Have you wormed him? If he is eating that much and is literally skin and bones, makes me wonder.

As for food, I have fed Diamond, but I do not like the dog's coat on it, however it is a quality food, but there are better ones out there. Pedigree is junk and should be avoided. If you feed Diamond, I suggest you buy the Kirkland brand at Costco -- it the green bag Diamond food and runs about $15 per bag.

Lots of guys with multiple dogs feed Kasko and Eagle Pack, both are good. Lots of sled dog guys up here feed the Eagle Pack.

Purina One is not that good either, but for a store brand, is decent.

If you want super premium food and do not paying about a buck a pound, try Innova or Royal Canine. Both are excellent food, very little waste, no corn, no brewer's rice. Great food.