The Dog Food Project
No matter how little money and how few possesions you own, having a dog makes you rich. - Louis Sabin
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Proteins (includes amino acids)

Proteins are a group of complex organic macromolecules that contain carbon, hydrogen, oxygen, nitrogen, and in most cases also sulfur. They are formed by one or more chains of amino acids - which are the individual "building blocks" for tissues, organs, enzymes, hormones, antibodies etc. The proteins consumed in the diet must be broken down into their individual amino acids by the digestive system, so the body can then "reassemble" them to build, rebuild or replace above mentioned cells.

Amino acids are divided into two groups:

  • Essential amino acids: cannot be synthesized by the body in sufficient quantities and must be supplied in the diet. For dogs, these include Arginine, Methionine, Histidine, Phenylalanine, Isoleucine, Threonine, Leucine, Tryptophan, Lysine and Valine. (For cats, Taurine is also essential, humans can synthesize both Arginine and Taurine.)
  • Non-essential amino acids: are synthesized by the body if sufficient "building material" is available, which is usually the case if a balanced diet is fed.

Proteins are derived from different animal and plant sources, and depending on these sources their amino acid profiles are more or less complete. Amounts, balance and quality of the essential amino acids are very important in a dog food, if one or more are not supplied in sufficient quantity or missing entirely, the ingredients can be of the best possible quality yet will not keep an animal healthy and thriving. The amino acid profile of a protein source is considered "balanced" when it contains both essential and non-essential amino acids in proper amounts and proportions required by the dog's body, however, it is possible to combine two or more less complete protein sources that complement each other and result in a well rounded, balanced food product.

Aside from a properly balanced amino acid content, the digestibility of the protein sources is also very important. In fact, it is more important than the actual protein content of the product because the amount of digestible protein is what counts for proper nutrition, not the amount of "crude" protein.. What would you rather feed, a food with a protein content of 30% that is 60% digestible, or one with a protein content of 22% that is 95% digestible?

Eggs, muscle and organ meats are the most complete, most digestible sources of protein and should be the main ingredients in a quality food, preferably as a "meal" form with most of the water already removed. Some grains, grain byproducts and other vegetable sources also contribute protein, but those are generally less complete and not as digestible.

Looking at the above paragraphs, I do not understand why there is this common misconception that dogs should eat a low-protein diet - unless they suffer from some sort of illness that would require restricted amounts of protein. Not being active, pregnant, lactating or a "working dog", for which high protein diets are usually only recommended, doesn't mean the body doesn't require those "building blocks" to maintain and rebuild itself.

While it is true that (particularly large breed) puppies benefit from a moderate protein content diet during their growth stage, in order to allow for slower, more even growth and to avoid orthopedic problems, the concept of avoiding proteins and fats in a dog's diet seems to be tied more to cost of ingredients - lesser amounts of quality meats, more grains - than anything else. Wanting to secure their profit margin, the "big players" in the pet food industry seem to be marketing their products based on least-cost ideas of "proper nutrition", impressing wrong dietary principles on consumers who are just trying to do the right thing for their beloved pets.

When feeding a diet that contains more protein than currently needed, extra protein is metabolized and used for energy. Unlike fat, excessive protein is not stored as such in the body, but once the demand for amino acids is met and protein reserves are filled, protein energy could be used for the production of fat. Animals fed diets too low in dietary protein may develop deficiency symptoms like decreased appetite, poor growth, weight loss, a rough and dull coat, and decreased immune function. Lower reproductive performance, and decreased milk production are symptoms in breeding animals.

There is no scientific proof that high protein diets cause dogs to get "hyper" or "aggressive". No biochemical or nutritional factors support this myth. There is also no conclusive evidence so far that protein intake actually contributes to the development of kidney dysfunction in healthy animals.