Noah was 6.5kg (a stone
) at his February weigh-in, which the vet was happy with but I know he can't wash his bum and has no waist. If my scales are correct he has lost 0.5kg over the summer just by stopping dry and only having raw or a good commercial wet. I can't take the credit as it happened by accident, given that he is a complete piglet that is a result!
Another vote for cutting back on any dry that contains grains, as others said they contribute to weight gain in dogs and cats. Watch the 'Light' foods, some are lower in fat which reduces the calorie content, others replace meat with cereals (Hills) which is nonsensical as they both supply 4 calories a gram. It's actually not that senseless as fibre can help to fill the tummy and floor sweepings from cereal mills are cheap as chips.
You could try supplementing their wet food with a little water and ground flax seeds or Protexin from VetUK - both of which supply filling soluble fibre.
Mark for that tip ages ago!