Proteins & raw diet for cats

This article is part of the series in which we explore the science of nutrition. After water and energy that we addressed in the previous articles in the series, it is now time to talk about macronutrients. In today’s article, we are going to discover one of the three macronutrients: proteins. We will see what they are, what the feline requirements are, and we’ll talk about other controversial subjects such as protein excess.

What are proteins?

Proteins are molecules made of amino acids linked together in a chain.
Proteins have various functions as they are structural components of various tissues such as hair, skin, muscles, bones, nails, tendons, ligaments, and cartilages... On top of that, all the enzymes for the many metabolic reactions of the body (like digestion) are proteins, as well as many hormones like insulin. The immune system also relies on proteins: antibodies are, in fact, large protein molecules. [1]
In the tissues, proteins are constantly degraded and replaced which explains why the body needs proteins. However, as the body is able to synthesize proteins from amino acids, it can be said that the body doesn’t have a requirement for proteins per se but for amino acids. However, as in practice diets contain proteins and not individual amino acids, the requirement is still expressed as a protein requirement. [1]
Of the amino acids, 11 are essential: these must be supplied in a cat’s diet, as cats are not able to synthesize them to meet their body’s needs.
The 11 essential amino acids are the following: arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine, and taurine. Taurine isn’t essential for dogs but it is for cats and I dedicated an entire article about it.
As we have seen in the article about energy, in addition to their different metabolic roles, proteins can be used to supply energy to a cat. One gram of protein provides 3.5 kcal to 4 kcal, depending on the digestibility of the diet.
Proteins are also a source of flavor in the diet: increasing the protein content of a diet generally increases palatability. [6]

Proteins quality

Not all proteins are created equal. In fact, they vary in quality: they are not all used as efficiently by the body. There are different ways to define if a protein is high-quality or low-quality. Protein quality depends on many factors; three important contributing elements are the amino acid profile of the proteins, digestibility, and biological value. [1]

Amino acid profile

The amino acid profile is the repartition and proportions of the amino acids in a protein. High-quality proteins contain high quantities of essential amino acids and—in particular—lysine, methionine, and tryptophan.

Digestibility

Digestibility refers to the ability of the body to break down the proteins of the food into amino acids. It’s influenced by several parameters like the processing time or the fiber content of the food. For example, overcooked proteins form Maillard products which are indigestible and harmful components (we already mentioned them in the taurine article): in this case, the protein digestibility would be reduced. High-fiber diets (> 10% of fiber on the dry matter) decrease protein digestibility by preventing their absorption.
As we have seen in the article about the benefits of a raw diet, when undigested proteins reach the large intestine, they are fermented into putrefactive compounds. These compounds give the feces their bad odor. In the case of raw diets—as the proteins are highly digestible—there is less odor in the stools.

Biological value

The biological value of proteins evaluates the ability of the body to convert the absorbed amino acids into tissues. It’s different from digestibility: in the case of an indigestible protein, if the small amount of protein that is absorbed is used highly efficiently, the biological value will be high, and vice versa. [1]

Some examples of animal protein sources are meat, organs, fish, eggs, animal meals, fish meals, blood meals, casein…
Some examples of plant-based protein sources are corn gluten meal, wheat gluten, soybean meal, canola meal, peas, peas protein isolates...
Animal proteins are generally of better quality than plant proteins as they have a better biological, digestibility, and amino acid profile than plant proteins. [1][11]

Protein requirement: Why commercial diets don’t always contain enough protein

Protein requirement is dependent on several factors such as the life stage of the cat, the energy density of the diet, the quality of the proteins, etc…
In fact, growing kittens, gestating or lactating females have higher protein needs than adult cats as they need to create new tissues.
As we have seen in the article about energy, nutrient requirements depend on the amount of food that a cat eats, which itself depends on the energy of the diet. If the diet is high in energy, the cat will eat less of it and so the protein amount in the diet needs to be higher.
Finally, if the quality of the proteins is low, the requirement for proteins will be higher. In fact, if in a diet the profile of the amino acids is not adequate or if the protein digestibility is too low, the cat will need to eat more of it to get the same result compared to a diet composed of high-quality proteins. [1]

Now, let’s look at the numbers for the minimum protein recommendation:

• The current NRC recommendation (published in 2006) is 50 g per 1000 kcal, which is equivalent to 20% proteins on the dry matter (DM) for a 4000 kcal/kg diet.

• The AAFCO recommendation is 65 g per 1000 kcal, which is equivalent to 26% proteins on the DM.

• The FEDIAF recommendation is 62.5 g per 1000 kcal, which is equivalent to 25% proteins on the DM.

To give you a better idea of what this means, for your own cat this is roughly equivalent to 3 to 4 grams of protein a day per kg of your cat (or around 20 to 30% of calories coming from proteins).
However, a more recent study (published in 2013) which used another methodology to estimate the protein requirement arrived at a conclusion of 5.2 g of daily proteins per kg of cat. This would be roughly equivalent to 81 g per 1000 kcal, or 32% of proteins on the DM, or 30 to 40% of calories coming from proteins. [5]
This value is closer to what wild cats would eat as around 50% of their calories come from proteins. [4] Moreover, in studies, when cats are allowed to choose between several foods with different protein content, they will also choose around 50% of their calories coming from proteins. [6][8][9]
So, the current official recommendation underestimates the protein requirement of cats: I would then recommend feeding at least 5.2 g of protein per kg of cat, per day. Additionally, it seems that cats are metabolically adapted to having a proportion of 50% of their calories coming from protein. [3][10]

If you are feeding kibble

Because the actual protein requirement of cats is higher than the official recommendation, it’s possible that a “balanced and complete” food may be, in fact, deficient in proteins. If you are feeding kibbles and they contain less than 30% of proteins (on an as fed basis) they are likely deficient in proteins.

What are the consequences of a protein deficiency?

The main consequences of a protein deficiency are retarded growth in kittens, weight loss, reduced lean body mass. This might result in muscle loss, brittle hair, and a poor coat. The protein deficiency is often combined with an energy deficiency: in that case, a cat would also be lethargic, have a compromised immune system, and have a reduced digestibility efficiency.

Protein excess: is too much protein bad?

There is no toxicity associated with feeding a high protein diet. Historically, it was believed that feeding a high-protein diet, above the protein requirement, would lead to kidney damage, especially in older pets. However, this theory has now been disproven. [1]
On the contrary, healthy older pets can benefit from having a diet slightly higher in high-quality proteins as it helps them to keep their lean body mass and avoid muscle wasting. [1]
On the sensitive subject of kidney disease, what can lead to kidney damage is high levels of phosphorus, but we will explore this subject in more detail in a future article. Moreover, dietary protein restrictions for cats with chronic kidney disease remain controversial in the veterinary world. [7]

“Contrary to popular belief, there is no research-based, conclusive evidence that protein ingestion contributes to the development of kidney dysfunction in healthy dogs and cats. Moreover, there is no evidence that the protein intake of geriatric pets should be restricted just because of old age”

Quote from Canine and Feline Nutrition by Linda P. Case et al.

Protein in a raw diet

Most of the time, protein content is not a concern in a raw diet as raw meat contains high-quality and easily digestible proteins. Similarly, amino acids are very rarely a concern in raw diets, with the exception of taurine. Taurine content can be below the required amounts if you use only meats low in taurine like chicken breast and rabbit. Grinding the meat can also reduce the amount of taurine: for more details on this subject, I recommend that you read my article dedicated to taurine.

However, be mindful of the fat content in the diet. Meats that are high in fat (>15% on an as-fed basis or >250 kcal/100 g) often have a protein content lower than 80 g per 1000 kcal. Examples of meats high in fat are ground beef (20% or 30% fat), lamb shoulder, beef brisket, or duck breast with skin.
Lean meats which contain 5% of fat or less (or <150 kcal/100 g) generally have a high protein content, greater than 150 g per 1000 kcal. Examples of lean meats are chicken breast, venison, pork tenderloin.
Meats moderate in fat at around 10% fat (between 175 kcal/100 g), generally have a protein content of around 120 g per 1000 kcal. Examples of meats moderate in fat are chicken breast with skin, ground beef at 10% fat, quail.
At the end of this article, you will find the protein amount for different cuts of meat.

To conclude, proteins are essential for cats and should be of high quality. Protein content and amino-acid profile are not a concern in raw diets except if the diet is high in fat.
However, concerning industrial pet food, the current official recommendations seem to be too low in comparison to the feline protein requirements. If you feed kibbles, you need to make sure that they contain at least 30% of proteins.
Finally, protein excess is not harmful to cats, and older pets don’t need a diet reduced in proteins.

Protein in raw meat

Cut	g of proteins / 100g as fed	g of proteins / 1000kcal
Chicken breast	22.5	187.5
Chicken breast with skin	20.9	121.2
Beef brisket point	17.7	66.1
Beef chuck stew meat	21.8	169.9
Ground beef 10%	20.0	113.6
Ground beef 20%	17.2	67.6
Ground beef 30%	14.4	43.2
Duck breast	17.9	52.6
Lamb shoulder chop	16.8	64.6
Pork tenderloin	20.7	172.1
Pork leg shank	19.9	103.0
Turkey breast	23.3	204.7
Turkey thigh with skin	19.5	121.4
Veal escalope	20.7	191.7
Veal shoulder	20.7	166.9
Venison	23.0	191.3

If the number is in yellow, the cut contains less 80 g of proteins per 1000 kcal, it’s less than the recommendation of the 2013 study. Generally these meats are high in fat (>15%)

If the number is in light green, the cut contains around 120 g per 1000 kcal, generally these meats are moderate in fat (~10%).

If the number is in dark green, the cut contains more than 150 g per 1000 kcal, generally these meats are lean and contain 5% of fat or less.

Sources

[1] (2015). Canine and Feline Nutrition (Linda P. Case et al.).
[2] National Research Council. 2006. Nutrient Requirements of Dogs and Cats. Washington, DC: The National Academies Press.
[3] Eisert R. Hypercarnivory and the brain: protein requirements of cats reconsidered. J Comp Physiol B. 2011;181(1):1-17.
[4] Plantinga EA, Bosch G, Hendriks WH. Estimation of the dietary nutrient profile of free-roaming feral cats: possible implications for nutrition of domestic cats. Br J Nutr. 2011;106 Suppl 1:S35-S48.
[5] Laflamme DP, Hannah SS. Discrepancy between use of lean body mass or nitrogen balance to determine protein requirements for adult cats. J Feline Med Surg. 2013;15(8):691-697.
[6] Hewson-Hughes AK, Colyer A, Simpson SJ, Raubenheimer D. Balancing macronutrient intake in a mammalian carnivore: disentangling the influences of flavour and nutrition. R Soc Open Sci. 2016;3(6):160081. Published 2016 Jun 15.
[7] Scherk MA, Laflamme DP. Controversies in Veterinary Nephrology: Renal Diets Are Indicated for Cats with International Renal Interest Society Chronic Kidney Disease Stages 2 to 4: The Con View. Vet Clin North Am Small Anim Pract. 2016;46(6):1067-1094.
[8] Salaun F, Blanchard G, Le Paih L, Roberti F, Niceron C. Impact of macronutrient composition and palatability in wet diets on food selection in cats. J Anim Physiol Anim Nutr (Berl). 2017;101(2):320-328.
[9] Allaway D, de Alvaro CH, Hewson-Hughes A, Staunton R, Morris P, Alexander J. Impact of dietary macronutrient profile on feline body weight is not consistent with the protein leverage hypothesis. Br J Nutr. 2018;120(11):1310-1318.
[10] Alice S. Green, Jon J. Ramsey, Cecilia Villaverde, Danny K. Asami, Alfreda Wei, Andrea J. Fascetti, Cats Are Able to Adapt Protein Oxidation to Protein Intake Provided Their Requirement for Dietary Protein Is Met, The Journal of Nutrition, Volume 138, Issue 6, June 2008, Pages 1053–1060.
[11] Funaba M, Oka Y, Kobayashi S, Kaneko M, Yamamoto H, Namikawa K, Iriki T, Hatano Y, Abe M. Evaluation of meat meal, chicken meal, and corn gluten meal as dietary sources of protein in dry cat food. Can J Vet Res. 2005 Oct;69(4):299-304.

Sources for the table

USDA

CIQUAL