Protein: The Myths and the Reality

	Dietary protein is necessary for the growth and maintenance of almost all tissues of the body, including muscle, hair, bone and organs.

Protein is found in every living thing and is an essential component of all body tissues. In the body of the dog and cat, over half the dry matter is protein. Dietary protein is necessary for the growth and maintenance of almost all tissues of the body, including muscle, hair, bone and organs. Protein not used for these functions can be utilized for energy.

Is there an ideal source of protein? Is the promise of "no soy" in a pet food an assurance of high quality protein? Will high levels of protein in a pet food cause health problems? Sweep away the myths and the facts about protein may surprise you.

Many pet owners are surprised to discover that protein, in itself, is not required by dogs and cats. They require the proper balance of specific amino acids, the substances which make up protein. Dietary protein comes from many sources of both plant and animal origin. On the following page, Defining Protein gives more information about amino acids.

No one source of protein is perfect. Each is deficient in one or more amino acids. Consequently, amino acid deficiencies and excesses must be balanced when selecting protein sources. For example, soybean meal and corn gluten meal compliment each other perfectly. The amino acids which are deficient in one are present in the other. This comparison is also true of meat and soybean meal. Neither is an ideal protein, but either can be adequate if fed in combination with another source of amino acids.

Dispelling Myths About Protein and Soy

Myths about soybean meal in pet foods have concerned some pet owners. Dispelling these myths should provide the information to help pet owners make an informed decision about the pet food that is most appropriate for their pet.

Myth #1: Animal protein is superior.

The Facts: Not necessarily. The quality of protein in a pet food is determined by the balance of available amino acids. Soy is an excellent source of most amino acids. Used in a diet with complimentary proteins, it can produce high quality dietary protein. Because animal source proteins can vary widely in amino acid content and availability, they can vary in quality.

The protein digestibility of a pet food (the percentage of protein absorbed by the dog or cat) varies according to the quality of the protein source used in the pet food. Poor quality meat or poultry meals are substantially less digestible than soybean meal.

The only assurance of digestibility in a pet food is to be certain that the product has undergone controlled feeding studies. For information about feeding studies for a particular pet food, contact the manufacturer.

Myth # 2:Soy causes loose stools.

The Facts: Small firm stools are not a direct measure of the digestibility of a pet food, although the physical nature of the diet and the type and level of fiber in the diet may influence stool size.

Properly cooked and processed pet foods containing soy may be highly digestible and produce firm stools.

Puppies and kittens frequently have loose stools for many reasons. No cause and effect with a high-quality puppy or kitten food containing soy has been established.

Other factors related to diet that may cause loose stools include:

Sudden diet changes.

Consuming spoiled food from the garbage.

Eating very rich or spicy foods.

Lactose intolerance or other food allergies not relating to soy.

When a product containing soy is fed, it may be considered the cause of loose stools without taking into account other dietary factors.

Myth #3: Soy causes gastric dilatation volvulus (bloat).

The Facts: Soy has been implicated because of its potential for flatulence (gas production) in some dogs. However, the gas associated with bloat has been shown to be swallowed air.

The February 1991 Cornell University College of Veterinary Medicine Animal Health Newsletter addresses the issue of diet and bloat, “There has been considerable controversy over the association of dietary components, such as soybeans or other cereals, with bloat. But there is no evidence that either soybean meal or any dry expanded dog food contributes to bloat.”

Myth #4: Soy causes skin allergies.

The Facts: The ingredient to which the dog is allergic must be identified. Food allergies are quite rare, but may occur to any protein. A dietary trial, under the supervision of a veterinarian, is the only way to be certain that diet is the cause of the allergy and to identify the ingredient to which the dog is allergic.

Not all allergies that affect dogs are food allergies. The kind of allergy should be diagnosed by a veterinarian. Common allergies are:

Flea allergy dermatitis that occurs when the dog is exposed to flea saliva as the flea bites. In addition to fleas, some pets become allergic to other parasites.

Allergic inhalant dermatitis resulting from the inhalation of allergens such as pollen from trees, ragweed, grass and other plants, house dust and mold.

Contact dermatitis caused by a dog’s physical contact with an offending irritant.

Myth #5: Soybean meal depletes the body of its zinc stores.

The Facts: This myth is based on the presence of phytate in soybean meal. In the presence of excess calcium, phytate binds zinc and limits its availability to the pet. Phytate occurs in most plant products. Although phytate renders the zinc in plant products poorly available, it has no effect on the zinc that is already in the body. There is no truth to the myth that soybean meal “eats” or depletes the body of its zinc stores. Good quality nutritionally complete and balanced soy-based diets include adequate available zinc and they are not excessive in calcium.

The Benefits of Soy

In addition to providing high levels of most essential amino acids, soy-based products can help reduce serum cholesterol.

Puppies also have increased requirements for proteins and other nutrients, which must be properly balanced in relation to one another.

Nutrition research also reveals that soy contains a group of chemicals called isoflavones which are related to anti-cancer activity. They are antioxidants which protect cells from damage by oxygen. Oxidation causes changes that are thought to lead to cancer and other diseases.

Unless a pet has a flatulence problem which can be identified by the use of soy, high quality pet food products containing soybean meal can be fed with confidence.

Defining Protein

Protein, in itself, is not required by dogs and cats. They require the proper balance of amino acids, the substances which make up protein. Each protein molecule is made up of hundreds of amino acids combined with one another.

The amino acids, over 20 in number, are often described as "the building blocks of protein." Their
arrangement determines the nature of the protein. Once consumed, dietary proteins in the foods are broken down into component amino acids by digestion. They are then absorbed and distributed by the bloodstream to the body cells which rebuild these amino acids into body proteins.

Certain amino acids can be manufactured by the pet’s body to satisfy its needs. They are described as nonessential amino acids. Others cannot be formed fast enough or at adequate levels to supply the pet’s
needs. They are termed essential amino acids and must be present in the diet of the dog and cat. The absence or deficiency of even one essential amino acid will influence the utilization of all others.

There is little, if any, storage of amino acids in the dog or cat’s body. They are constantly metabolized by the body to build and maintain body tissue. Consequently, protein containing the proper amino acid balance
should be supplied daily.

Ten amino acids considered essential to both the dog and cat are histidine, isoleucine, leucine, arginine,
methionine, phenylalanine, threonine, tryptophan, valine and lysine.

A Cat’s Special Amino Acid Requirement

The cat requires a sufficient level of the amino acid taurine in its diet. All animals, as well as humans, need
taurine, but the cat is the only known mammal which cannot manufacture enough taurine to meet its meta-bolic needs. A taurine deficiency in the cat’s diet can result in degeneration of the retina and, ultimately,
blindness. A taurine shortage can also contribute to cardiomyopathy in certain cats. An appropriate level
of taurine is contained in high quality nutritionally complete and balanced cat foods.

Exceeding Minimum Protein Requirements

The minimum level of protein is required to be stated as part of the guaranteed analysis on all pet food packages. The reason the word "crude" appears in association with the protein content is that the
amount shown is based on laboratory analysis of the nitrogen content from which the protein is estimated. Protein contains 16 percent nitrogen on average.

Many commercial pet foods exceed the minimum requirements which nutrition research has established for protein and other nutrients. This is done because:

.higher levels of protein provide an additional source of amino acids for use under stress conditions such as disease, wound healing and lactation;

some dogs may have nutritional needs that exceed those of average dogs;

nutrient requirements vary with the age, breed, temperament and activity level of the dog as well as environmental conditions;

.highly nutritious pet foods help make up for "junk food" such as table scraps that are a part of many pets’ diets.

Considerable research has been conducted to detect any adverse effects associated with feeding high levels of dietary protein. There is no evidence that the protein levels in a nutritionally complete and balanced pet food cause any health problems in healthy dogs or cats. The protein that is not used for building and
repairing tissue is utilized as energy. The excess nitrogen in the protein is excreted in the urine.

Determining a Dog’s Protein Requirements

A dog’s protein requirements depend upon the life stage and activity of the dog. In normal dogs, the dietary protein requirement is highest for growth, gestation and lactation. During stress the protein requirements are increased. A dog food containing more than 1600 calories and at least 21 percent protein (dry type
dog food) is recommended for reproduction.

The protein requirement for the normal adult dog is not as great. Generally diets designed for maintenance are lower in protein than those for growth.

The hardworking dog requires a diet with higher levels of calories and fat. Normally as the calorie level of a diet increases, the protein content is also increased.

Weight-maintenance diets formulated for sedentary dogs are lower in fat and calories. A dog food formulated for weight maintenance is not appropriate for growing puppies or for pregnant or nursing females.

Puppies, Protein and the Large Breed Myth

Puppies also have increased requirements for proteins and other nutrients, which must be properly balanced in relation to one another. They should receive at least 22 percent of their calories from protein, which translates to between 21 and 30 percent of the diet as protein, depending on the calorie content of the food.

Some concern has been raised regarding the link between protein and developmental bone problems in large breed puppies. According to research conducted at Utrecht University in the Netherlands, dietary protein does not contribute to these problems. In this study, there were no detrimental effects from protein levels up to 32 percent of the diet, but puppies fed with only 15 percent protein showed evidence of inadequate protein intake.

Dispelling Myths About Protein and the Aging Dog

Because older dogs can become less efficient in metabolizing protein than young dogs they require more protein. This need for more protein in the healthy aging dog’s diet contradicts a belief held by some dog owners that older dogs should be fed less protein than young dogs. Perhaps this belief resulted from the myth that associates protein with kidney failure. Once kidney failure is in advanced stages protein restriction is recommended to help alleviate some of the problems associated with this condition.

Research from several leading veterinary colleges shows there is no evidence to indicate that protein at an appropriate level for a nutritionally complete and balanced diet causes kidney damage in dogs.

Two recently completed studies at different universities studied older dogs that had one kidney removed. In each case, half the dogs were fed a high protein diet while the others received diets with restricted protein levels. After four years, the geriatric dogs fed the higher protein diets were as healthy, if not healthier than
dogs fed the lower protein diets.

In addition, early findings from ongoing research at the Purina Pet Care Center, in collaboration with leading veterinary nephrologists, indicates that 45 percent protein has no detrimental effect on the health and kidney function of healthy aging dogs.