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• Nutrition 101

Understanding Dog and Cat Nutrition

By Dr. Karen Shaw Becker, DVM, NMD

Protein

Protein is an integral part of every living cell in our pet’s body. Next to water, protein makes up the majority of our pet’s body weight. Proteins are the foundation of a carnivorous diet. They are necessary for the formation of healthy cells, enzymes, hormones, a variety of body secretions, ligaments, tendons, organs and protective tissues.

The quality and quantity of protein is very important for dogs and cats. The protein pets eat is broken down into amino acids, which the body absorbs and chains together to form the specific proteins it needs. Amino acids are chemical units, or the building blocks, that make up proteins. The body can manufacture some of the 28 amino acids needed but others must be provided in the diet (essential amino acids).

Unfortunately, quality and digestibility of protein included in pet foods is not addressed by AAFCO. Feathers are 100% protein (and 100% indigestible) and could theoretically be used as a protein source. Because AAFCO does not require manufacturers to list what type of protein makes up “crude protein,” pets may be consuming too much indigestible, poor quality protein, which leads to a strain on the kidneys.

Commonly, veterinarians recommend reducing the amount of protein a pet consumes as it ages. However, research has shown that geriatric and young dogs have the same efficiency in digesting and metabolizing nutrient intake(1). In fact, research shows that, “Benefits from a reduced protein diet typical of existing canine geriatric products have never been proven, and the possibility exists that a reduced protein diet is not in the best interest of the geriatric patient(2).” Switching to a “senior” diet with reduced or restricted protein levels is not only unwarranted but potentially hazardous to your pet’s health.

Taurine, an essential amino acid, must be supplied to cats. Taurine naturally occurs in raw meat but is degraded when the protein is denatured at high temperatures. Many cat foods have added taurine to help prevent cats from developing cardiomyopathy and retinal atrophy. Doesn’t it make more sense to simply feed cats the correct diet in the correct, unadulterated form? Many vets recommend a high fiber diet for cats with obesity, diabetes or chronic GI issues. As the fiber content in the diet increases, fecal taurine losses also increase, however, many commercial prescription diets do not account for this loss.

Fat

Dogs and cats burn fat much better as an energy source than we do; in fact fat yields 2.25 times more energy than carbs or proteins. Although most commercial diets only contain 5-15% fat, dogs and cats can do well with a diet that contains 25-50% fat as long as they are active (Morris et al). Most of the fats found in dog foods are poor quality and loaded with preservatives, which makes them unhealthy. The term “low fat” has become so instilled in Americans that the trend is carrying over to our pet population. Dogs and cats need fats. However, a high fat content in foods means a much shorter shelf life. If the body is unhealthy and cannot process fat, fat will be passed in the stool and the body will become deficient in fat-soluble vitamins A, D, E, K and several minerals.

Unsaturated fatty acids are oils that are also necessary for dogs and cats. Linoleic acid (omega 6) is an essential fatty acid required by all animals. It is the main unsaturated fatty acid in most vegetables and makes up 15-25% of most poultry fat. Cats require arachidonic acid, which only comes from animal sources. Essential fatty acids are necessary for a whole host of body functions, including successful reproduction, normal cell membrane synthesis, normal healing and normal skin and coat.

Fatty acids are very sensitive to heat and are inactivated above 150 degrees. At high temperatures these oils oxidize and become rancid which causes free radical formation and cell death. All pet foods that are cooked at high temperatures contain these unhealthy oxidized oils, called trans-fats. Most pets maintained on commercial diets without fatty acid supplementation eventually show signs of deficiency, including persistent pyoderma (skin infections), alopecia (hair loss), excessive shedding, “hot spots,” brittle hair and flaky skin.

Carbohydrates (grains) and Fiber

Dogs and cats do not have a carbohydrate requirement. Small Animal Clinical Nutrition (Morris et al) states that, “Dietary soluble carbohydrate requirements have not been established for the dog and cat and insoluble carbohydrates provide no significant amount of energy to the dog and cat. In fact, they reduce the energy density of the diet by displacing protein and fat.” (pg 11). An abundance of insoluble carbohydrates (fiber) in most commercial foods has also led to reduced absorption of vital nutrients. Soluble carbohydrates are the main component of most processed foods.

Kibbled food must contain grain to be cost effective. Some grains are more absorbable than others. For instance, carnivores cannot utilize soy very efficiently. The higher quality kibbles contain whole grains, such as whole barley or millet, whereas the cheaper foods contain grain fractions, such as wheat flour or middlings. Some grains are more reactive, immunologically, than others. Corn and wheat cause more adverse reactions than other types of grains.

The term “fiber” refers to the tough plant cell walls that are resistant to digestion by mammalian GI tracts. Predators rely on the small amount of fur their prey provides for the roughage needed for normal bowel health. Although there is not a physiologic requirement for additional fiber in our pet foods, almost all commercial foods include it as a filler. Quality pet food manufacturers rely on whole grains (such as whole barley or whole millet) and whole vegetables to provide the roughage our pets need. The cheaper pet foods contain less desirable fiber sources such as beet pulp, peanut shells and other grain hulls, guar gum and cellulose (wood fiber).

Fiber can be categorized as soluble/insoluble and fermentable/nonfermentable. Soluble fiber can be dissolved in water, insoluble fiber cannot. Fermentable fiber (i.e. yucca and chicory) can be utilized by the bacteria within the GI tract to yield short-chain fatty acids. These fatty acids keep the colon acidic and the lining of the GI tract healthy.

Fiber is added to pet foods in large quantities for several reasons. Fiber has a stool normalizing effect but is also inexpensive. Obviously, minimal GI disturbances are necessary if customers are going to re-purchase a food. Fiber is used to artificially firm the stool and can also prevent constipation. Sounds perfect, but too much fiber can also be detrimental. High fiber diets speed small intestine transit time, reducing nutrient absorption. There is also a physical blockage of nutrients due to the fiber impairing the contact of absorbable amino acids to the intestinal wall. Fiber also absorbs significant amounts of water. The excessive fiber load causes retention of the stool in the colon, where water is naturally reabsorbed from the feces. Anaerobic bacteria can over proliferate in the colon, causing gas and absorption of toxins that should have been expelled.

High fiber diets, or “light” foods, are also used commercially as weight management tools. There has been concern regarding the long-term effects of these diets, which supply up to 10 times the amount of fiber needed by dogs and cats. Over time, impaired absorption of critical nutrients could lead to chronic nutritional impairments(3). Morris documents that commercial diets for carnivores contain 2-4 times the fiber content of typical human diets. Recent studies have also documented that high fiber diets have no effect on a dog’s appetite. Some researchers believe the weight loss occurs on these diets because the food is unappealing and pets eat less. Regular commercial pet foods should not contain more than 4% fiber for health.

Fat Fido

Some animals can consume grains and appear to stay healthy. If your dog has trouble maintaining weight, adding carbohydrates is one option that helps the body store fat. However, the average pet does not require the addition of grains to the diet for health. Remember, if your pets do not burn carbohydrates, the body stores them as fat. Most commercial foods are grain (carbohydrate) based, thus, a diet of these foods results in carbo-loading. If your pet is a triathaloner (or equivalent) with no skin/allergy problems then grains may be added to the diet in small quantities (15-20%).

Other Essential Requirements: Digestive enzymes

Next time you watch a nature show on TV about wolves watch closely when the pack makes a kill. Sometimes the announcer even talks about how only the alpha wolf has first dibs on the choicest meats. What do the alpha’s eat first? The GI tract. Why? He needs those rabbits’ digestive enzymes to help him process his food. The carnivorous pancreas cannot secrete all of the enzymes necessary for proper digestion. For thousands of years dogs and cats have relied on enzymes already found in their food to provide part of their digestive enzyme requirement. Enzymes in preys’ GI tracts provide the perfect required enzyme addition for proper digestion. Unfortunately, enzymes are inactivated above 120 degrees making all processed foods devoid of enzymes due to high cooking temperatures. Even most raw food diets are missing some enzymes, as most people do not provide entrails as a part of the diet.

The pancreas supplies 3 main enzymes but the body requires several more for correct digestion. Interestingly, dogs and cats also require maltase and lactase, which are not secreted. The intestinal cells of healthy animals secrete these enzymes. If animals acquire enteritis or another GI inflammatory process, then they cannot fully process carbohydrates and fermentation takes place. This leads to an overgrowth of bacteria and an exacerbation of inflammation and diarrhea.