Our last bit on nutrition topics for now......
Myth #7: By-products are bad ingredients and must be avoided
Some food companies will try to convince you that by-products are nothing but junk, undesireable leftovers that have no nutritional value and may include things such as hooves and horns. This is blatantly false. By-products are cleaned and processed organ meat that by law and definition must specifically exclude hair, horns, hooves, skin, feathers, and gastrointestinal contents. Ingredients defined as by-products can include lungs, spleen, kidneys, liver, blood, stomach, intestines, and other organs. While we may not typically eat these parts of animals, these other organs contain important nutrients, some of which are not found in muscle tissue. By-products are included in pet foods because they are lower cost sources of good nutrients, not as "filler".
Myth #8: Over-the-counter "restricted ingredient" diets are sufficient for food allergies
Food allergies are triggered by exposure to a protein and/or carbohydrate source to which a pet has a sensitivity. The treatment in these cases is to eliminate exposure of these ingredients in a pet's diet. Typical commercial diets may not include these components on a label or in the recipe, but that doesn't mean that the allergens are not present. Several studies have shown trace ingredients in pet foods that were not listed on the label. This is not a problem for an average dog or cat, but for one with confirmed food allergies it could be enough to trigger a reaction. Just because "chicken" isn't listed on the label doesn't mean that there can't be trace amounts in the diet. This finding is why veterinary dermatologists always recommend more strictly controlled "prescription" diets when diagnosing and treating food sensitivities.
Myth #9: Lamb and rice diets are better for a pet's skin
This myth derives from a misconception about food ingredients and allergies. When a pet has a reaction to food you will typically see symptoms related to the skin: hair loss, itching, skin infections, etc. The way to resolve the problem is to feed a diet that eliminates the allergens and replaces them with ingredients to which the pet has never been exposed. Many years ago we would use diets that had lamb as the protein source and rice for carbohydrates, as dogs and cats rarely ate these ingredients. Because the allergens were eliminated the pet's skin would improve, but this only happened because the pet was allergic to other foods and not due to inherent qualities of the ingredients. Currently lamb and rice are common in pet foods and are no longer considered good "hypoallergenic" diets because many pets have been exposed to them. These components are no better or worse for an average pet than any other protein or carbohydrate, and for most pets won't give any benefit compared to other ingredients.