Cat has light, runny, SMELLY poop

[ronny_cat]

My 10 month old cat often meows loudly for a good minute or two before he has to go poop. When this happens, the poop is runny and light brown, and the smell is terrible... it fills our apartment. Other than this he is a very happy and active cat who has no problems eating. I feel so bad for him and I am wondering if he should see a vet? We feed him IAMs both dry and wet food and have not recently changed his diet or anything.

Thanks!