Protein is found in most foods, including carbohydrates. But dogs are carnivores and the best source of protein for them is found in animal products. This would include meat (pork, beef, poultry, lamb, rabbit, fish, dairy and eggs, just to mention a few). Animal based proteins contain a complete amino acid profile needed by carnivores. Plant based proteins are missing important amino acids, including taurine and carnitine. Both of these are important for heart and organ health.
The anatomy and digestive process of dogs are designed to most easily digest animal fat and protein. Dogs perform best on animal based products. Studies have shown you cannot feed a dog too much protein.