Nutritional Myths
Owners are sometimes confused or misinformed about nutritional facts pertaining to pet foods, and three common nutritional myths have been propagated in the popular press. The first myth is that meat by-products are of inferior quality compared to whole meat. The second myth is that feeding trials are unnecessary, and the third myth is that pet food preservatives are bad. This paper examines the known facts related to these three myths and discusses the importance of food trials and the different classes and forms of antioxidants used in pet foods.
Introduction
With the widespread availability of the Internet, clients have an even greater access to information than ever before. Where previously they had relied on information from friends, breeders, and news sources, they now have the entire Internet as a potential source of information. Unfortunately, many owners do not filter the information they receive, do not closely examine the source of the information or evaluate its references, and they sometimes take everything in their sources as gospel. Many clients feel uncomfortable talking to their veterinarian about nutrition questions, or they feel that they know as much as the veterinarian does. Obtaining information from nonprofessional or unsubstantiated sources has caused many well-intentioned clients to follow poor recommendations. The purposes of this paper are to describe some of the more common nutritional myths that clients may believe, and to examine the factual information available pertaining to each myth.
Meat By-Products
One important myth is that meat by-products are inferior in quality compared to whole meat in a diet. When listed on an ingredient label, meat is defined by the Association of American Feed Control Officials (AAFCO) as any combination of skeletal, striated muscle or muscle found in the tongue, diaphragm, heart, and esophagus, with or without the overlying fat and the portions of the skin, sinew, nerves, and blood vessels that normally accompany the muscle.1 Meat may be derived from parts of whole carcasses [Figure 1]. It must be suitable for use in animal foods, so it would exclude feathers, the head, feet, and entrails.1 Meat by-products are defined as nonrendered, clean parts of the carcass and may contain lungs, spleen, kidneys, brain, liver, blood, bone, the head, feet (of poultry), partially defatted fatty tissue, and stomach and intestines emptied of their contents.1 Meat byproducts do not include hair, horns, teeth, or hooves.1
Depending on the supplier and the type of refining process that the manufacturer uses, by-products can vary greatly in the amount of nondigestible material they contain. The ash content provides some information as to the quality of the by-products being used. High ash content is an indicator of a poor-quality protein, with lower digestibility.2 The presence of by-products does not indicate a poor-quality diet, but a higher ash-to-protein ratio does.2 Feeding trials evaluate digestibility and nutrient content of the ingredients. The results of feeding trials are available in most product reference guides, in on-line references, and can be obtained by contacting the manufacturer.
Feeding Trials
Another myth that has circulated among owners is that feeding trials are unnecessary. Feeding trial protocols established by AAFCO for adult maintenance foods last 6 months, require only eight animals per group, and monitor a limited number of parameters.3 Parameters that are evaluated include the minimum daily nutrient requirements as defined by the National Research Council (NRC).3,4 Minimum requirements are the minimum levels of nutrients that are sufficient over time to maintain the desired physiological functions of the animals in the study population.3 The recommended daily intake is the level of intake of a nutrient that appears to be adequate to meet known nutritional needs of most healthy individuals [Figure 2].3
The NRC recommendations serve as a guide to formulating diets, but they do not account for digestibility or nutrient availability. Feeding trials that meet AAFCO guidelines provide reasonable assurance of nutrient availability and sufficient palatability to ensure acceptability. They also provide some assurance that the product supports certain functions such as gestation, lactation, and growth.3 A feeding trial is currently the only way to accurately assess the quality of the protein in a diet, because feeding trials determine digestibility of a protein in vivo, which inherently affects its quality.
Passing a feeding trial does not ensure that the food is effective in preventing long-term nutritional or health problems, however. Feeding trials may not detect problems that have a low prevalence in the general population. A feeding trial is also not designed to ensure optimal growth or maximize physical activity. If a diet has not been subjected to a feeding trial by the manufacturer, then, in essence, the clients will be conducting the feeding trial using their own pets.
Although feeding trials (especially those of therapeutic diets) cannot be expected to detect all nutritional deficiencies or excesses (especially those associated with malabsorption or maldigestion), they do provide valuable information. Feeding trials are conducted on healthy dogs and cats and include control animals that are of the same breed and gender. During the feeding trial, the animals must receive the test food as their only source of nutrition. The same dietary formula must be fed throughout the entire trial. The trials are conducted by measuring the daily food consumption and weekly body weights of the animals. Certain laboratory parameters are measured at the end of the trial, and complete physical examinations are performed by a veterinarian at the beginning and end of the trial. The maximum number of animals that are removed from the study for nonnutritional reasons or because of poor food intake cannot exceed 25%.3 Necropsies are conducted on any animals that die during the trial.
Additional information is recorded on reproducing animals, such as body weight within 24 hours of delivery, the offspring’s body weight within 24 hours of birth, litter size at birth, litter size 1 day later, and litter size at the end of the study.3,4 Any stillborn offspring or congenital abnormalities are also recorded.3,4 At the end of the feeding trial, the results are compared to those obtained from a control group of animals, from a historical colony average, or from reference values published by the AAFCO.3,4
All reliable manufacturers of dog food conduct feeding trials on their foods and continue to conduct them as the foods are changed and updated for palatability and as new evidence is discovered regarding nutritional requirements. To verify if feeding trials have been conducted on a food, check the product label to find the source of AAFCO certification. If feeding trials have been done, the label will indicate such.
Pet Food Preservatives
A third common nutritional myth is that pet food preservatives are bad. Preservatives are defined as any substance capable of inhibiting or retarding the growth of microorganisms or of masking the evidence of such deterioration.1,4 The primary nutrient requiring protection through preservatives during storage is dietary fat. Fats can be in the form of vegetable oils, animal fats, or the fat-soluble vitamins A, D, E, and K. These nutrients may undergo oxidative destruction, called lipid peroxidation, during storage.4
Antioxidants are included in foods to prevent lipid peroxidation.1,4 Oxidation of fats in pet foods also results in loss of caloric content and the formation of toxic forms of peroxides that can be harmful. The Food and Drug Administration (FDA) defines an antioxidant as any substance that aids in the preservation of foods by retarding deterioration, rancidity, or discoloration as the result of oxidation processes.1,4 Various types of antioxidants have been accepted for use in human and animal foods since 1947.4 Antioxidants do not reverse the oxidative effects on foods once they have started, but rather retard the oxidative process and prevent destruction of the fats in the food. For antioxidants to be fully effective, they must be included in the food when it is initially mixed and processed. The timing of antioxidant inclusion in the food helps to prevent rancidity; to maintain the food’s flavor, odor, and texture; and to prevent accumulation of the toxic end-products of lipid degradation.1,4
Nature-Derived Antioxidants
Antioxidants can be divided into two basic types: nature-derived products and synthetic products. Nature-derived products are commonly found in certain grains, vegetable oils, and in some herbs and spices.4 All of these natural compounds are processed in some way to make them available for use in commercial foods. The most common nature-derived antioxidants are the mixed tocopherols (i.e., vitamin E compounds), ascorbic acid (i.e., vitamin C), rosemary extract, and citric acid.1,4
Alpha tocopherol has the strongest biological function in tissues, but it is a poor antioxidant in foods.4 Delta and gamma tocopherols both have low biological activity but are more effective than alpha tocopherol as antioxidants.4 Tocopherols used in foods are obtained primarily from distillation of soybean oil residue. Tocopherols rapidly decompose as they protect the fat from oxidation, and for this reason foods preserved with mixed tocopherols have a shorter shelf life than foods preserved with a mixture of several types of antioxidants.4
Ascorbic acid (vitamin C) is a water-soluble antioxidant and is not readily miscible with the fatty portion of foods. Ascorbic acid works synergistically with other antioxidants, such as vitamin E and butylated hydroxytoluene.4 Ascorbyl palminate is similar in structure to ascorbic acid, but it is not normally found in nature. When hydrolyzed, ascorbyl palminate yields ascorbic acid and the free fatty acid, palmitic acid, both of which are natural compounds.1
Rosemary extract is obtained from the dried leaves of the evergreen shrub, Rosemarinus officinalis. It is effective as a natural-derived preservative in high-fat diets, and it has been shown to enhance antioxidant efficiency when combined with mixed tocopherols, ascorbic acid, and citric acid.4 Much processing of the plant oil is needed before its addition to foods, because the oil may affect the taste of the food.1 Citric acid is found in citrus fruits such as oranges and lemons, and it is often combined with other nature-derived antioxidants.4
Because of the high cost of using nature-derived antioxidant compounds, they are usually used in conjunction with synthetic antioxidants in pet foods. It is difficult to attain the necessary level of nature-derived antioxidants without the cost becoming prohibitive.4
Synthetic Antioxidants
Synthetic antioxidants include butylated hydroxyanisole, butylated hydroxytoluene, tertiary butylhydroquine, and ethoxyquin. Butylated hydroxyanisole and butylated hydroxytoluene are approved for use in both human and animal foods, and they have a synergistic antioxidant effect when used together. Both butylated hydroxyanisole and butylated hydroxytoluene are highly efficient in protecting animal fats, but they are slightly less effective when used with vegetable oils. Tertiary butylhydroquine is an effective antioxidant for most fats, and it is approved for use in human and animal foods in the United States. It is not approved for use in Canada, Japan, or the European Economic Community, so it is not usually used in pet foods intended for sale in the international market. Ethoxyquin has been approved for use in animal foods for >30 years, and it has been used in pet food manufacturing for >15 years.1,4 Ethoxyquin is more efficient as an antioxidant than either butylated hydroxyanisole or butylated hydroxytoluene, so lower levels of ethoxyquin can be used.4 It is especially effective in the protection of oils that contain high levels of polyunsaturated fatty acids.1,4
If clients are concerned about the use of synthetic antioxidants in pet foods, they should realize that most canned foods do not contain antioxidants and that many commercially prepared dry foods use nature-derived antioxidants.1,4 In addition, no studies have been published that support the contention that synthetic antioxidants (in general) or ethoxyquin (in particular) are responsible for the variety of health problems reported by owners to the FDA. The proper use of antioxidants prevents the occurrence of rancidity and the production of toxic peroxide compounds in foods.
Synthetic antioxidants are more effective than natural antioxidants, and they better withstand the heat, pressure, and moisture applied during food processing. They are also better at preserving the fat-soluble vitamins A, D, and E.1,4 In most cases, synthetic antioxidants are the best class of antioxidants to use because of their efficacy, efficiency, and low cost. In contrast, the nature-derived antioxidants are unstable, and high levels are needed for effective protection. These factors make nature-derived antioxidants difficult to use as the sole preservative in pet foods.1,4
Conclusion
It is important to educate clients about the facts surrounding nutritional myths. With proper information, clients are able to choose a pet food that contains high-quality ingredients and one that has undergone feeding trials and is properly preserved so that all the ingredients are available to the pet.
Citation: Journal of the American Animal Hospital Association 41, 4; 10.5326/0410273
Citation: Journal of the American Animal Hospital Association 41, 4; 10.5326/0410273
When clients think of “meat” in pet foods, this is what they have in mind.
Many clients feel that “feeding trials” are experiments on animals and are not justified. Feeding trials are allowing animals to do what they do normally (eat) under controlled conditions with medical supervision.
