I wonder if there is a supplement I could feed to one of my very old cats which would make him absorb more nutrients from the food he eats. He is always hungry and although I feed him, alot, (canned cat food, tuna, canned chicken and dry food), he seems to not be putting on weight. He has gone from 12 lbs to 7.5 lbs over the past few years. He is a Russian Blue and is definitely 15+. Since he is probably in his end years, I won't take him to the vet for this. Wonder if someone has some information to share.