yup, diet plays a major role - excessive gas is a clear sign that something isn't quite functioning the way it should be.
often you can help things along quite well with a good quality probiotic supplement. innova has some probiotics added already, but sometimes that's not quite enough.
there are many different probiotic products on the market, some made especially for pets, but most of those aren't of particularly high quality.
personally i use NOW brand 4x6 acidophilus powder. it's easier to dose than tablets and it has a pleasant taste, much like powdered milk. 1/4 teaspoon per day, possibly divided up into 2 feedings, should do the trick. for cats half the dose is sufficient.
probiotics don't only support and protect the digestive tract, but also the immune system.