The Carnivore Connection to Nutrition in Cats
In another time long ago, Leonardo da Vinci said "The smallest feline is a masterpiece." And for those of us who marvel at the wonder that is a cat, there is no doubt that this statement was remarkable for its simplicity as well as its truth. Cats are amazing creatures, unique and interesting in almost every way imaginable. Despite this, it has been common for veterinarians to consider cats and dogs as similar beings for anesthesia protocols, clinical diseases, and treatments. However, it is quite clear that cats are unique in all conceivable ways, particularly in their nutritional biochemistry. Cats are strict, obligate carnivores that rely on nutrients in animal tissues to meet their specific and unique nutritional requirements. This statement is news to few, yet the importance of these nutritional differences is often underestimated, especially during periods when cats are ill, or have prolonged anorexia. In their natural habitat, cats consume prey high in protein with moderate amounts of fat and minimal amounts of carbohydrate (CHO); thus they are metabolically adapted for higher metabolism of proteins and lower utilization of CHO's (starch, not soluble or insoluble fiber) than dogs or other omnivores. Although cats can use CHOs as a source of metabolic energy, they have limited ability to spare protein utilization by using CHOs instead. Nevertheless, commercial diets are formulated with a mixture of animal- and plant derived nutrients, most commonly in dry kibble form that requires CHOs for the expansion and cooking process (rendering), to provide easy-to-use food for domestic cats. And although cats have adjusted to some manufactured diets, the limitations of substituting animal-origin nutrients with plant-origin nutrients in foods formulated for cats are being increasingly realized.
This page and the information reported here is an attempt to describe what it means metabolically and nutritionally to be a strict carnivore, with a focus on differences in nutritional biochemistry of cats. In addition, information is included on probable roles of nutrition in the development of obesity, idiopathic hepatic lipidosis (IHL), inflammatory bowel disease and diabetes mellitus in cats. There are many more feline health issues tied directly to diet. It is my hope to foster a greater understanding of the pet food industry, and the need for a species appropriate diet and the interconnectivity of the same.
The natural diet of cats in the wild is a meat based regimen (eg, rodents, birds, squirrels, rabbits) that contains little CHO; thus, cats are metabolically adapted to preferentially use protein and fat as energy sources. This evolutionary difference in energy metabolism mandates cats to use protein for maintenance of blood glucose concentrations even when the sources of protein in the diet are limiting. The substantial difference in protein requirements between cats and omnivores serves to illustrate this important metabolic distinction. For example, whereas the protein requirement of kittens is 1.5 times that of the young of other species, adult cats require 2 to 3 times more protein in their diet than adults of omnivorous species. The fact that cats have such a greater dietary requirement, compared to dogs, necessitates that cats must have a higher basal requirement for nitrogen (protein) or an increased requirement for essential amino acids. In the case of adult cats, the increased protein requirement is attributable to both; however, the requirement for essential amino acids in kittens is similar to that of the young in other species, so a higher basal requirement for nitrogen is suggested to play the largest role in kittens. Simply put, it’s clear that cats diets must have greater amounts of proteins for their development and maintenance. Several possible reasons exist for the increased need for protein, but the fact that cats depend on protein for energy as well as structural and synthetic purposes is a major component.
Carbohydrates and Fats
It is clear that cats have a greater need than omnivores for protein in their diets. Cats also have several physiologic adaptations that reflect their expected low CHO intake. First cats lack salivary amylase.(An amylase is an enzyme that breaks starch down into sugar) the enzyme that is responsible for initial CHO digestion. In addition, cats also have low activities of intestinal and pancreatic amylase and reduced activities of intestinal disaccharidases (any of a class of sugars (as sucrose) that yields on hydrolysis two monosaccharide molecules (hydrolysis is chemical reaction of a compound with water, usually resulting in the formation of one or more new compounds.) that break down CHOs in the small intestines.
This underscores the cats development as carnivores and the expected amount of grain in their typical diet. These digestive differences mean that high amounts of CHO in diets have a severe negative effect on cats. For example, high amounts of CHO in diets decrease protein digestibility in cats because of a combination of factors, including an increased passage rare, reduction in fecal PH in cats caused by incomplete CHO fermentation in the small intestines that results in increased microbial fermentation in the colon in increased production of organic acids.
These are also very important and different in cats than other omnivores. Cats require increased amounts of many water soluble B vitamins, including Thiamin, Niacin, B6, B12. Cats can synthesize niacin but their dietary requirement is 4 times higher than other carnivores because they have a much higher rate of vitamin catabolism of vitamin precursors. Thiamin deficiency can occur in cats consuming diets high in thiaminase (seafood). Since most water soluble vitamins are not stored a continuous dietary source is required to prevent deficiency.
Vitamins A, D, E, and K are fat-soluble vitamins. Of these cats have special needs for A and D. Vitamin A is found naturally only in animal tissue and must be provided as the active form as cats cannot beta-carotene (plentiful in plants) to retinol (active form of Vitamin A) Cats cant convert it from the plant substances in commercial foods to the active form because their intestines lack the essential enzyme to do so. Vitamin A plays vital roles in vision, bone and muscle growth, reproduction and epithelial tissues. Trying to supplement vitamin A is risky because toxicosis can develop as it is stored in the liver. And commercial food has to keep adding A to the diets to provide it. And the liver keeps on storing it as its added.
Vitamin D is also very much required in a cats diet. Cats can’t meet the metabolic need for vitamin D with dermal photosynthesis like we can (from the sun) because they lack something called (another big word) 7-dehydrocholesterol, which is required for synthesis. Vitamin D is however found in high amounts in the liver and fatty tissue of animals. Cats have always met their need for this through their carnivorous diet. Vitamin D is vital for the development of calcium by intestinal absorption. Deficiency in vitamin D develops slowly. Again commercial foods have to add this supplement. If they over do it, excess amounts of vitamin D can cause hypocalcaemia.
The water needs of cats reflect their early status as a desert dwelling animals and their development as strict carnivores that obtain most of their water from consumption of prey. Cats have a less sensitive response to thirst and dehydration than other omnivores, and they adjust their water intake to the dry matter content of their diet rather than the moisture content. This means cats eating commercial dry foods will consume approximately half the amount of water (in the diet and through drinking) compared to cats eating canned foods. Feeding species appropriate diet or even canned will increase the water intake and urine volume; thus decrease the concentrations of minerals forming in the urine. In older cats that tend to produce urine with a lower concentration, an increase in water consumption becomes even more important to prevent dehydration and prerenal azotemia (kidney disease, brought on eventually by decreased blood flow to the kidneys)
Obesity in Cats
Figures vary, but its estimated up to 33% of cats are overweight or substantially obese. Obesity is the most common nutritional disorder in dogs and cats in the United States. A large number of factors probably contribute to this problem, including sex (intact vs. speutered; male vs. female) age, activity (indoor vs. outdoor) feeding style (meal times or free choice feeding). Neutered males/females require fewer calories (approx. 35-30% less) than sexually intact animals. Many people prefer to feed their cats dry food that is available free choice. Active cats with thin body condition that will self regulate their intake may be fed free choice. However many inactive cats cannot be fed this way, because they tend to overeat as a result of the increased amount of fat and palatability of commercial pet foods. There are a variety of possible explanations for obesity in pet cats including hormonal changes (e.g., neutering), boredom, type of diet (e.g., dry CHO based commercial foods), inactivity (e.g., decreased energy expenditure), or simple overfeeding. However, although a combination of factors is likely to be important in the development of obesity, the role of diet in this problem is being increasingly scrutinized. No matter the cause, fat cats have many health issues, like development of diabetes mellitus, joint problems, lameness, development of lower urinary tract disease, and a range of skin conditions.
A large dietary factor that is a cause of obese cats is the CHO-dense diets. Cats housed indoors and consuming energy-dense, high-starch, dry foods are provided with far more energy than they can effectively use. Any dietary CHO not used for energy is converted and stored as fat. Diets that are restricted for energy (traditional premium, prescription, low-fat, m high-fiber, weight loss diets) might result in weight loss but to the detriment of lean body mass. Most of these diets contain high concentrations of insoluble fiber which increases fecal bulk and volume, increases fecal water loss (risk of dehydration) and has a detrimental effect on nutrient (protein) digestibility.
Inflammatory Bowel Disease
Dietary Intolerance is a non immune clinically important cause of GI tract issues. (vomiting and diarrhea) in cats. It can be caused by a number of substances found in diets formulated for cats, including proteins, and carbohydrate (CHO) source, flavorings, and preservatives and additives like colors and extenders. Removal of the offending substance will cure the problem.
That said, IBD is a idiopathic, inflammatory, immune-mediated disease of the intestinal tract that dietary and immunosuppressive or anti-inflammatory treatments may control., But very little is really understood about IBD. It is likely that it is triggered by an antigenic response to food, bacterial or parasitic antigens in the intestinal immune cells of the GI tract. The mechanism by which this normal inflammatory response becomes aberrant and persistent, ultimately resulting in chronic severe inflammation (IBD), loss of GI function, is unknown.
Direct supportive evidence for a specific role of bacteria in the development of IBD in cats is lacking, but several aspects of digestive physiologic and intestinal microbiologic characteristics of cats suggest a possible role for bacteria in the disease. First, cats have higher concentrations of bacteria in their small intestine, compared to dogs, other omnivores and people. The reason for the increased number in cats is not known, but it may be attributable to their expected carnivorous diet and shorter GI tract. It has been suggested that increased numbers of bacteria in the intestines server to enhance digestion of proteins and fats typically fed to cats. Conversely, diets higher in CHO and fiber my influence bacterial numbers or species, altering the bacterial flora in ways that may include overgrowth of non-beneficial, or pathogenic species. It seems reasonable that due to the natural diet of a cat that is high-protein, moderate-fat, low CHO, the flora and anatomy of the GI tract of cats would be designed to accommodate these diets more readily.
Although a simple change in diet will not solve all of the ills of affected cats, it is reasonable to believe that their lives are influenced by the foods they consume. There is no question that nutrition plays a key role in obesity, diabetes, IHL, and IBD in cats. These problems are complex and involve multiple factors, including genetic and environmental influences as well as the nutritional factors listed above. Nevertheless, pet owners cannot ignore the unique nutritional needs of cats, because unlike omnivores, cats are true obligate carnivores.
Credit to Debra Zoran, DVM, PhD, DACVIM with permission from ACVN
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