As more research is done in the field of veterinary nutrition, we continue to learn more about how to keep pets happy and healthy with one of the most important and enjoyable aspects of their daily care: food.
Research has shown that one of the most critical dietary components for our feline friends is protein. Here’s what you need to know about protein for cats and high-protein diets.
Why Cats Need Protein
There are six classes of nutrients that may be provided by the diet:
Of these nutrients, protein, fat, and carbohydrates can be used as energy sources.
Different species digest and utilize nutrients differently, and therefore have different nutrient requirements. In general, herbivores, or animals that only ingest plants, generally rely more upon carbohydrates for energy than do omnivores (animals that ingest plants and meat), or carnivores (animals that only ingest meat).
Cats Are Obligate Carnivores
Unlike dogs, which are omnivores, cats are obligate carnivores. This means that their bodies have adapted to a diet consisting strictly of meat, which provides animal protein.
Domestic cats are very similar to their wild predecessors and have evolved very little from them. In the wild, a cat’s diet consists of mainly small rodents, such as mice, as well as rabbits, birds, insects, frogs, and reptiles.
A cat’s metabolism is especially suited to a strictly meat-based diet. While herbivores and omnivores can synthesize certain amino acids, which are the building blocks of proteins, cats have more limited ability to do so.
Cats Need Amino Acids From Animal Protein
As a result, cats evolved to ingest specific amino acids that already exist in meat sources because their bodies do not produce enough of them for survival. Cats depend on their diet for many amino acids.
Most species share a need for 9 essential amino acids (amino acids that must be obtained from the diet), but cats require two additional essential amino acids: taurine and arginine. Both taurine and arginine are obtained from eating animal tissues.
Cats are also unable to sufficiently produce certain vitamins that are critical to their health, including niacin, vitamin A, and vitamin D, so they must get them from animal tissues.
Taurine is an amino acid that is particularly important to eye and heart health. It is also necessary for normal reproduction and kitten growth.
Although cats can synthesize small amounts of taurine, they are not able to produce as much as their bodies need.
In the absence of taurine, cats may suffer from blindness due to central retinal degeneration, heart failure from dilated cardiomyopathy, reproductive failure, and/or developmental abnormalities of the central nervous system.
Arginine deficiency leads to high levels of ammonia in the blood, resulting in neurologic symptoms that may quickly lead to seizures and death.
Protein Is a Cat’s Most Important Source of Energy
Cats also use protein for energy. In fact, it is their most important source of energy.
Unlike other species, a cat’s liver enzymes are constantly breaking down proteins for energy and maintenance of blood glucose levels. When cats do not receive enough dietary protein—even when other sources of energy, such as carbohydrates, are present—their bodies start breaking down their own muscle tissue to meet their protein and amino acid requirements.
Common Sources of Protein in Cat Food
There are two main sources of protein used in cat food: animal protein and plant protein. Although vegetarian diets and alternative protein sources may appeal to pet parents, cats are not able to meet their nutritional needs with plant sources alone. Certain nutrients are present only in animal tissues and not in plant products. For example:
Taurine, an essential amino acid for cats, is present in animal tissues but not in plant products.
Methionine and cystine are amino acids that are required in high amounts in cats, especially during growth. Plant sources do not generally provide high enough levels of methionine or cystine for cats. Deficiency of these amino acids can result in poor growth and crusting dermatitis. Kittens require that 19% of their diet consist of animal protein to meet their methionine requirements.
Proteins from animal sources generally have higher biologic availability, and are therefore more readily used by the body than proteins from plant sources.
Common sources of animal proteins in cat food include beef, chicken, turkey, lamb, and fish. In addition to seeing these animal proteins on a label, you may also see different meat meals or meat by-products. And although many pet parents think these are bad ingredients, they actually provide concentrated protein sources.
“Meal” is a term that is commonly seen on pet food labels in reference to the source of animal protein. According to the nonprofit Association of American Feed Control Officials, or AAFCO, the term “meal” denotes animal protein that has been ground and had the water removed.
For example, poultry meal is a dry product produced from whole poultry carcasses and does not contain feathers, head, feet, and entrails. “Meal” is therefore considered an adequate and concentrated protein source.
Meat “by-products” include organ meat. Although many pet parents try to avoid “by-products” when purchasing pet food, by-products can actually provide an adequate and concentrated source of nutrients.
Common sources of plant protein in cat food include corn gluten meal, soybean meal, wheat gluten, and rice protein concentrate.
While some plant sources, such as soybean meal, sunflower meal, and Brewer’s yeast, contain comparable levels of protein to animal-based ingredients, cats are not able to digest and utilize these energy and nitrogen sources as readily as animal proteins.
These sources also do not contain sufficient taurine or methionine. Although synthetic sources of taurine and methionine may be added to some diets, their digestibility is decreased compared to the nutrients that naturally occur in animal tissues.
So, while cats can use plant products and synthetic nutrients as a portion of their diet, they still need to consume animal tissue for adequate life-long nutrition.
Does My Cat Need High-Protein Cat Food?
Adult cats require significantly more protein as a percentage of their diet than dogs or humans. While exact protein recommendations have some degree of variation, adult cats generally need a minimum of 26% protein in their diet, while adult canines require 12%, and humans require 8%.
To put this into the perspective of a cat’s natural diet, a mouse—when measured on a dry matter basis –contains approximately:
It provides approximately 30 kcal of metabolizable energy (ME), which is about 12-13% of a cat’s daily energy requirement.
While AAFCO guidelines recommend a minimum of 30% protein for “Growth and Reproduction” life stages and 26% protein for adult maintenance, an even higher percentage of dietary protein is likely warranted for optimal health.
Recent studies have shown that adult cats that did not consume a diet consisting of at least 40% protein lost lean body mass over time. Some feline diets are 30-38% protein, and diets at this level will result in loss of muscle mass over time. Poor-quality protein, or protein that is less digestible, will result in faster loss of muscle mass than high-quality protein.
Senior Cats Need Increased Protein Levels
As cats age, their protein requirements increase due to reduction in digestive efficiency.
Many cats of 12 or more years of age should be fed a diet containing nearly 50% protein. Many diets formulated for older cats have decreased protein levels due to concerns over kidney disease, which is common in the aging cat population.
While protein restriction may be beneficial for certain cats with kidney disease, a more conservative approach to protein restriction is now recommended and is a topic that should be discussed with your veterinarian.
How Do I Determine How Much Protein Is in my Cat’s Food?
It can be difficult to determine how much protein is in pet food based on the label alone. This is in large part due to variations in the moisture content of food.
The AAFCO Dog and Cat Food Nutrient Profiles base nutrient recommendations on a “dry matter basis,” which means that nutrient percentages are calculated without considering water (moisture) content.
Pet food labels, however, print nutrient content on an “as-fed” basis, which includes water content. This can lead to confusion on the part of consumers, since canned pet food usually contains around 75% moisture, and dry pet food contains about 10% moisture.
So, how do you compare the protein content of cat food when all you have to go off of is the label? The answer is to convert the protein level from an as-fed to a dry matter basis.
Find the Moisture (max) percentage and Crude Protein (min) listed on the pet food label (found in the Guaranteed Analysis section) to perform these calculations:
Subtract the Moisture (max) percentage from 100. This will give you the percent dry matter of the diet.
Divide the Crude Protein (min) by the percent dry matter of the product.
Multiply the result by 100. This will give you the percent of protein on a dry matter basis.
Canned food example:
Canned Food A has the following listed on its label:
12% crude protein minimum
78% moisture maximum
100 – 78 (moisture) = 22 (dry matter of the diet)
12 (crude protein) / 22 = 0.545
0.545 x 100 = 54.5
The percent protein of Canned Food A on a dry matter basis is 54.5%
Dry food example:
Dry Food A has the following listed on its label:
37% minimum crude protein
12% moisture guarantee
100 – 12 (moisture guarantee) = 88 (dry matter of the diet)
37 (minimum crude protein) / 88 = 0.420
0.420 x 100 = 42.0
The percent protein of Dry Food A on a dry matter basis is 42.0%
In this example, it is important to note that by reading the label without considering moisture content, it appears that Dry Food A contains significantly more protein than Canned Food A. However, Dry Food A actually has 12.5% less protein than Canned Food A.
AAFCO Crude Protein Requirements
AAFCO sets standards for pet foods in the United States. While compliance with AAFCO standards is not required for commercial pet foods, most veterinary nutritionists recommend feeding only diets that are AAFCO compliant.
These products will have a nutritional adequacy statement (or AAFCO statement) that states that the diet conforms to one of the AAFCO Dog or Cat Food Nutrient Profiles or Feeding Protocols.
An example of the importance of AAFCO compliance is further illustrated by a discussion of protein analysis. The “Guaranteed Analysis” section of the pet food label contains the percentages of each of the following:
“Crude Protein” is determined based on chemical analysis of all nitrogen-containing sources in the food. Therefore, some non-protein-containing sources, such as urea, can be included in the crude protein content.
AAFCO states that not more than 9% of the crude protein in a diet should be “pepsin indigestible,” meaning that at least 91% of the protein content of AAFCO-approved foods should be digestible protein. Therefore, diets that do not follow AAFCO recommendations may appear to contain adequate protein based on the percentage of Crude Protein; however, this protein may be largely indigestible.
Pet foods that are AAFCO-compliant adhere to more in-depth nutrient profiles that also include recommended amounts of amino acids such as taurine and arginine.
Can Cats Be Allergic to Protein?
Food allergies are fairly common in the feline population. Food allergies may result in symptoms such as:
Allergies to foods are generally triggered by specific proteins within the foods. In order to diagnose a food allergy, a diet trial must be completed. This involves feeding a strictly limited diet, or “elimination diet,” for a period of eight to 12 weeks.
If the diet trial results in a resolution of symptoms, the cat is generally diagnosed with a food allergy.
Elimination diets may take the form of limited ingredient diets or hydrolyzed protein diets. Hydrolyzed protein diets are generally only available with a prescription from a veterinarian. The use of these diets is based on the knowledge that in order to develop an allergy to something, the body must have had prior exposure to it.
Limited ingredient diets work by using proteins that the body has not encountered before and will therefore not have already developed an allergy to. These diets may use protein sources such as duck or venison, which are not included in most commercial diets.
Hydrolyzed protein diets work by modifying the shape of the proteins, so the body does not recognize them as an allergic trigger. They may still contain proteins from common sources such as chicken or fish, but the protein shapes and sizes are modified so they do not trigger allergy receptors.
Cats that respond favorably to a diet trial with a limited ingredient or hydrolyzed diet often continue successfully on the elimination diet. Alternatively, they may undergo a diet “challenge,” were they are introduced to other protein sources with close monitoring as to which sources do and do not trigger the allergies.
Pet parents must consider many different factors when selecting a diet for their feline companions. Often, multiple sources of information may seem overwhelming and can make decision-making even more difficult. However, one of the most important things for cat parents to remember is that protein is a critical nutrient to consider when planning the diet of these obligate carnivores.
Featured image: iStock.com/gornostaj
“AAFCO Methods for Substantiating Nutritional Adequacy of Dog and Cat Foods: AAFCO Dog and Cat Food Nutrient Profiles.” www.aafco.org, 2014.
Burns, Kara M., “Feline Nutrition – Cats Are Not Small Dogs!” Southwest Veterinary Symposium, September 21-24, 2017, San Antonio, TX.
Davenport, Gary M., “Feeding Cats as Carnivores.” Iams Company Symposium Proceedings, 2002.
Kerby, Victoria L., “Feeding Our Feline Overlords: Nutrition for the Internet’s Favorite Animal.” Western Veterinary Conference, February 16-19, 2020, Las Vegas, NV.
Scherk, Margie, “Feline Nutrition: Facts, Fun and Physiology, Cats Are Different Than Dogs!” American Board of Veterinary Practitioners Symposium, April 15-18, 2010, Denver, CO.
Thomas, Randall C., “Food Allergy in Dogs and Cats.” Western Veterinary Conference, 2005.
Verbrugghe A. and S. Dodd, “Plant-Based Diets for Dogs and Cats.” World Small Animal Veterinary Association Congress Proceedings, July 16-19, 2019, Toronto, Canada.
Zoran, Debra L., “Cats and Protein: The Conversation Continues.” American College of Veterinary Internal Medicine Forum, June 14-16, Seattle, WA.