Why is my cat so hungry?

He is regularly wormed - I have had him for 3 months and he is 11 months old and he has always wanted to eat soo much. I used to think it was psychological because he was homeless and underweight when the rehoming centre found him and I only fed him a little more than was recommended for his age and weight. Then he started getting into the bins and bread bin and tearing open loaves of bread and eating them so I have increased his food. He is meant to have three pouches of food but eats 4 and two bowls of biscuits - he is still a healthy weight after a couple of months of this (I can just see his ribs) so do not think he can be overeating? He's not particularly overactive.