to sheba chicken something which they bloomin stopped making and then tried felix jelly pouches and his stable now is the fish ones!! But will not give him fresh boiled fish cos too scared.