I figured that it may be a good idea that we get a basic understanding of protein with it’s typically used definitions and elements before we continue a discussion of various view points on canine protein and protein requirements. So I tried to come up with the following and hope it is not too boring nor confusing.
The AAFCO Nutrient Profiles for Dogs include recommendations for Crude Protein and 10 Essential Amino Acids, Crude Fat, Linoleic Acid (Omega-6 fatty acid), 12 Minerals and 11 Vitamins. This article today focuses on protein, I will address the other nutrients at a later point.
AAFCO’s protein details are: Protein, amino acids to include arginine, histidine, isoleucine, leucine, lysine, methionine cystine, phenylalaline tyrosine, threonine, tryptophan and valine.
Nutrient Profile values are expressed on a DM or Dry Matter basis to support efforts in accurately comparing various foods with various different moisture content. DM is also more meaningful related to the nutrient content of a food as water (or moisture), while an important nutrient, contributes no caloric value. Ironically, AAFCO labeling requirements allow for the nutrient content to be shown as “as fed” basis thereby including the moisture present in the food.
While the AAFCO regulations reflect minimum and maximum nutrient content, protein requirements vary from species to species, and specifically during the rapid growth stages of a puppy and for senior animals. Pregnant and lactating dogs require the same amounts as a puppy. Sick, weak or debilitated dogs usually need additional protein. Dogs with compromised kidneys may need to be restricted on their protein intake and require a high biological value diet If a dog has kidney problems excessive protein is definitely not recommended. This also brings up the question if a dog can be over fed with protein. The answer is yes and no. In a healthy dog excessive protein intake gets excreted into the urine, used as calories or is converted to fat and usually does not cause any harm. The answer to this question is important as protein is the most expensive nutrient in a food and you do not want to pay more than what you actually need. Most dog foods available on the market have a protein content based on the AAFCO minimum with a security cushion of a couple percent built in.
Proteins are the building blocks in animal nutrition and one of the most important nutrients in the diet. They also are one of the nutrients most widely debated. For around twenty thousand years as dogs, and for several million years before that as wolves, the only problem canines had with protein was getting enough of it. Dogs primarily lived on meat diets thereby consuming high percentages of their food as protein. Along with that they also took in a fair portion of fat, a little fiber and carbohydrates, but the primary food was meat. Felines were similar however they were even stricter carnivore not eating any carbohydrates. The discussion about protein originated when commercial dog foods became widely available and started replacing the traditional meat and meat byproduct diet. Initially the cheaper forms of leftover meat made up the food with little regard for flavor or fashion. With the interest in health as related to diet, a whole new generation of dog foods has entered the market. These quality foods challenge the earlier foods by promoting a product that is better than ever for our companion animals. At the center of debate for the newer products is protein, its source, digestibility, and quantity.
Protein is made up of amino acids which are chemical units or building blocks. They are an integral part of every living cell in an animal’s body. Protein is necessary for the formation of healthy cells, enzymes, hormones and a variety of body secretions, ligaments, tendons, organs and protective tissues. Next to water, protein makes up the majority of an animal’s body weight. The body can manufacture some of the total 28 amino acids needed, but others must be provided in the food. They are called “essential amino acids”. A dog’s natural diet consists typically of approximately 55% protein deriving from meat. The problem with protein is that AAFCO does not require a manufacturer to list what type of protein makes up “crude protein”. Thus, dogs may be consuming too much indigestible protein, i.e. protein deriving from sources like for example grain. Good, high quality animal source proteins provide superior amino acid balances compared with the amino acid balances supplied by grain based sources.
The word protein comes from the Greek word “proteios” = "primary". Proteins were first described and named by the Swedish chemist Jöns Jakob Berzelius in 1838. However, the central role of proteins in living organisms was not fully appreciated until 1926, when James B. Sumner showed that the enzyme urease was a protein. The first protein to be sequenced was insulin, by Frederick Sanger, who won the Nobel Prize for this achievement in 1958. The first protein structures to be solved included hemoglobin and myoglobin, by Max Perutz and Sir John Cowdery Kendrew, respectively, in 1958. The three-dimensional structures of both proteins were first determined by x-ray diffraction analysis; Perutz and Kendrew shared the 1962 Nobel Prize in Chemistry for these discoveries.
But aside from all that history, why do animals need protein? Proteins are necessary for all aspects of growth and development and are very important in structural make up and the immune system. In addition, they are burned as calories and can be converted to and stored as fat. In reality, our pets do not need the protein but they need the building blocks that make up the protein, which are the so called amino acids.
Amino acids combine in a condensation reaction that releases water and a new "amino acid residue" that is held together by a peptide bond. Proteins are defined by their unique sequence of amino acid residues; this sequence is the primary structure of the protein. Just as the letters of the alphabet can be combined to form an almost endless variety of words, amino acids can be linked in varying sequences to form a vast variety of proteins. Twenty standard amino acids are used by cells in protein biosynthesis, and these are specified by the general genetic code. These 20 amino acids are biosynthesized from other molecules, but organisms differ in which ones they can synthesize and which ones must be provided in their diet. The ones that cannot be synthesized by an organism are called essential amino acids, versus the alpha amino acids, which can be synthesized by the body.
Stay tuned for Part 2b when I am going to address amino acids in more detail.