 Soybeans, one of the most common plant-based protein sources in dog foods, provide a concentrated and complete protein source, meaning that they provide all the essential amino acids in adequate amounts.If soy is excluded for hypoallergenic purposes, chickpeas, green peas, rice, and potatoes are also common ingredients in commercial vegan dog foods.Nutritional yeast is another good source of complete protein, and can also be added to complement the amino acid profile.