Dogs love meat, and they need protein. Unlike cats, which need high amounts of protein and no carbohydrates at all, most dogs can easily tolerate a diet that contains 50 percent carbohydrates (or even more). Still, Whole Dog Journal, DogFoodAdvisor.com, and most other experts point out that dogs don't actually need carbs at all. The other side of the coin is that carbs aren't bad for a dog, either, and provide some benefits, such as a short term burst of energy. They also are useful in processing dry kibble and in keeping down the cost of a pet food. Still, as DogFoodAdvisor.com notes, the best foods are those that are "rich in meat-based protein and lower in carbs."
If you've read any dog food labels, you might have noticed the term "by-product." Meat by-products consist mainly of animal parts that are not used for human consumption, such as bones, organs, blood, fatty tissue and intestines. If a label says "chicken by-product," all the parts must come from chicken; the same goes for lamb, beef, etc.
There are two schools of thought when it comes to by-products in dog food. Some say that because a dog in the wild would eat the entire animal when killing prey, including skin, organs and bones, some amount of by-product in dog food is just fine. The other school of thought is that by-products should be avoided entirely, and that a dog's diet should contain meat, vegetables and absorbable grains. These critics say that it's simply too hard to know what exactly is included in by-products.
Even reviews that say by-products are fine say that dog owners should look for specific origin, such as chicken by-product or lamb by-product. Note that in poultry-based dog foods, the term "by-product" is used to identify by-product meals. However, in other types of dog food, by-product meal can be labeled as "meat and bone meal" (MBM) or even "beef and bone meal." This type of labeling is legal, but clearly misleading.
While you'll want to see meat at the top of an ingredient list in any canned or raw/dehydrated food, seeing it at the top of the list in a dry kibble is also a little misleading. That's because meat has a high water content that is removed when processed into dry pet food, so there might actually be less "meat" than there is of some ingredients that are listed lower down. However, specific meat meals, such as chicken meal or beef meal, are the named meat with the water removed, and finding them high up in the ingredient list is a good indication of a high-protein dry food.
The quality of the carbohydrate sources also matters. High-quality grains, such as brown rice, provide good nutritional value, but other grains deliver less of what dogs need in their diet. Corn, in particular, is the target of some scorn among pet-food advocates. Mike Sagman at DogFoodAdvisor.com looks at the pros and cons -- mostly cons -- of corn in dog food. Glutens are another group of ingredients that experts say don't provide much nutritional value to dogs and are a particular concern since 2007's massive recall of pet foods tainted by contaminated wheat and rice gluten from China.
Dog food companies are making moves to get away from using artificial preservatives in dog food. Chemicals used as preservatives, like BHA, BHT and ethoxyquin, have been under scrutiny, and many companies are switching to natural preservatives like vitamin C (ascorbate) and vitamin E (tocopherols). Naturox, which is made from natural ingredients, is also gaining in popularity as a preservative. Reviews say natural preservatives are much safer. Ethoxyquin has been of particular concern to some because it is also used to preserve certain ingredients -- mainly fish meals -- before they reach the pet-food maker, and hence would not be included on ingredient lists.
Propylene glycol is another controversial ingredient that is found in a host of dry dog foods. It's used to give kibble a moist texture. Lots of alarms have been raised because it's easy to confuse propylene glycol with ethylene glycol. Though both are used in antifreeze products, propylene glycol is considered to be non-toxic-- so much so that it's FDA approved and used in a lot of human foods as well, such as fat-free ice cream, cake mixes, packaged cakes, frostings, dyes, flavorings and more. Propylene glycol is known to be toxic to cats, but experts can't point to any hard evidence that propylene glycol is dangerous to dogs. Still, many pet food advocates say that they'd rather not take the risk.