Abit of background:

My cats have been on Innova lite cat dry food for approx 1.5 years and
they've had no problems with it at all. A few weeks ago, I started a new
bag of Innova and they started having diarrhea and vomiting. I switched
over to Science Diet ID to clear up the diarrhea. I reintroduced Innova
(same bag) back into their diet and the diarrhea resumed. After putting
the cats back on ID for awhile, I started the cats on another bag on
Innova (same expiration date as the prior) and the diarrhea resume. After
putting the cats back on strictly ID, I then started them on another bag
on Innova with a different expiration date but the diarrhea came back.
I switched them back onto ID and I reintroduced Innova canned food (they
were previously on the canned food but I didn't feed them any can food
since the start of the diarrhea), for awhile it seemed fine but now
they're experiencing diarrhea and vomiting again.

I've experimented with bags of Innova with 4 different sets of expiration
dates and the result has been quite consistent. I am switching them to
another diet - experimenting with Wellness and Burn's.

Now the question, it looks as if they've suddenly developed an intolerance
to Innova - I phoned up Natura and they haven't changed any of their
formula so it would seem that something else is happening. Some person at
my pet food store suggested that with gourmet cat foods, sometimes it's
too rich for them. Is this valid? What else might be happening?

My cats are strictly indoors and nothing else changed in their
environment, etc. They were formerly free-fed but I have since switched
them to fixed feeding but that was sometime during the fight with diarrhea
and is unlikely to be responsible.

Thanks.
Amy