I have been told that it’s not a good idea to feed dry food at the same time as raw food, and that it’s even bad to feed some kinds of canned foods in the same meal as raw foods. Why is this? Will a meal that has been processed, cooked foods, and raw meats make my cat ill? What is it in some processed foods that causes problems when eaten with raw foods?
As a raw feeding vet I am often asked how a raw diet can make such a difference to our cats’ health. The simple answer is that by feeding a species-appropriate diet, the digestive tract of the cat is fully functional, and all the natural nutritional goodness of a raw diet can be fully absorbed and utilized by the cat’s body. Cats are adapted to preferentially use protein and fat as an energy source. In their natural habitat, they consume prey that is high in protein, with moderate amounts of fat and minimal amounts of carbohydrate. Although cats can use carbohydrates as a source of metabolic energy, they have a limited capacity for carbohydrate digestion.
So, what happens when we raise the level of carbohydrate we expect our cats to digest?
If a cat is fed high-carbohydrate food at the same time as raw food, the carbohydrates can interfere with the efficient absorption of the nutrients in the raw food, potentially cancelling out the benefits of the raw diet. Increased levels of crude fibre in feline rations increase faecal output, alter colonic microflora and fermentation patterns, alter glucose absorption and insulin secretions, and at high levels can depress diet digestibility.1
What do we mean by depressing diet digestibility?
To understand how a food is digested, we need to take a journey through the intestinal tract of a cat. Imagine the digestive tract as a production line. If the first person in the line is inefficient, then the rest of the line can’t hope to do their job properly. In the cat, the mouth is for ripping and tearing. There is no salivary amylase to digest carbohydrates, so the first stage in the digestive production line is the stomach. The cat, being an obligate carnivore, has a very acidic stomach, with a pH of 2, ideal for digesting protein and neutralising bacteria.
Many processed pet foods have significantly increased the carbohydrate content of their cat foods, and have substituted animal proteins with plant-based proteins. The problem with this substitution is that it does have an impact on the digestive environment. In a cat eating a high carbohydrate-high plant protein-lower meat protein diet, we find that the acidity in the stomach changes. Gastric acidity is dictated by the meat content of the diet. The stomach becomes progressively more alkaline, heading for a pH of 4 or above. In this less acidic environment, several problems arise in the first part of the production line. Gastric emptying slows down, contaminating bacteria are not destroyed, and raw meat and bones are not softened or broken down effectively as the digestive enzymes in the stomach only work in a very acidic environment. Feeding processed foods at the same time as raw foods can lead to the entire meal not being completely digested in the digestive tract.
Stomach acidity is the major regulator of pancreatic and liver ability to respond to food arriving in the small intestine. Food arriving in the small intestine with a pH of 2 or less triggers the release of two very important hormones, secretin and cholecystokinin. These two hormones are so important that without them, normal digestion of food just can’t happen. The pancreas does not produce its juices and bile is not secreted to digest fats.
The result is maldigestion and as a consequence, malabsorption.2 Maldigested carbohydrates get consumed by abnormal gut flora which flourish in the altered pH of the digestive tract. Fats are not digested, resulting in deficiency in the essential fat soluble vitamins, A, D, E and K.3 When incomplete digestion of starch and disaccharides occurs, it leads to an acidifying effect on the pH of the faeces, due to the fermentation of the undigested starches and disaccharides in the intestines. A change in pH at any point along the digestive tract will affect the efficiency of the digestive tract. Digestive enzymes function within a specific pH range, and gut flora is also affected by changes in pH. The link between an abnormal gut flora and compromised immunity has been established in man and animals.4
To digest cooked foods, the cat’s digestive system must work a bit harder than to digest raw foods. Raw foods come with live enzymes to help in the digestive process, while cooked foods are less alive. Often, a cat who has never had raw food can be tempted to eat a raw diet by using cooked foods that he is familiar with. Mixing the familiar cooked or tinned high-meat content food with a little raw food can be a good starting point when transitioning. My best advice is not to try to transition a cat with a mixture of dry processed food and raw food. The carbohydrate content of dry food will reduce his ability to fully digest his raw food, and will make him vulnerable to bacterial infection. When you make a commitment to raw feed, get the biscuits out of the house!
With the increasing realisation that many diseases in cats are a result of disease in more than one organ system, the importance of the digestive tract in all diseases is not to be underestimated.5 As Hippocrates said: “All disease begins in the gut.”
1. Ellen Kienzle, “Effect of Carbohydrates on Digestion in the Cat,” The Journal of Nutrition, no. 124, 1994, 2568S-2571S.
2. ME Matz and WG Guilford, “Laboratory Procedures for the Diagnosis of Gastrointestinal Tract Diseases of Dogs and Cats,” New Zealand Veterinary Journal 51, no. 6, December 2003, 292-301.
3. ME Matz and WG Guilford, “Nutritional Management of Gastrointestinal Tract Diseases of Dogs and Cats,” New Zealand Veterinary Journal 51, no. 6, December 2003, 284-291.
4. R Fuller, “Probiotics in Man and Animals,” The Journal of Applied Bacteriology 66, no. 5, May 1989, 365-378.
5. CAT Buffington, “Idiopathic Cystitis in Domestic Cats - Beyond the Lower Urinary Tract,” Journal of Veterinary Internal Medicine 25, no. 4, Juliy/August 2011, 784-796.