Why Did My Dog Or Cat Develop Digestive Tract Issues While Other Pets Didn’t


Why Did My Dog Or Cat Develop Digestive Tract Issues While Other Pets Didn’t?

IBD, Intestinal Lymphoma Chronic Diarrhea, Pancreatitis,Gall Bladder and Liver Issues etc.

Ron Hines DVM PhD

 Similar problems in Dogs 

 Similar problems in Cats 

 What Should I Feed My Dog?

Many health issues that occur in life happen because they have a strong genetic inclination to occur. That’s something we can’t control – yet. But the genetic destiny of your dog and cat can be modified by its lifestyle and life events. You have a lot of control over that when it comes to a group of chronic inflammatory disease that affect dogs and cats. 

The increased diagnosis of these chronic digestive tract issues in pets parallels the switch from their more natural foods to mass produced canned and dry pet diets. They are much less common in dogs and cats in other parts of the world that have not follow that trend. In those places it is intestinal parasites, virus and infectious bacteria that are the leading causes of intestinal inflammation. Here in the western developed world, periodic broad-spectrum worming medications, vaccines and sanitation have reduced the risk of infections. Chronic intestinal, liver, gall bladder and pancreatic inflammatory issues are now the major diseases confronting dogs and cats. Read about that in cats here.  It is no coincidence that all the organs involved are involved in process incoming nutrients. 

Dogs, because of their longer association with people and time to adapt genetically to high carbohydrate human diets, might suffer some of these digestive tract issues less frequently than cats do. Over time, dogs developed genetic mutations that allowed them to process carbohydrates better. ( read here & here)  However, that increased ability of dogs to digest carbohydrates is not uniform among breeds or individual dogs. (read here here)  Cats became our partners considerably later. (read here)

There are almost always early hints of a future digestive tract issue while your dog and cat are still quite young. You or your veterinarian might write it off as a case of indigestion, an inappropriate food item, fur balls, etc. But generally, these problems get worse as the years go by.

The general thought within the veterinary research community is that chronic inflammatory digestive tract problems in cats and dogs have similar causes to those in humans. (read here) And because very few unbiased nutritional studies have been performed in pets, veterinarians rely on advances in our understanding of the chronic diarrheas and intestinal issues of humans regarding what might causes them and how they might be successfully treated. Basic metabolic and immune processes do not differ that much between you and your cat or dog. Realizing that has been used successfully by veterinarians many times in the past. 


The Genetic Component Of Your Pet’s Digestive Problem

Veterinarians know that certain breeds of dogs are more susceptible to inflammatory bowel disease than others. (read here) In humans, we know that many inflammatory bowel sufferers have mutations in their Interleukin-10 genes. (read here) Interleukin-10 puts limits on inflammation. In nature, gene mutations are not always bad. Often we later discover that those mutations persisted from generation to generation because having them confers advantages as well as disadvantages. But dogs, cats and humans have been removed from genetic selection for positive health traits for a long time. For example, inflammatory colorectal polyps in dachshunds are thought to constitute a breed-specific form of inflammatory bowel disease. Dachshunds appear to be genetically predisposed to this form of illness. About a third of them have evidence of generalized gastrointestinal inflammation as well. Another evidence of strong genetic involvement is that if one kitten or puppy in a litter develops chronic intestinal issues, it is much more likely that others in that familial line will as well. 

Genetics Diet And Intestinal Bacteria Working Together

Your dog and cat’s digestive tract health relies on all three of these components working together in harmony:


The bacterial community (aka microflora, biome, gut flora, microbiota ) that are normal residents of your pet’s digestive tract play a very important part in intestinal stability. One study at Texas A&M University determined that two species of bacteria decreased in number during periods of diarrhea in dogs. (read here) Another found significant differences in the bacteria residing in normal dogs versus those with diarrhea. ( read here here)  Similar changes occur in cats with digestive tract issues. (read here)  As in humans, bacterial diversity in pets with intestinal issues tends to go down. (read here)

We know that the microscopic organisms present in your pet’s intestine constantly interact with the immune system cells in the pet’s intestinal walls that surround them. More of these organisms are present in its large intestine than its upper small intestine and stomach because conditions farther down the tract are more friendly to their survival. It is critical that a “normal mix” of these organisms exist to suppress the bad ones among them. The “normal mix” is dependent on the nutrients passing through the digestive tract. That is dependent on what nutrients are being consumed. (read here) The  body’s immune system constantly monitors what passes through the intestine. In circumstances where the bacterial mix is wrong or where food components such as carbohydrates, food additives and contaminants modify intestinal conditions, “healthy” microflora can lost and replaced by organisms that are not the norm for the species. In those situations, the animal’s immune system can make errors and identify a basically non-threatening food, bacterial ingredient or even its own body tissue (autoimmune disease) as a threat. (read here ) Once identified as such, a process of intestinal inflammation begins that can be very difficult to stop – even when the microscopic organisms, the original source of the error, are no longer present.  Immune errors like these don’t only occur in the intestine. They are the basis of all autoimmune diseases. Many of the diverse healthy intestinal microorganisms in your pet were passed to it from its mother through its milk and skin contaminants. (read here & here)  Once lost to antibiotics or inappropriate diets, these “good” bacteria can be very hard or even impossible to reestablish. Compounding the problem are the effects of that period of unhealthy intestinal environment on your pet’s immune system. Once a pet’s immune memory cells are programmed as to how they respond to the intestinal environment, they retain that memory long after irritating dietary ingredients or undesirable bacteria are no longer present. 

Are Probiotic Pastes or Probiotic-Containing Pet Foods Likely To Help? What About Prescription Intestinal Diets?

Of the 42 different bacteria types identified in the stools of health dogs, none that I know of are included in the probiotic pastes and additives sold for dogs and cats.  (read here) There appears to be very little difference between the normal intestinal flora of cats and the normal intestinal flora of dogs so I doubt that these products are of any long term help for cats either. (read here) Prescription diets like Hill’s i/d line, Purina’s EN or Royal Canin Gastrointestinal are often bland enough to calm your pet’s intestines. But they do not address the underlying problem of dysbiosis. The better option is a fecal transplant. (read here) But co-habitation and food sharing with a health pet allows bacterial transfer too. After all, that’s how they got their intestinal flora in the first place. 

The Problem Of Chronic Digestive Tract Inflammation-What Is Going On In My Dog Or Cat’s Digestive Tract

Your pet’s digestive tract must be a permeable enough sieve to let nutrients in. But invaders want in too. So its body has guard cells present to regulate what gets in and what doesn’t. That is one of the duties of the immune system. Gatekeeper cells are present within the intestinal walls. (read here) In pets with one of the chronic intestinal inflammation issues like IBD, the immune system gatekeeper cells mistakes food, bacteria, or other materials in the intestinal tract for foreign substances that should not be allowed in and responds by sending messages (inflammatory cytokines) that result in white blood cells (primarily neutrophils) entering the intestinal lining.  These neutrophils liberate their own mediators in an attempt to neutralize the perceived (but mistaken) threat. The result is chronic inflammation. What you will see is diarrhea or abnormal stools, increased stool frequency and/or vomiting, decreased appetite and perhaps weight loss. The process is highly complex. (read here) Thickened, inflamed intestines do not absorb nutrients well. So a host of secondary sighs of malnutrition such as anemia are also possible. (read here) Accessory organs of the digestive system, the liver, pancreas and gall bladder are commonly affected as well. (read here)

In cats with inflammatory bowel disease it is often lymphocytes that accumulate in the intestinal walls. That form of inflammation can eventually morph in lymphoma. In other cats, eosinophils accumulate in the intestinal walls. That is characteristic of one form of intestinal, skin and/or digestive tract disease called eosinophilic granuloma. See previous link & here. In dogs a similar lymphocyte driven inflammation is rarer but possible as well. 

Is Every Case Of Intestinal Inflammation In Dogs And Cats Linked To Their Diet?


“Every” is never an appropriate word to use in medicine – the body and the influences of the world around it are just too complex. 


Are Commercial Pet Diets Really As Meaty And Natural As The Companies Selling Them Would Have You Believe?  


It is all smoke and mirrors. I would disregard whatever large and small manufacturers say about the benefits of whichever diet they are marketing at the time as well as the results of supposedly neutral scientific studies underwritten by the dog and cat food manufacturers. Tufts runs a lot of those company-paid-for “studies”. But Davis and Royal Dick are not above doing so now and then either. 

Are Carbohydrates  Really All That Bad? The Pet Food Companies Tell Us They Are Great For Dogs and Cats ! They Tell Me They Are Grain Free

They may be grain free, but they are not plant carbohydrate free. The companies just substitute non-grain carbohydrate sources such as peas and potatoes. The amount of carbohydrate in the food you feed your dog or cat has a crucial influence on the types of bacteria that can survive in its intestines. (read here) Humans tolerate – even thrive on carbohydrates. Our pets have different needs. Whatever ability they have to tolerate high carbohydrate diets is most developed in dogs. It is very poorly developed in cats (read here) and totally lacking in ferrets. There are two important forms of carbohydrates, first the sugars and starches and second the fermentable fibers like the beet pulp you see on the label. The presence of either or both influence which bacteria will thrive in the intestine. (read here)  Most dogs tolerate moderate amounts of starch in their diets, but sugars and starches have major negative consequences for cats. The second form of carbohydrate, fiber (cellulose), can have beneficial effects in producing regular bowel movements in dogs and cats, as it does in humans or in a weight loss plan designed for your pet. Low carbohydrate diets have already proven their worth when cats develop diabetes and many believe the high carbohydrates in commercial cat foods, along with the obesity they generate, are a major cause of feline diabetes as well. Veterinarians have also noticed a link between inflammatory bowel disease and pancreatitis in cats. (read here & here) Even the most common liver disease in cats, (hepatic lipidosis) , has been linked to these obesity-generating, carbohydrate-packed commercial cat diets. (read here) Humans with Crohn’s type chronic bowel inflammation are four times as likely to develop pancreatitis. (read here)

Well, If The Companies And Veterinary Nutritionists Know Carbohydrates Are Not Required, Why Do The Include So Much Of It In Their Products?

There are two reasons: The cost of ingredients and the dry kibble manufacturing process itself. In the case of canned products, only the first applies.

The pet food and pharmaceuticals market are among the most profitable consumer product industries in the world. (see here  Keeping ingredient costs down and purchase price high is a time-honored way to do that.

Dry pet foods are generally made by mixing the ingredients and pressing them through a small opening (die extrusion) at high temperatures.  In this process, carbohydrates act as the glue to bind the other ingredients together. I am not an extrusion technologist; but I believe that if the large pet food companies could produce a profitable dry kibble product for dogs and cats with more than 36% protein they would have already done so. They are not ones to neglect a potential market. The only company I know of with the philosophy and that claims to have perfected manufacturing techniques to get around that is Wysong™.

Are There Additives and Compounds In My Pet’s  Foods That Could Potentially Increase Its Chances Of Developing Digestive Tract Issues?

Probably so.

You yourself probably eat many of those ingredients as well. However, you do not eat them day in and day out in large quantities like your pet does. Development of the  knockout mice I told you about earlier has made it much easier to tell which things in one’s diet have the potential to trigger a malfunction of the intestinal immune system. (read here & here) Certain knockout mice have been bred to be deficient in interleukin-10, a cytokine that puts limits on intestinal inflammation.  Because of that it is called an anti-inflammatory cytokine. All these mice eventually develop inflammatory bowel disease, but what they eat and other factors in their environment make IBD appear earlier in their lives. 

Emulsifiers, Jellers and Thickeners

You already know that a typical can of cat or dog food is about two-thirds (78%) water. That appears to be about the maximum amount the producers can conceal in their products without it being apparent to you. Pet food manufacturers know that pet-owner perception is everything and that you wouldn’t be happy if you opened the can and saw that the top two-thirds was water. So they add emulsifiers to distribute the water evenly, and jellying agents to thicken it up.

There is a growing body of evidence that these emulsifying/thickening products have the potential drastically alter the type and number of bacteria found in your pet’s intestine. (read here)  Emulsifiers are also thought have the potential to encourage inflammatory bowel disease by stripping the pet’s intestinal wall of its protective mucus layer. Without that separating barrier, bacteria and undigested pet food ingredients are much closer in position to your pet’s immune system cells. Perhaps that forces the immune system cells to make snap decisions regarding the potential danger of food and bacterial antigens. Decisions that could be in error.  (read here) Some of these additives are also irritating in their own right.

Pet food manufacturers and their fellow travelers will reply that all these additives have been approved by the FDA or the EFSA. That is true. However those studies were done long ago – long before intestinal inflammation problems began to rise in humans, dogs and cats and before scientists had any knowledge of the importance of the  intestinal biota . When clearance was given to those additives, knowledge of how immune system’s memory and defenses functioned was also rudimentary.

The most common emulsifiers/thickeners in canned pet foods are carrageenan, cassia gum, guar gum, cellulose gum/ (aka  carboxymethylcellulose), and  xanthan gum that you might see on the ingredient labels. The kelp and saccharina  are added to perform a similar thickening function – not because of any known healthful effects in dogs or cats.


In one study, carrageenan, at least in the presence of other cancer-causing agents, was thought to accelerate the disease in animals. (read here) Its pro-inflammatory effects in humans trouble me too. (read here)

Cassia gum

This emulsifying and jelling agent has no nutritional value. The European Food Safety Authority found that cassia gum had the potential to cause irritating and sensitizing effects. (read here & here)

Guar gum

Guar gum is an economical additive for pet food manufacturers because it has almost eight times the water-thickening potency of cornstarch. It is cheap and only a small quantity is needed for producing a stiff texture in almost anything – even pure water.  It is used a lot in the food industry but the biggest use today in the US is in the petroleum fracking process where it is injected into the ground and in sewage plant water purification. It appears to have the potential to be irritating in its own right and to sensitize the immune system. (read here,  here  & here


Maltodextrin is another thickening and binding agent loved by the pet food industry. It is often added to commercial pet treats (particularly the soft or chewy ones). It is also the most major ingredient in the Fresh Breath Cat Treats sold at PetSmart). It too was found to found to disrupt the colon’s mucus barrier and allow bacteria to cling tightly to the intestinal walls. (read here  &  here)  Products like these that alter optimal conditions in your pet’s intestines have the potential to effect processes far from the digestive tract – recent studies in children reveal that. (read here & here)  


Dogs and cats choose their food based on smell, taste and mouth feel – not color. Cats make their decisions based on the same factors. Those bright artificial colors are added to pet foods solely to induce you to buy them. That also goes for those eye catching images of the contents that are printed on the sack. I often wonder if the sac might be the most expensive part of the purchase. Rest assured nothing like those mouth-watering food chunk images are inside. Many associate those dyes with a variety of health issues. (read here)

Meat Proteins Taken To Very High Temperatures

When the meats used in pet foods are initially processed, they are first dried by exposure to significant heat. When the cans containing the final product are sterilized, they are exposed to further heat. When dry pet foods are extruded into pellets, they are exposed to temperatures of up to 170 C (some sources say temperatures reach 204 C) to bond the ingredients together. Heating meat to high temperatures causes the generation of two groups of chemicals known to stimulate cancer, HCAs (heterocyclic amines) and PAHs (polycyclic aromatic hydrocarbons). HCAs are thought to begin to form in meat at about 150 C. The longer the meat remain at high temperature, the more it is formed. We know these compounds are suspects in the cause of colon cancer in humans. In one study, chronic intestinal inflammation preceding the cancer made people 6 times more likely to develop it. (read here) How and if this relates to intestinal disease in cats and dogs I cannot say because no one has examined the issue. Diets marketed for allergic pets such as Hill’s i/d line, Purina’s EN or Royal Canin Gastrointestinal are all hydrolyzed to break down the protein that they contain. Hydrolysis requires the application of high heat. (read here)

What About The Fat Levels In My Pet’s Diet?

Dogs and cats handle animal fat in their diets better than we do. They seem to be immune to the fat-associated cardiovascular problems we humans are prone to. Cats in particular require substantial more fat in their diets – more than is found in lean meat. Dogs don’t need as high a level, but handle 10-15% dietary fat content well. Too much fat in your cat’s diet is not desirable either. (read here)  However, when intestinal inflammation, pancreatic, liver or gall bladder disease become a problem, your pet may no longer tolerate fat or absorb vitamins as well as it once did. Those cats might benefit from a fat-soluble vitamin supplement. (read here)  Some commercial pet foods contain fat that is “hardened” with hydrogen gas to make the product more appealing to you. The label might say, contains hydrogenated fat or just fat. One study found that that type of fat (trans fat) had the ability to cause liver damage in cats. (read here) Because of health concerns, the FDA banned the use of trans fats in all human food in 2015. However, at the request of animal food industry lobby, pet foods were exempted from the ruling.

How About Fiber?

It is normal for cats to nibble on fiber now and then. In the wild, 20-26% of their feces contain small to moderate amounts of grass and other native plant material. (ask me for Moleon2003 & Sarmento1996). Perhaps dietary fiber aids in bowel movement regularity. No data exists for wolves, so we really do not know. A variety of commercial pet foods add highly processed sugar beet fiber, a waste from the sugar industry to their pet food lines.  Although beet pulp is sold as a horse feed, I suggest you use a human grade fiber products instead if you are trying to increase your pet’s fiber consumption. Extra fiber can contribute to healthy weight loss; but too much leads to flatulence, soft stools, diarrhea, and malnutrition. There have been human studies that link low fiber diets to the development of IBD. However, once the disease is present, high fiber diets tends to exacerbate (make worse) IBD symptoms. We do not know the influence of dietary fiber on dogs and cats with intestinal disease. The only way you would know would be to ad a small amount of human-grade fiber product to your pet’s diet and observe how its stool consistency and frequency is influenced.

If I Put My Pet On A Low-carb Additive-free Diet Will It Get Better Or Maybe Even Cured?

By all means try. Many pets improve or go into remission when their diets are changed. You already know that my preference is for diets you prepare at home. Those are the only diets whose ingredients are fully under your control. But once your cat or dog’s immune system decides that a dietary ingredient, a bacteria its intestines or something else consumed is a threat to its body, that decision  becomes part of your pets immunological memory , that can be very hard or impossible to erase. Drugs like corticosteroids or cyclosporin can suppress that memory; but the same immunological memory is there to protect your pet against infectious disease. 

What If My Vet Tells Me The Problem Has Already Morphed Into Lymphoma?

It can be quite difficult for veterinary pathologists receiving intestinal biopsy samples from your cat or dog to tell the difference between inflammatory bowel disease and the early stages of lymphoma cancer in cats or in dogs with certainty. (read here & here) Cat owners write to me frequently. In the cases where their pet’s chronic inflammatory intestinal problems had progressed to cancer the cats have never lived very long. I tend to discourage pet owners like you from having cytotoxic drugs, quack or unproven remedies given to your pets in those situations. There are veterinary schools and veterinary oncologist who will do it. But time gained, if any, tends to be brief. You love your pet more than they do; decide if it is really a kind thing to do. 

Should I Prepared My Pet’s Diet At Home?

Like home schooling your children, it gives control back to you. But like home schooling, you have to be quite committed and educate yourself. You will have to sort through the tremendous amount of information, disinformation, hype and scientifically unproven claims that litter the Internet and print. You cannot rely on the advice of those who offer to sell you their amazing products and supplements with great hype and fanfare. The fact that a pet diet is sold fresh in a grocery store only guarantees that its likelihood of containing salmonella is greater. The pet food industry and their many fellow travelers as well as the AVMA will do their best to scare you out of it. They will insinuating that even the most enlightened pet owner does not have enough common sense to prepare a nutritionally complete diet for their dog and cat. Do you call your nutritionist every time you prepare a meal for yourself or your children? Lest you rush out and purchase the ingredients and plan to feed them to your pet raw, remember that feeding raw meat ingredients can present its own dangers – particularly to pets that are already in ill health with reduced intestinal defenses. Although some folks successfully feed raw diets, I lightly cook all meat ingredients and select those individual ingredients myself. (read here)


I have an affection for ferrets as well as dogs and cats. (read here)  Ferrets have had zero time on their historic scale to adapt to a human high-starch diet. So it is not surprising that ferrets are even more susceptible to Carbohydrate Glut than dogs and cats. Wild ferrets are called polecats.  In the summer, rodents, small rabbits, frogs and an occasional bird are their major food. Ferrets are designed slender enough to stalk those small creatures within their burrows. In the ferret’s native habitat, there are plenty of  available carbs; but those abundant fruit, berries and tubers are never touched. Consequently, they have an extremely short intestinal tract designed to process meat. It is no wonder then that substantial amounts of carbohydrate (which they will readily eat) make them ill. It is not uncommon for their pancreas to be so over-stressed dealing with these carbohydrates that cancers form there. (read here) Or they develop sudden or prolonged intestinal crises like inflammatory bowel disease. (read here)

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