Even though feeding raw first gained popularity with dog owners, cats truly are the ones that benefit the most from a species appropriate raw diet. Unlike dogs, cats are obligate carnivores, meaning they gain virtually all their nutrition from meat and animal products, and do not benefit at all from any kind of plant matter in their diet.
Even though both dogs and cats have no minimum requirement for carbs (they can easily get their required glucose from glycogen or amino acids), dogs can survive on many types of diets, even vegan ones, because their digestive system has evolved a lot in the past centuries. And even though an optimal diet is a raw meat-based diet, their bodies can easily take advantage of plant matter. They can derive some nutrition from plants as well as prebiotics but just because a dog can benefit and digest some plant matter, the plants chosen as a food source need to be carefully selected, especially when fed a raw diet. It’s important to avoid plants high in phytates which are readily found in cereal products, legumes (chickpeas, lentils, kidney beans, split peas, etc.), oilseeds (walnuts, hazelnuts, almonds, etc.) and seeds (sunflower, squash, pumpkin). Phytates are also present in soybeans and some tubers such as potato, yuca, taro and yams which are more recently listed in some commercially prepared canine diets. Phytates are highly toxic to dogs because of their function in the body – once consumed, they bind with many micronutrients making them unavailable for digestion, essentially making the good ingredients unused by your pet.
Cats, on the other hand, do not benefit from plants in their diet, even if frozen, cooked or soaked. In fact, plants can rapidly become anti-nutritional to cats, meaning they will have a negative effect on digestion and metabolism. So, for cats in particular, a switch from a highly processed, carbohydrate-heavy food, to a raw, species appropriate, meat-based diet without fruits and vegetables, will truly change their health and ultimately their life. The long list of benefits begins with improved oral health, smell and size of stools and urine, and improved urinary tract health. Cats that are fed a balanced raw diet without fruits and vegetables truly are in better overall health.
Cats have an extremely short digestive tract, which is very typical of a carnivore. When too many carbs are included in the diet, undesirable bacteria can start to develop. These bacteria may be beneficial for some species but can be harmful for cats. There are multiple categories of carbohydrates, from the absorbable simple sugars, fermentable starch and fiber, and undigestible fiber. Simple sugars will often have a bigger impact on the rise of blood sugar, while fermentable starch and fiber, and complex sugars, will promote the development of bacteria in the body at different stages of digestion, from the duodenum to the large intestine. A dietary imbalance, caused by feeding food with too many fermentable carbohydrates, often causes gas and bloating in both dogs and cats. As the bacteria ferment the carbohydrates, gas and strong odors make their “appearance” and more importantly this fermentation can impact protein digestibility and the digestibility of other nutrients, especially in cats.
Another example of how excess fiber and starch can impact digestion is taurine (an essential amino acid for cats). The taurine requirement for cats can increase up to 4 times the initial amount with the presence of fiber and starch in the diet. In short, taurine present in the food need to bind with the bile acids secreted by the liver to be available for absorption, but when there is too much fiber already binding with the bile acid, taurine is left on its own, promoting the development of bacteria that consumes the taurine before it is available for the cat. Cat food, even raw, that contain fruits and vegetables, should also be supplemented with extra taurine, while a raw meat-based diet, without the addition of fruits and vegetables will bring largely enough taurine to cover the requirements.
Unlike dogs, cats have a very low capacity for digesting simple and complex sugars. Digestive enzymes in the saliva and those secreted by the pancreas are very limited, or non-existent, making more of those carbs available for intestinal bacteria to ferment. There is also evidence to support the theory that cats are not able to adapt the level of digestive enzymes made in the pancreas to digest carbohydrates based on the level of carbs in the diet.
Processing and cooking carbohydrates slightly reduces their negative impact and begins the breakdown of the complex molecule making them slightly more digestible than they would be in their raw form which would be mostly fermented in the intestines and cause flatulence and bloating, as well as nutrient digestibility reduction.
For the very small amount of glucose that can be absorbed, there are also differences in cats that we do not see in dogs – mostly in the metabolization of glucose in the liver. These differences could explain why cats that are fed high carb diets are more prone to obesity, diabetes, and the inability to fast. Unlike dogs, cats do not have hepatic glucokinase activity, and no glucokinase gene expression – very typical for a carnivore. The role of the glucokinase enzyme, in other species like dogs, is to metabolize the glucose (glycolysis – breakdown of the molecule). This means that a cat is unable to react properly to a rapid rise in blood glucose, or a rapid need for blood glucose (fasting). Cats are simply not able to metabolize glucose adequately, they are designed to get their energy from fat and protein, or the small amounts of glycogen found in their prey. In fact, cats have a higher gluconeogenic (create glucose from protein) activity in their liver than dogs – meaning they are very well equipped for a high protein diet.
If weight loss or maintenance is the goal, a high protein, low carb diet happens to be much more effective in the reduction of fat storage than low protein, high carb diets, even if both contain the same total number of calories. Blood glucose being very strictly managed by the body, high carb intake results in high insulin secretion and a higher fat storage rate. The constant high secretion of insulin can also result in insulin resistance, which is unfortunately a very common disease in kibble fed cats (diabetes mellitus). A problem that is non-existent in wild cats and domesticated cats that are fed a species appropriate raw diet.
Some cat food, raw and canned, will still include fruits and vegetables, either as a filler (with added taurine and other amino acids) or as “prebiotics”. That is unfortunately a misunderstanding of what truly acts as prebiotics for cats. The inclusion of some prebiotics in a dog’s diet have yet to demonstrate the same positive impact for cats. Not all bacterial families are good, and therefore prebiotics (which, by definition, simply means food for gut bacteria) are not all equal and should be offered according to what type of bacteria we want in the feline’s gut. We know that carb-loving bacteria can create gas, excess fermentation, bloating, and overall, inflammation of the digestive tract so as a more species-appropriate alternative for cats, amino acids and fatty acids function as prebiotics. In fact, high quality amino acids and fatty acids can act as good prebiotics. Cats and dogs fed a raw meat-based diet have a significantly different and more diverse gut microbiome profile than those fed high carb diets. There are also some studies that evaluated the fermentation of certain amino acids, such as tryptophan, that seems to be linked to a reduction of inflammation and increase the gut barrier integrity. But that only applies to meat based, high quality amino acids, because feeding a poor-quality plant-based protein in excess can create putrefaction (bad amino acid fermentation) in the gut and cause chronic renal failure – which can happen when feeding processed plant-based proteins to cats.
Along these same lines, the potential of high-quality fatty acids (like polyunsaturated fatty acids – PUFA) as prebiotics is just starting to be studied and seems to have a major impact on good bacteria development in the gut and overall health benefits from the postbiotics (product of fermentation) of fatty acid “fermentation”.
Whether raw or kibble fed, we often view fiber consumption as necessary for our pets to avoid constipation when in fact, fiber has proven to be much less efficient than simply adding of probiotics (Thrive Pro-gut) to the diet. The change in the composition of the microbiome in cats seems to have a better impact on bowel movement than the extra fiber addition, not to mention avoiding all the negative side effects of extra carbs.
In conclusion, raw diets for cats should be formulated for their specific needs, and that means, low to no fruits and vegetables. Though not necessary for nutrition, plants can be fed in very small amounts, or for specific purpose (for example cranberries for the urinary tract, or seagrass for micronutrients), but are not beneficial as filler or “prebiotics”. In fact, additional carbohydrates often do more harm than good, so be careful of the raw food you choose for your cat, and make sure it is well adapted to their true carnivorous nature!
Reference:
Verbrugghe A, Hesta M. Cats and Carbohydrates: The Carnivore Fantasy? Vet Sci. 2017 Nov 15;4(4):55.
National Research Council of the National Academies. Nutrient Requirement for Dogs and Cats. Chapter 5: Fat and Fatty Acids. Animal Nutrition Series. 2006 (2018 edition).
Brady C. 2020. Feeding dogs: The Science Behind the Debate.
Wernimont Susan M., Radosevich Jennifer, Jackson Matthew I., Ephraim Eden, Badri Dayakar V., MacLeay Jennifer M., Jewell Dennis E., Suchodolski Jan S. 2020. The Effects of Nutrition on the Gastrointestinal Microbiome of Cats and Dogs: Impact on Health and Disease. Frontiers in Microbiology (11).
Sandri M, Dal Monego S, Conte G, Sgorlon S, Stefanon B. 2017. Raw meat-based diet influences faecal microbiome and end products of fermentation in healthy dogs. BMC Vet Res. 28;13(1):65.
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