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Problems From Feeding Commercial Pet Foods

Diets and eating habits can be related to medical problems and shorter life span. Six out of the 10 most common human diseases in the United States link directly to poor eating habits or dietary deficiency. Comparable data are not available for dogs and cats but it is likely that the nature of their diet has similar effects. This concern has been voiced to the pet food industry.

Pets are breaking down from disease at an unprecedented rate from a variety of problems. Why are so many pets getting cancers, renal failures, hepatic diseases, multitudes of skin and coat problems? Diseases and illnesses we simply shouldn’t be seeing. Illness and poor nutrition affect each other. With relatively large numbers of pets getting sicker and sicker, we should take a serious look at what we’ve been providing for them. Food is clearly not the only determinant of health, but it is one of the only health-related factors pet owners can control.

Surprisingly "most of our prehistoric ancestors had better diets and health than we do." Early humans foraged for food just like dogs and cats in earlier times. When foraging stopped, humans developed dramatic changes in one of few things that science can look at today, their skeletal structure. The changes were not due to evolution but to changes in diets and lifestyle. These changes put humanity on a path toward poorer, not better diets. For many, the poorer diets were based on eating corn. No longer foraging and eating more "perfect" diets, the foragers-become-farmers showed degenerative diseases not found in their foraging ancestors. The foragers were much more healthy and "almost totally free of internal parasitic infections." The conclusion is that "degenerative changes seen with aging develop after by a lifetime of neglect, in particular, eating improper foods and getting little exercise." Diets prepared for our pets today are very different from diets of a foraging animal. Current diets are based on cereals similar to humans' diets when they stopped foraging. A number of medical problems relate importantly to diet in dogs and cats.

Potassium Deficiency 

Deficiency of potassium causes clinical problems, especially in cats. Following the problem's understanding more potassium was added to commercial cat foods. It is not clear that current cat foods contain enough potassium. A drug company sells a product containing potassium gluconate which they recommend for administration to all cats. The company advertises that aging cats are "likely to share one common ailment: chronic potassium depletion." They go on to say "How widespread is hypokalemia? A recent university study discovered that 37 percent of regularly treated patients were hypokalemic." They recommend routine supplementation with their productapparently to correct a problem of inadequate potassium in commercial cat food. There is no evidence that potassium deficiency is or ever was a problem in cats that hunted or eat owner-prepared foods.

Gastrointestinal Disease

Persistent or Chronic Diarrhea
Fifty years ago few dogs and cats ate commercial pet foods as their primary source of nutrition. Problems of chronic diarrhea were uncommon compared to now. Today the average veterinary practice treats chronic digestive problems, mostly chronic diarrhea, more than any other internal medicine problem. The cause of frequent gastrointestinal problems may relate to widespread feeding of commercial pet foods. Many of these problems begin because pets eat such foods too early in life.
Allergy or hypersensitivity to foods is common and usually manifested by diarrhea and vomiting. Food allergies are common in dogs fed commercial pet foods. Food allergies are seldom recognized in countries where dogs do not eat commercial pet foods, where dogs eat owner-prepared foods. This difference is not the result of dogs living in an undeveloped versus a developed country. Italy is an example of such a country where food allergies are uncommon in dogs and cats that are not fed commercial pet foods. Commercial pet foods are made with ingredients having poor protein digestibility. Diets containing protein with digestibility less than 70 percent causes diarrhea in dogs. In addition, some fillers and extenders in commercial pet foods can cause chronic colitis in normal animals.

Acute Gastroenteritis
Acute diarrhea and vomiting have many causes. Bacteria and their toxins are an important cause. Commercial pet foods (dry) are contaminated with bacteria. The numbers present may or may not cause problems. Improper food handling and certain feeding practices will greatly increase the likelihood of problems. For example, moistening a dry food and allowing it to remain at room temperature results in multiplication of its bacteria. The increased numbers can cause acute gastrointestinal problems. Some pet food products print recommendations (on their label) to moisten dry food and make it available at all times beginning when a puppy is 3 to 4 weeks of age. This recommendation can cause acute gastrointestinal problems.
Contamination of commercial pet food with bacteria or microbial toxins can cause acute gastrointestinal problems and sometimes results in a company recalling the product.

Persistent or Chronic Vomiting
Vomiting often accompanies the diarrhea and usually has the same causes.

Reflux Esophagitis 
Vomiting caused by reflux esophagitis occurs in some animals fed commercial pet foods in a single daily meal. The problem can usually be managed by a different feeding practice.

Bloat or Chronic Gastric Dilation
Bloat is a serious often life-threatening problem more commonly seen in larger size breeds of dogs. The cause of the problem is unknown but affected dogs lose their ability to belch swallowed gas and to vomit. It results in gastric retention of gas, fluid and food. Without decompression to remove the accumulated gas, shock develops and death is common. The frequency of bloat increased as the number of dogs consuming dry commercial dog food increased. Bloat frequency is much lower in countries where dogs are fed home-prepared diets rather than commercially-prepared pet foods. Most veterinarians recommend changes in dietary management for dogs recovering from bloat because such individuals are very likely to bloat again.

Liver Disease

Liver Disease in Cats
Hepatic lipidosis does not occur in cats living in the natural state. Affected cats have usually been fed commercial pet food. Cats overeating on such diets are more likely to develop the problem. The problem is usually very serious and life-threatening.

Liver Disease in Dogs
Dogs have many very different forms of liver disease. With all, the progression of hepatic disease requires ongoing hepatocyte damage. What a dog is fed directly affects continuing damage. With most forms of hepatic disease, the continued feeding of commercial dog food is followed by death in a predictable time. On the other hand, animals live if they do not eat a commercial food but are fed a diet based on protein from milk or soybeans. Ongoing hepatocyte destruction can stop when these proteins replace meat in the diet. In most cases the initial insult is gone and an optimum diet supports recovery. If an insult continues to damage hepatocytes, liver damage is likely to continue and be more severe in dogs fed commercial pet foods than owner-prepared and meat-free diets. Hepatic disease can cause signs of hepatic encephalopathy that include convulsions, weakness, blindness, staggering, walking in circles, and stumbling. This problem's cause is unknown but it can be managed by feeding a meat-free diet. The diet should also be low in methionine and ingredients promoting ammonia formation.

Urinary Tract Disease

Urolithiasis in Cats 
Caclculi in the feline urinary tract plugging and blocking urination is directly related to diet. Urolithiasis is rare in cats fed meat-rich owner-prepared foods and cats hunting for food. The problem appeared with the feeding of commercial cat foods. Its cause was eventually understood and pet food manufacturers changed cat foods to reduce the frequency of urolithiasis.

Urolithiasis in Dogs
Many urinary tract calculi form in dogs because of infection. Many also develop because of the diet. Some calculi were rare before feeding commercial dog foods became so common.

Renal Disease in Dogs and Cats
Renal disease is common in dogs and to some extent in cats compared to other animals. Progressive renal damage, once a problem develops, relates to dietary calcium and phosphate concentrations. The progression of damage is also affected by dietary vitamin D because it promotes intestinal absorption of calcium and phosphate. Excess absorption of these minerals cause calcium crystal deposition and renal damage. Feeding commercial pet foods that are usually high in calcium, phosphate and vitamin D worsens renal damage. All meat diets also contain high phosphate levels but low calcium levels. This combination stimulates release of calcium from bones which can also lead to calcium deposition in renal cells.

Heart Disease

Feline cardiomyopathy, develops in cats and some dogs fed diets containing insufficient taurine. This problem never appears in cats hunting or eating owner-prepared diets. It occurs when cats eat commercial cat foods containing insufficient or no added taurine. Manufacturers now fortify commercial cat foods with taurine.


Blindness develops in cats fed diets deficient in taurine. This problem was recognized before the taurine-deficiency-induced cardiomyopathy. When the problem was understood and taurine was added to cat foods, some diets were still deficient so that the other taurine‑deficiency problem could appear. Cataracts are a common problem in older dogs. The cause of some relates to feeding a diet high in sugar. This kind of diet is unnatural to dogs, even if they are now omnivorous.

Orthopedic Problems

Larger-sized dogs have a high incidence of orthopedic problems such as hip and elbow dysplasia. They are important and often serious medical diseases that can require surgical correction. An important reason these diseases develop is rapid growth that leads to bone deformities. Feeding excess calories promotes rapid growth. Excess calories are fed with high-caloric-density commercial dog foods. Commercial foods for growing dogs are formulated to promote rapid growth.

Skin problems

Skin and hair coat quality are determined mostly by diet. Pet foods contain proper amounts and kinds of fats to insure their high quality. Pets can develop skin allergies because of feeding practices, however. The problems develop because very young animals begin to eat commercial pet foods before their immune system is mature enough to protect against allergies developing. Manufacturers make no attempt to formulate diets appropriate for weaning puppies and kittens. Some dogs can also develop unwanted body odors from eating commercial pet foods

Endocrine Diseases

Diabetes Mellitus
Diet can be very important in the management of diabetes mellitus. This problem can appear because of obesity and can improve with a high fiber diet.

There is evidence that hyperthyroidism in cats results from feeding commercial pet foods. Caused by a tumor or nodule of hyperactive tissue in the thyroid gland it is a new disease (appearing after 1970). Hyperthyroidism appeared with the feeding of canned cat foods. The disease does not occur in developed countries where owners do not feed canned cat food. With the feeding of canned cat foods the problem is appearing there. It is unknown how canned cat foods cause this thyroid abnormality. If hyperthyroidism was an unimportant disease the feeding of cat canned pet foods could continue. The disease is serious, however. Besides losing weight and having a continuous problem with diarrhea, affected cats' personalities change so that many animals do not remain enjoyable pets. Treatment of the problem is costly and can be life-threatening. Cost of treatment is usually high and is not always successful; some cases are fatal.

Behavioral Problems

Coprophagy is rare in animals fed owner-prepared diets or consuming food caught while hunting. Coprophagy is common in dogs fed commercial pet foods, especially dry foods.  Coprophagy is associated with feeding high carbohydrate diets, especially in German Shepherds. Coprophagy ceases in working dogs fed horse meat instead of dry dog food where caloric intake remains unchanged. Enough horsemeat is fed to reduce the diet's carbohydrate content from about 40 percent to about 25 percent. Instead of correcting the nutritional problem causing coprophagy, pets are often fed something to give feces an offensive odor and taste. Chemicals for parasite control are sometimes given orally to discourage coprophagy. Sodium glutamate mixed with a purified edible vegetable protein fraction is marketed with claims for curbing coprophagy. It also makes the odor and taste of feces offensive. If a pet eats fecal material of other animals, these preparations have no value.

Summary and Conclusions

Nutritional problems are uncommon in dogs and cats when they hunt for food and adequate amounts are available. Nutritional abnormalities developed when animals were domesticated and they no longer had a choice in what they were fed. Many other nutritional problems appeared with the feeding of commercial pet foods. Some problems appeared because pets are fed foods not designed for carnivores. Deficiencies resulted due to pets consuming incomplete diets. Other problems appeared because of knowledge being incomplete for dog and cat nutrition. Some problems appeared because of food additives in commercial pet foods. An important cause of problems is contamination of pet foods with microorganisms, primarily bacteria, and toxins.


1. Grunberg R. Nutrition and disease. Petfood Industry. July/Aug 1995??  P. 50.

2. Bryant, Vaughn M. Eating Right Is an Ancient Rite. The World and I.  vol 10 no. 1  pp 216-221.

3. The potassium supplement is sold by Daniels Pharmaceuticals, Inc., St. Petersburg, Florida under the brand name of Tumil-K.