Welcome to Tasty Tidbits, our series dedicated to exploring the essential nutrients that keep pets healthy and thriving. In this installment, we’re diving into protein and amino acids—the foundation of growth, repair, and vitality. Whether you’re a pet owner looking to make informed choices or a veterinary professional in training, understanding these nutrients is key to supporting optimal health.
Why Protein Matters
Protein is more than just a dietary component—it’s the structural backbone of your pet’s body. Composed of amino acids, protein builds muscles, organs, skin, fur, and nails. It also plays a critical role in immune function and metabolic processes. Without adequate protein, pets can experience muscle wasting, poor coat quality, slowed growth, and even organ dysfunction.
Protein requirements vary by life stage. Puppies, kittens, and reproducing animals need more than adults. Complete and balanced diets formulated for these stages ensure adequate intake. Protein levels and sources are especially important for pets with certain health conditions. Excess protein can place additional strain on the liver and kidneys. The type of protein used can also influence the outcomes of food sensitivities.
What Are Amino Acids?
Amino acids are the building blocks of protein. Some are non-essential, meaning the body can synthesize them, while others are essential, meaning they must come from the diet. The essential amino acids for cats and dogs are:
- Arginine
- Histidine
- Isoleucine
- Leucine
- Lysine
- Methionine (+Cysteine)
- Phenylalanine
- Threonine
- Tryptophan
- Valine
- Taurine – Essential for cats only
When cats and dogs consume protein, they have to break them down into small peptides (short chains of amino acids) or individual amino acids using gastric acid and enzymes in the gastro-intestinal tract. This allows the cat and dog to absorb these amino acids or short peptides into the blood stream. They can then be rebuilt into proteins and other molecules needed by the animal.
But the process of building proteins for the body can only occur when all the necessary amino acids are readily available. If cats and dogs don’t consume enough amino acids through their diet, they must obtain them elsewhere. This means that they will begin to break down other proteins in the body to supply the amino acids needed.
Therefore, we need to ensure that cats and dogs have adequate intake of proteins, and more specifically, the amino acids. Each essential amino acid has a unique role in health, and deficiencies can lead to serious consequences. Let’s explore them one by one.
Protein
Role in the Body:
Protein is an essential macronutrient composed of a variety of amino acids. Protein is vital for the growth, repair, and maintenance of body tissues and is the primary component of muscles, organs, fur, and nails!
Nutritional Sources:
There is no shortage of options when it comes to nutritional sources of protein. Some animal-based protein options include chicken, beef, fish, and eggs. Some plant-based options include soybeans, peas, lentils, and quinoa.
Amount Needed in the Diet:
Protein is needed in various amounts depending on the specific needs of your pet. Choosing a complete and balanced diet formulated for your pet’s life stage will provide an adequate amount. Pets that are growing or in a phase of reproduction will have higher protein requirements than adults.
Deficiencies:
A deficiency in protein can lead to serious health issues. Without enough protein, cats and dogs may experience muscle wasting, slow growth, poor coat quality, weakened immune function, and even organ dysfunction.
Toxicities:
Healthy pets generally tolerate high protein well, but pets with kidney disease, liver disease, or digestive sensitivities may need controlled levels. Additionally, the type of protein used can influence the outcomes of food sensitivity.
Arginine
Role in the Body:
Arginine is an essential amino acid that supports protein synthesis and elicits the release of hormones. Arginine is also the precursor of nitric oxide, an important neurotransmitter in many bodily systems, such as the cardiovascular system and immune system!
Nutritional Sources:
Arginine can be found in plant sources such as whole grains and legumes. It is also present in animal sources such as red meat, poultry, dairy, and eggs.
Amount Needed:
Arginine is needed in various amounts depending on your pet’s life stage. Choosing a complete and balanced diet for the appropriate life stage will provide an adequate amount. Pets that are growing or in a phase of reproduction will have higher arginine requirements than adults.
Deficiencies:
Not receiving enough arginine through the diet can lead to a metabolic condition called hyperammonemia. This condition is characterized by increased levels of ammonia in the body, which can lead to a variety of symptoms, including vomiting, lethargy, and reduced food intake.
Toxicities:
Currently, there is no toxic limit established for arginine. However, excess arginine consumption may lead to impaired growth.
Histidine
Role in the Body:
Histidine is an essential amino acid that has an important structural role in proteins. This amino acid is vital for the body to acquire oxygen, as it plays a special role in oxygen exchange in the lungs and other tissues! Histidine is also converted to histamine, which plays an important role in the immune system.
Nutritional Sources:
Histidine can be found in plant sources such as soybeans, peas, oats, and wheat. It is also present in animal sources such as poultry, fish, eggs, and dairy sources.
Amount Needed:
Histidine is needed in various amounts depending on your pet’s life stage. Choosing a complete and balanced diet for the appropriate life stage will provide an adequate amount. Pets that are growing or in a phase of reproduction will have higher histidine requirements than adults.
Deficiencies:
Insufficient histidine intake can lead to reduced growth, weight loss, and lower food intake.
Toxicities:
Currently, there are no toxic levels reported for histidine in cats or dogs.
Isoleucine
Role in the Body:
Isoleucine is an essential amino acid that has an important structural role in proteins. Isoleucine is ketogenic, meaning it can be converted into acetyl-CoA to provide energy. It is also glucogenic, meaning it can be converted into glucose to provide energy.
Nutritional Sources:
Isoleucine can be found in plant sources such as sunflower seeds, pumpkin seeds, soybeans and peas. It can also be found in animal sources such as beef, pork, chicken, tuna, and dairy.
Amount Needed:
Isoleucine is needed in various amounts depending on your pet’s life stage. Choosing a complete and balanced diet for the appropriate life stage will provide an adequate amount. Pets that are growing or in a phase of reproduction will have higher isoleucine requirements than adults.
Deficiencies:
Not receiving enough isoleucine through the diet can lead to reduced food intake, impaired growth, and weight loss. It can also impair resistance to common bacteria found on the skin, which can lead to eye, nose, mouth, and skin infections.
Toxicities:
Currently, there are no toxic levels reported for isoleucine in cats or dogs.
Leucine
Role in the Body:
Leucine is an essential amino acid with numerous roles in the body. One role of leucine is to assist in protein synthesis in skeletal muscle, and it also helps regulate blood glucose levels.
Nutritional Sources:
Leucine can be found in plant sources such as chickpeas, brown rice, and peanuts. It can also be found in animal sources such as chicken, beef, salmon, cheese, and eggs.
Amount Needed:
Leucine is needed in various amounts depending on your pet’s life stage. Choosing a complete and balanced diet for the appropriate life stage will provide an adequate amount. Pets that are growing or in a phase of reproduction will have higher leucine requirements than adults.
Deficiencies:
Insufficient consumption of leucine can lead to decreased food intake, weight loss, and a negative nitrogen balance. A negative nitrogen balance is when urinary nitrogen losses are greater than oral nitrogen intake.
Toxicities:
Currently, there are no toxic levels reported for leucine in cats or dogs. A high concentration of leucine in the diet may increase food intake.
Lysine
Role in the Body:
Lysine is an essential amino acid vital for your pet’s health. It plays a key role in collagen formation, which supports healthy skin and joints. Additionally, lysine is weakly ketogenic, meaning it can be converted into ketone bodies for energy.
Nutritional Sources:
Lysine can be found in plant sources such as soy, nuts, seeds, and lentils. Lysine can also be found in animal sources such as beef, pork, fish, and eggs.
Amount Needed:
Lysine is needed in various amounts depending on your pet’s life stage. Choosing a complete and balanced diet for the appropriate life stage will provide an adequate amount. Pets that are growing or in a phase of reproduction will have higher lysine requirements than adults.
Deficiencies:
Not receiving enough lysine through the diet can lead to reduced food intake and weight loss.
Toxicities:
Currently, there is no toxic dose reported for lysine in cats. In dogs, excess lysine causes growth depression and an arginine deficiency.
Methionine (and Cysteine)
Role in the Body:
Methionine-Cysteine are two important amino acids that can be found in your pets diet. Methionine is important for a number of normal metabolic processes including cell replication, fat synthesis, and it is a precursor of cysteine. On the other hand, cysteine is used as a precursor for glutathione (an antioxidant), felinine (a compound found in cat urine), and taurine in dogs.
Nutritional Sources:
Methionine-cysteine can be found in protein based ingredients like meats and organs, but can also be found in dairy, cereal grains, and low levels in legumes.
Amount Needed:
Pets who are growing or gestating have a higher methionine-cysteine requirement than those who are adults. Choosing a complete and balanced diet for the appropriate life stage will provide an adequate amount of methionine-cysteine. These life stages include growth, maintenance, and gestation/lactation, and can be found near the ingredient list on the pet food label.
Deficiencies:
Deficiency in methionine-cysteine generally leads to weight loss, lethargy, abnormal skin lesions, including reddening, and swelling that is notably seen on the front foot pads in both cats and dogs.
Toxicities:
In dogs, excessive methionine can lead to neurological symptoms including poor muscle control, disorientation, lethargy, and tremors. In cats, it has been shown that overconsumption of this amino acid can lead to a decrease in weight gain and anemia.
Phenylalanine
Role in the Body:
Phenylalanine is an essential amino acid that plays a crucial role in building proteins, hormones, and neurotransmitters in the body. It’s also vital for producing eumelanin, a pigment responsible for dark colors in hair, skin, and eyes. In black-coated animals, phenylalanine helps create that rich black color by ensuring adequate eumelanin production. Without enough phenylalanine, the coat may lose its vibrant color and turn reddish-brown.
Nutritional Sources:
Phenylalanine can be found in protein-based ingredients such as meat, fish, eggs, dairy products, legumes, and whole grains. These sources help ensure your pet gets the phenylalanine they need for healthy body functions.
Amount Needed:
Phenylalanine is needed in various amounts depending on your pet’s life stage. Choosing a complete and balanced diet for the appropriate life stage will provide an adequate amount. Pets that are growing or in a phase of reproduction will have higher phenylalanine requirements than adults.
Deficiencies:
A deficiency in phenylalanine can lead to reduced food intake, weight loss, and changes in coat color, particularly in black-coated animals, where the fur may turn reddish-brown.
Toxicities:
Currently, there are no toxic levels reported for phenylalanine in cats or dogs.
Threonine
Role in the Body:
Threonine is an essential amino acid that is glucogenic, meaning it can be converted into glucose, a vital energy source for the body. Threonine plays a crucial role in maintaining intestinal health by supporting the structure and function of the intestines, including immune defense, barrier integrity, and healthy microorganisms.
Nutritional Sources:
Threonine can be found in both animal and plant-based foods. Animal sources include beef, lamb, and pork, while plant-based sources include soy products, flaxseeds, wheat germ, and lentils.
Amount Needed:
Threonine is needed in various amounts depending on your pet’s life stage. Choosing a complete and balanced diet for the appropriate life stage will provide an adequate amount. Pets that are growing or in a phase of reproduction will have higher threonine requirements than adults.
Deficiencies:
A deficiency in threonine can lead to reduced food intake and weight loss. In cats, a lack of threonine can cause cerebral dysfunction, leading to symptoms like limb tremors, jerky head movements, and unsteady legs.
Toxicities:
Currently, there are no toxic levels reported for threonine in cats or dogs.
Tryptophan
Role in the Body:
This amino acid is important for protein synthesis and is a precursor for the vitamin niacin and a variety of neurotransmitters. Cats cannot make adequate amounts of niacin from tryptophan alone and require further supplementation in their diet.
Nutritional Sources:
Tryptophan is commonly found in animal products including beef, lamb, pork, poultry, and dairy. It can also be found in whole grains, nuts, seeds, and legumes.
Amount Needed:
Pets who are growing or gestating have a higher tryptophan requirement than those who are adults. Choosing a complete and balanced diet for the appropriate life stage will provide an adequate amount. These life stages include growth, maintenance, and gestation/lactation, and can be found near the ingredient list on the label.
Deficiencies:
Lack of tryptophan in the diet can lead to reduced food intake, appetite loss, weight loss, depression, increased vocalization, and behavioral changes in both cats and dogs.
Toxicities:
Excess tryptophan in cats and dogs results in serotonin syndrome; symptoms include vomiting, high body temperature, rapid heart rate, and seizures.
Valine
Role in the Body:
Valine is a glucogenic amino acid, meaning it serves as a glucose precursor when broken down as an energy source for the body. Currently, valine’s only known role is as a precursor for proteins.
Nutritional Sources:
Valine can mainly be found in animal products (beef, chicken, fish & dairy), with lesser amounts being present in nuts, veggies, and whole grains.
Amount Needed:
Choosing a complete and balanced diet for the appropriate life stage will provide an adequate amount. These life stages include growth, maintenance, and gestation/lactation, and can be found near the ingredient list on the label.
Deficiencies:
Lack of valine in the diets of cats and dogs generally leads to weight loss; no other clinical signs have been reported.
Toxicities:
Currently, no known toxic levels of valine have been reported for cats and dogs.
Taurine
Role in the Body:
Taurine is an essential amino acid for our feline friends, while dogs can make their own from other dietary components. Taurine plays a vital role in many physiological functions. It supports healthy fetal development, growth, and reproduction. Taurine also keeps vision sharp and hearts strong.
Nutritional Sources:
Taurine can mainly be found in animal products such as chicken, turkey, beef, and fish. Dark meat typically contains more taurine than light meat.
Amount Needed:
Taurine is needed in various amounts depending on your pet’s life stage. Choosing a complete and balanced diet for the appropriate life stage will provide an adequate amount.
Deficiencies:
A diet lacking taurine can be harmful to our pets. In dogs, taurine deficiency can lead to a heart condition called dilated cardiomyopathy. For cats, it may cause blindness, heart failure, weakened immune response, abortion, and birth defects.
Toxicities:
Currently, there are no toxic levels reported for taurine in cats or dogs.
Wrapping Up
Protein and amino acids are the foundation of your pet’s health, influencing everything from muscle strength to immune function and even coat color. Understanding their roles helps you make informed choices about your pet’s diet and overall well-being. Remember, a complete and balanced diet formulated for your pet’s life stage is the best way to meet these needs, and your veterinarian is your greatest resource for personalized guidance.
If you have any concerns regarding the protein or amino acid content of your pets’ diet, please consult with your veterinarian.
Written by: Hannah Godfrey, MSc, PhD, Post-Doctoral Fellow with Julia Laboni, Tonia Palermo, and Alison Ng
Reviewed By: Dr. Adronie Verbrugghe, DVM, PhD, Dip ECVCN, Associate Professor and Royal Canin Veterinary Diets Endowed Chair in Canine and Feline Clinical Nutrition