Audrey is right, dry food is the worst possible diet for a cat.
I also used to feed a lot of dried food to my cats and none of them were more than slightly overweight, but now I've researched the subject thoroughly, I have realised that dry food could be damaging my cats' health so as of last week they have not had one single biscuit!

Check out Dr Elizabeth Hodgkin's recent book "Your Cat"
All About Cats Health and Wellness Center - Your Cat

If anyone can read that and continue feeding dried food, I'll be very surprised