Comparing dog food ingredients, once you look at the paragraph on the side of the bag, may seem like it requires a PHD to decipher. Protein meals, by-products and tocopherols abound. Many authorities on dog food and nutrition recommend that buyers avoid any dog food containing by-products while others eschew grain based products. Understanding dog food ingredients and their legal definitions as well as the guaranteed analysis will help you to better compare dog foods and find the best value and nutritious diet for your four legged companion. Dog Food Ingredients Comparison 101: The ingredients are listed on the food packaging by their weight, in descending order. Ingredients are listed on an “as fed basis,” which can make interpretation of ingredient lists difficult, as key ingredients are regularly added with differing moisture contents. Meats contain more moisture which results in greater weight per volume, and therefore they may be listed first on the ingredient list.