Laura Gaylord, DVM, DACVIM (Nutrition)
Board Certified Veterinary Nutritionist®
Fuquay Varina, NC
No one would dispute that protein is an essential nutrient.
This is true for humans as well as our beloved pets. Protein provides essential amino acids that are key to survival and optimal health. Pet owners are keen to select diets for their dogs and cats that provide “high quality” protein sources, and pet food marketing spends significant time invested in protein messaging for their products. But not all proteins are created equal and protein can directly impact the health of both dogs and cats. As veterinarians, we can recommend diets that provide optimal protein in both quality and quantity that are also appropriate for the life stage and condition of the pet in order to maximally support health.
Proteins are composed of amino acids, 10 of which are considered essential for dogs and 11 for cats.
“Essential” means they must be consumed in the diet and are not made by the body. Some amino acids may also be considered “conditionally essential” if they are additionally required in the diet during times of greater need such as growth, reproduction or illness. Amino acids have numerous important bodily functions as they are critical in the synthesis and repair of cells, tissues and organs, they serve as transport molecules in the blood, as enzymes in the digestive tract, as messenger molecules (or hormones) for the endocrine system and as antibodies in the immune system. They can also serve as an energy source for both cats and dogs. Protein is not stored in the body to the same degree that extra fat is stored in fat mass or carbohydrates are stored as glycogen in muscles or the liver. Rather, structural proteins in all tissues may be considered amino acid stores, but the body will turn to the muscle or liver and also the blood protein albumin for protein/amino acid needs.
When protein intakes are insufficient extensive loss of muscle mass can occur which can ultimately impair muscle function.1 The highest protein requirements will occur during growth, gestation, lactation, increased physical activity/sporting or with working pets, but will also occur in certain disease conditions such as burns, cancer, trauma and cardiac disease.1 Even lacking one essential amino acid will result in the inability to make a necessary protein and the breakdown of body proteins to provide it. This deficiency state can then result in decreased body proteins and muscle atrophy.1
We have guidelines for minimal requirements for amino acids and total protein as well as levels that are recommended allowances and also guidelines for commercial pet foods provided by the National Research Council (NRC) and the Association of American Feed Control Officials (AAFCO).2,3 Minimum requirements, however, may not be the same as OPTIMAL intakes for any particular pet given its individual circumstances. In addition, newer research has indicated that minimum requirements previously determined may not be sufficient for all breeds or sizes of dogs.4-7
Sources of proteins in pet foods include animal-derived ingredients.
Sources of proteins in pet foods include animal-derived ingredients such as muscle meats, organs, tissues, meals and by-products while plant-based ingredients include cereal glutens, corn, legumes and other plant protein isolates or concentrates. Proteins of “high biological value” are those with very good digestibility that contain a high quantity of essential amino acids.1 Animal proteins have a higher biological value while plant-based proteins have overall a lower one. Plant-based proteins may also contain higher quantities of non-essential amino acids as well as additional fibers, so called “anti-nutrients”,that may interfere with the digestion and absorption of other nutrients.8-10
Passionate marketing has described dogs as wolves or implied that they are “true carnivores” similar to cats.
Despite classification as a member of the Carnivora family, dogs are more appropriately described as omnivores as they can and will feed on both animal and vegetable matter in their diet. Dogs have evolved adaptations during domestication to facilitate this capacity. They are, however, best described as a “carnivorous omnivore” as natural feeding studies indicate that dogs do prefer to consume a diet containing 30% of energy from protein with less than 10% of energy derived from carbohydrates.11 Similar natural feeding studies indicate that cats prefer a diet composed of 52% of calories from protein with 12% from carbohydrates.12 Obligate carnivores such as cats continuously utilize protein for glucose production (termed gluconeogenesis) and do not downregulate enzymes in this pathway even during times of protein insufficiency. Adult cats require 2-3x more protein in their diets compared to other omnivorous species and kittens require 1.5x more protein than the young of other species.13 Considering protein quality and quantity in the diet is thus essential for both dogs and cats to optimally support their health.
Protein quality in commercial diets is unfortunately very difficult to assess for both pet owners and veterinarians.
Pet food labeling can be manipulative and deceptive, or simply not revealing as it relates to the quality of the food or its ingredients. While labels must meet regulatory guidelines, pet food labels generally fail miserably at providing the information that every pet owner and veterinarian is actually looking for: is this the best food to feed to my pet (or patient)? Often pet owners are seeking diets that list animal proteins first in the ingredient list as they are perceived as the best, most nutritious ingredient. The pet food label lists ingredients as defined by the Association of American Feed Control Officials (AAFCO) in descending order by weight as is required by the U.S. Food and Drug Administration (FDA). This means the heaviest ingredients are listed first, but this does not mean the first ingredient is contributing the most nutrition.
The ingredient list does not provide any information on the quality or digestibility of the ingredients included or whether they are used in amounts that provide any sort of nutritional benefit. For example, ingredients that appeal to pet owners like blueberries and spinach probably provide little nutritional benefit in the food as they are used in a relatively small quantity, whereas poultry by-product sounds less appealing but provides the actual essential nutrients. This also could facilitate deceptive marketing where more desirable animal-based ingredients are listed first as they are heavier due to included water weight, while less desirable plant-based ingredients are then listed further down the ingredient list when in actuality they are contributing more nutrients in the food. More transparency certainly is needed in pet food labeling, nutrition information and nutrient quality related to ingredients in pet foods.
Protein is a nutrient that may help facilitate weight management.
Unfortunately, at this time a majority of our pets are overweight or obese.14 Obesity is associated with a higher risk of many disease conditions including joint/mobility disorders, diabetes, endocrine disease, respiratory disease, cardiovascular disease, liver dysfunction, and urinary tract disease.14,15 Ultimately, obesity may cause reduced quality of life and a shortened life span. Obesity may also result in great emotional and financial burdens for pet parents.14 Choosing diets that are higher in protein may encourage satiety and suppress appetite thereby reducing food intake while also promoting a greater caloric expenditure at rest (thermic effect of the food).16-18 Diets higher in protein may make weight control easier and spare muscle mass loss during weight loss.19,20 After weight loss, higher protein diets may help maintain an appropriate weight.21 Higher protein diets may also facilitate a “soft weight loss” plan where minimal effort is required to move the slightly overweight pet towards a more optimal body weight and body condition.22
Spaying and neutering is a critical time that changes the body in many ways, both hormonally and metabolically.
This is also a key time for diet interventions. While spaying and neutering is advocated for virtually all dogs and cats, this intervention does have consequences. It is, in fact, the largest risk factor for overweight/obesity later in life for our pets.23,24 With this procedure, there is a decrease in metabolic rate and an increase in desire for food intake.25-27 The removal of sex hormones results in an increased appetite, up to 63% in dogs and 23% in cats.28,29 Unfortunately, this change starts immediately following the procedure.30 If no changes in diet are instituted, weight gain is likely. As veterinarians, we can no longer fail to address this concern at the time of the spay/neuter procedure and we must proactively discuss weight management, appropriate diets and feeding amounts with our pet parents. Choosing diets that help control appetite and those that promote satiety (a sense of fullness) containing proteins of high biologic value will help manage weight and/or prevent weight gain associated with spay/neuter.16
Protein is a key nutrient needed for maintenance of optimal muscle mass.
A pet’s mobility relies on maintaining muscle, and muscle makes up the supportive structures of the joint itself. Muscle wasting is common in our older pets.31,32 Maintaining an ideal body weight with adequate muscle mass into the later years can help ensure continued mobility and quality of life. Providing diets with optimal protein quality and quantity ensures adequate amino acids are present and utilized to maintain muscle mass synthesis.
Protein may also impact other body systems including the skin and coat, immune system, urinary tract, and the kidneys.
Proteins make up 65-95% of the hair structure in dogs and cats. As much as 30% of daily protein intake may be used for skin and coat renewal in small breed dogs with long haircoats.1 Keratin production, coat color, and skin immune function rely on adequate protein intake.1 Proteins provide the majority of essential building blocks for cell synthesis in the immune system, and protein deficiency will result in a potentially weakened immune response. A mild protein deficiency with older pets may result in impaired immune function and compromised gut barrier function.33,34 Higher protein diets may promote water intake, produce a more dilute urine and result in a more acidic urinary pH.35,36,37-39 These features may be beneficial for maintaining a healthy urinary tract.
Many pet owners inquire if higher protein diets are harmful especially related to kidney function.
Studies in humans have demonstrated that higher protein diets may increase glomerular filtration within the kidney, however, this is a normal adaptive response and there is no association with a deterioration of kidney function in normal, healthy subjects.40,41 To date there are no studies demonstrating that high protein levels cause kidney disease development. Both short term and long term studies in healthy dogs and cats were unable to demonstrate adverse effects from increased dietary protein intakes.42 33,43,44
In summary, providing high quality protein at an optimal level in our patients’ diets can optimize their health by ensuring adequate protein for essential functions is present.
Higher protein levels may provide the additional benefit of proactively managing appetite and body weight. This benefit is particularly appealing as most of our veterinary patients are spayed and neutered which increases risk of overweight and obesity and also increases the risk of disease conditions that impact quality of life and ultimately result in a shortened life span.
Board Certified Veterinary Nutritionist is a registered trademark of the American College of Veterinary Nutritionists.