Puppies and dogs need iron to prevent anemia, just like humans. In some puppy foods, like the one in our Nutro grain free dog food review above, this may be added in as a supplement (iron amino acid chelate) and also through more natural sources such as lentils, peas, and garbanzo beans. Iron works by helping your puppy’s blood cells to carry oxygen, and it works in harmony with both copper and protein for a happy and active puppy!