One of cats, Mini, has always been skinny to the point of being boney. Even feeding her kitten food did not help. She has never shown much interest in any food.
Changing to Orijen dried (from Science plan) changed that. She really likes it and is putting on some weight for the first time in her life (she is 9). It is down all the time (and no, none of the cats are overweight).
I also give them an evening treat of Applaws, one 156g can between four, and Mini actually squeaks to be given her share! Strangely enough, she wasn't that keen on chicken breast or tuna before I started feeding the Orijen. Maybe her digestive system is just working better.
Also, she is producing many fewer hairballs.
Changing to a non-grain food was a really good idea for all mine but for Mini in particular. Mark, I wonder about trying Willow on a grain-free diet?
Also, although Orijen looks expensive they never waste any and they eat less of it.