It seems impossible?
They eat 2 pouches a day of Felix (each) and I always have dry food down too, like the Purina stuff.
They both love their food and badger constantly for stuff, they have the occasional Dreamie too. They're not hugely active and mostly house cats (their choice, they're just not bothered about going outside).
I've said to DH we should take away the dry stuff as they are 9 and 7 now, they're getting middle age spread but he says I'm starving them! My MIL is the same, says they're 'skinny' but they're not, just not grossly obese like her two.
I read an article that said fat dogs have fat owners but it's not the same for cats, all of us are not overweight but our cats are!