While some foods do not have enough good ingredients, other issues like malabsorption can play a part too. This means that the quality of proteins do not allow for sufficient absorbtion of the protein OR the dog is missing something (enzymes) that does not permit him to absorb all that is available to him.
In addtion to improving the quality of the food you are serving I would add something like 'Prozyme' to his food. This will ensure that he is getting everything he can from the food you serve. It helps him to break down the food into usable form.
Love Them & Lead Them,
~Elizabeth & Doug
Dog Training the Way Nature Intended