Protein in pet foods
What is protein
Proteins are the building blocks of the body and therefore essential for the daily function. Within the body, proteins have numerous functions. They are the major structural components of hair, feathers, skin, nails, tendons, ligaments and cartilage.
Proteins are required in the diet to provide a source of amino acids, to build, repair and replace body proteins. Amino acids are divided into two groups: essential and nonessential. The difference between these two groups is that essential amino acids must be provided through the diet whereas nonessential amino acids can be synthesized by the body. Out of 22 amino acids, 10 of them are essential to dogs and 11 are essential to cats. Some of the more important amino acids are arginine, lysine, methionine, tryptophan and taurine. Arginine and taurine are only present in animal proteins such as meat, which is why both dog and cat food must contain some degree of animal protein.
The concentration of essential amino acids and digestibility is what determines the quality of a protein. Proteins of good quality ensure the animal ideal proportions of essential amino acids, whereas the animal does not properly digest poor quality proteins. Good quality proteins are more bioavailable for pets, and can better be absorbed by the body, thus the quality of the protein should be more important than the actual amount. In other words, the higher the quality of the protein the less quantity will be needed by the animal to meet all its need for essential amino acids. Poultry, meat, fish and eggs are generally considered good-quality proteins. A diet of 10 % high-quality protein (meat or eggs) equals a diet containing 22 % protein derived from cereals. In pet foods, multiple protein sources are often combined to improve the overall quality and content of amino acids.
A common misconception among pet owners is the fact that pets require diets consisting almost purely of meat. This, however, is not true. The reason for this is probably that many pet food companies have used marketing tactics to make pet owners believe in high protein diets, but the truth is that high protein diets can be harmful to pets. According to new European legislation, pet food companies are no longer allowed to declare the meat percentage in their products, but only the percentage of protein that has an animal origin. This can be a problem in some cases because the percentage of protein in a product does not state anything about neither the quality nor the source of protein, which is the most important thing to be aware of.
The AAFCO (The Association of American Feed Control Officials) has established that canine pet foods containing good quality protein sources should contain at least 22 % for growth and 18 % for maintenance. For commercial cat foods, AAFCO recommends a protein content of at least 30 % for kittens and 26 % for adult cats. These recommendations are daily allowances and should not be seen as minimum requirements or optimal intake levels. There is no scientific evidence that increasing the amount of protein is better as long as the daily requirements are met. On the contrary, there are several health issues to be aware of when choosing high protein diets for your pet. Thus, recommendations are that protein content in maintenance pet foods for adult animals do not exceed 30 % for dogs and 45 % for cats.
When pets eat too much protein they cannot use it all at the same time. Excessive amounts of protein cannot be stored in the body for later use, and therefore the animal will have to excrete it through the urine via the kidneys. This means that if a pet is fed high protein diets for a long period there is a risk of overloading the kidneys and the development of kidney disease. Another issue is that protein is a nutrient very high in calories, so when feeding high protein diets there is a greater risk of the animal becoming overweight. Finally, high protein diets also make it difficult to maintain the right calcium-phosphorus ratio and this is especially a problem for puppies and kittens because it can lead to abnormal joint and bone development predisposing the animals for arthritis in the future.
Excess protein is found in pet foods for several reasons. Dogs are omnivorous by nature, but some pet food companies have raised the myth that dogs are carnivorous and that high-protein meat-based diets are more natural and better. Another marketing stunt used by some pet food producers is that high-protein diets build more muscle and a thicker coat. All of these marketing statements contribute to the mistaken perception that high-protein pet foods equal high-quality pet food.
As a pet owner, one should also be aware that excess protein makes the food more expensive. Dogs and cats use some of the excess protein for energy. However, this is a much more expensive energy source than e.g. carbohydrates which is also a better source of energy for the dog and cat. All aspects taken into account, there is no nutritional nor scientific reasons supporting giving pet excessive amounts of dietary protein.