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Feeding The Geriatric Pet And Preventing Cancer

Factors Insuring a Long And Happy Life

Pet dogs and cats live considerably longer today than in the past. Better care, especially medical care, is assumed to increase their life expectancy. Life expectancy is also genetically determined. Life span is unique for each animal species and for breeds within a species. Life spans vary greatly for canine breeds. Small breeds and very large breeds of dogs do not live as long as intermediate size breeds. Environmental factors also influence life span of dogs and cats. They include airborne toxins, and toxic-contaminants in food and water. Toxic substances can reduce resistance to disease and directly injure tissues. The greatest exposure to toxic substances is through what is consumed. An animal can eat literally hundreds of pounds of foodstuffs yearly. When commercial pet food is consumed many different chemicals are ingested. Gastrointestinal mucosa contains a single cell layer that protects against entry by noxious substances. No other tissue is such a fragile protective barrier to the outside. The lining of the lungs may be an exception with their exposure to many air pollutants, but they do not contact the vast amount of foreign material that passes through the digestive tract. If toxins are important in promoting aging, most will enter the body through the digestive tract. Thus, a high quality diet is important in supporting long life expectancy in dogs and cats.

Feeding Aged Pets

Manufacturers design some pet foods for aged dogs. Compared to diets for younger dogs, these have reduced fat and possibly increased fiber. Fat content is less because obesity is common in aged dogs and reducing dietary fat helps in weight reduction. Manufacturers give little consideration to improving dietary quality. Some believe that elderly animals digest and absorb a meal as well as young animals. That conclusion is based on older animals having few changes in digestive tract morphology. But digestive function changes with aging.

Protein Needs of Older Pets

Quality of Diet
Older dogs require more protein than younger adult dogs. Merely increasing dietary protein does not satisfy this increased requirement. Protein quality must be improved. Dietary protein must become highly digestible. Overall dietary composition is important for optimum protein digestion and absorption. Dietary carbohydrates and fiber reduce protein digestibility by delaying its digestion. Normally, high quality dietary protein is completely digested and absorbed in the small intestine, and little or no protein enters the colon. Delay in protein digestion can cause some protein to escape digestion and absorption. Excess unabsorbed protein entering the colon is degraded by colonic bacteria to non-nutrient substances. These substances are absorbed and must be detoxified for excretion. Some of these substances are biogenic amines. Their colonic concentration increases with increased dietary protein.  Thus, in addition to commercial pet foods not supplying adequate protein for aged dogs, they also contribute to non-nutrient substances (some are toxic) because of poorer assimilation. High dietary fiber and poorly digested carbohydrates, such as in most cereal-based pet foods, aggravate this problem.

Protein Requirements
Dogs should be fed proteins with high biological value and high digestibility. This minimizes protein residue entering the colon where bacteria act on it to produce toxins. Protein requirements are satisfied by feeding 4.5 g of digestible crude protein per kilogram metabolic body mass (4.5 g/kg bw0.75) This level is 50 percent more than recommended for maintenance of adult dogs. However, commercial diets for adult maintenance often exceed this amount.

Caloric Needs of Older Pets

Food is consumed primarily to satisfy energy requirements. Older dogs and cats need fewer calories because they are less active than younger adults. To maintain optimal weight in old animals, caloric intake can decrease to 80 percent of that needed for younger adults. Total caloric intake reductions must take into consideration that requirements for other nutrients may be unchanged or increased. As already noted, dietary protein must increase even if caloric intake remains unchanged. Needs may increase for some vitamins and trace minerals, but that is unproven. Vitamin E is most important to supplement. Aging is associated with many degenerative changes and vitamin E helps prevent damage. Older animals are more likely to be overweight than younger adults. This greater tendency is specific for neither sex, and neutering is not significant in promoting obesity. The number of daily feedings is not a factor. Factors that do not make a difference include living with young children (who feed the pet frequently), raiding the garbage, or living with an older or younger person. The only significant factor associated with obesity in older animals is reduced physical activity.

Fat Digestion and Absorption
Fat digestibility and tolerance are not poorer in older dogs and cats but aging can delay fat absorption. Reduced fat intake is not necessary unless a weight reduction program is planned based on low-fat intake. Older animals require essential fatty acids so they should be given.

Carbohydrate Digestion and Absorption
Dietary carbohydrates are selected to increase digestibility for both starch and protein. Rice is the most completely digested carbohydrate. Dogs and cats poorly digest and absorb other grain cereals, the basis of most commercial pet foods. Although carbohydrate assimilation appears to be normal in older animals, in some dogs and cats it is associated with abnormal glucose regulation and signs of diabetes mellitus.

Nutrients Protecting Aging Animals

Chemicals and nutrients play a role in development of and protection against disease. Cancer is one such disease where some forms develop in humans consuming certain diets. Such a dietary effect is evident in humans eating a typical Japanese diet that is associated with a high incidence of stomach cancer and low incidence of colon cancer. In contrast, the typical high-fat American diet results in the opposite. The reason for these differences is unknown. Diet composition can affect mammary tumors. Diets low in methionine protect against tumor appearance and growth. Foods rich in methionine promote tumor appearance and growth. Chemicals in some diets are toxic and over time can cause diseases such as cancer. High dietary nitrosamine, for example, causes acute hepatic necrosis and chronic ingestion of lower amounts causes hepatic cancer. Some microorganisms produce dietary chemicals, such as aflatoxin produced by a fungus, that cause hepatic necrosis. Normal dietary constituents can be toxic and naturally occurring protectants minimize or prevent damage. Antioxidants protect against free radicals which appear as oxygen is used to produce energy. Antioxidants are important as dietary unsaturated fatty acids increase. These protectants include naturally occurring nutrients such as vitamin A, Vitamin C, and vitamin E. In addition, commercially‑prepared foods contain synthetic antioxidants such as butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), and ethoxyquin (ETO). Vitamin E is essential for cell membrane protection against the many chemical reactions generating free radicals. Vitamin E is more potent than synthetic antioxidants because it binds cell membranes. To be as effective, synthetic antioxidants must be given continuously and in large amounts compared with vitamin E. Membrane bound vitamin E loses its antioxidant activity on neutralizing free radicals, but other antioxidants such as vitamin C can restore membrane vitamin E antioxidant activity. Vitamin E appears to lengthen life span. When animals are given vitamin E from a young age, the onset slows for some age-related problems such as cataracts, cancer, cardiovascular disease, and decreased immune function. High blood vitamin E levels may lower the risk of some cancers. This effect can be due to vitamin E blocking the formation of carcinogens (such as nitrosamines from nitrates in the diet), inhibiting carcinogens from reaching cells, suppressing the effects of cancer and stimulating the immune system.   

Phytochemicals As Protectants
Phytochemicals are the source of nearly all phenolics found in animals. The important ones are phenolics. Phenolics essential for animals such as tyrosine come either directly from plants or are modified from essential plant precursors. Phenolic phytochemicals are grouped into flavonoids (such as anthocyanins, genistein and daidzein), tannins, lignans, and simple phenols such as the benzoic and cinnamic acids. These chemicals protect plants and have beneficial effects in animals. They protect animal cells by chelating, quenching free radicals, and providing an antioxidant. Phytochemicals are found in fruits, vegetables, grains and legumes; a human consumes about 25 to 35 milligrams daily. Soybean products are rich in flavonoids. Other beans are also rich in phytochemicals. In addition, natural blue, purple, red, orange and yellow foods are abundant in flavonoids. The benefits of flavonoids can be lost with food processing. Phytochemicals’ benefits can be enhanced by feeding substances that reduce intestinal absorption of toxins; such substances include soluble fiber. Flavonoids help control cancer growth. The flavonoid genistein prevents malignant angiogenesis, blood vessel development that promotes cancer growth. Genistein also promotes leukemia cell differentiation so they revert to normal cells. Some phytochemicals are toxic to intestinal bacteria. Reducing this bacterial population decreases toxin formation and absorption. Phytochemicals are beneficial only with dietary levels in naturally occurring foods. Excess phytochemicals can be toxic. Phenol-based compounds can be toxic; metabolism of any phenolic chemical releases phenol which is toxic. Owner-prepared diets should be formulated with a natural source of phytochemicals. Their beneficial effects for detoxification and protection should be lifelong.

Feeding to Reduce Cancer

The incidence of tumors is lower than expected in animals fed soy protein diets. Several soy protein constituents can inhibit tumor growth. They include isoflavones, phytosterols, protease inhibitors, inositol hexaphosphate, and saponins. Soy proteins are also deficient in methionine. Dietary soy protein instead of animal protein is associated with a lower incidence of breast and colon cancer in humans. No long term studies have been done in dogs and cats but the probability is great that feeding soy protein would have the same effects. A number of forms of soy protein are available. Many diets in this website are based on using one form, tofu, as the primary source of protein.

Feeding to Prevent Cancer Cachexia

Weight loss and cachexia are important complications of cancer. Cancer patients that maintain normal weight live longer and have fewer complications during treatment with chemotherapy, radiotherapy and surgery. Tumor cells uncouple metabolism which accelerates wasting and poor use of nutrients. Metabolic abnormalities affect use of carbohydrates, proteins, and fats resulting in many defects in nutrient usage.  Cancer patients are invariably anorectic and have a basal energy requirement that is twice normal, requiring food intake to be greatly increased. High-caloric density diet are fed to increase energy intake. Up to 50 percent of non-protein calories should be fat. High carbohydrate diets should not be fed. To improve anorexia, palatability should be enhanced by using animal fat such as chicken fat, seasonings such as garlic powder, and feeding food warm. No commercial pet foods meet dietary requirements for cancer patients.

Some studies suggest that a cancer patient's life can be extended by feeding a cancer-starving diet.  


1. Hawrylewicz EJ, Zapata JJ, Blair WH: Soy and Experimental Cancer: Animal Studies. J. Nutr. 125: 698S-708S, 1995.

General References

Hammer AS: Nutrition and Cancer: in Waltham book. p 75-85.

Garrison RH, Somer E: The Nutrition Desk Reference.  New Canaan, Connecticut, Keats Publishing, Inc. p.201-205.