The Case Against Dry Diets For Cats
Written by By Karen Becker*, DVM, and Nancy Scanlan**, DVM, CVA | AHVMA Journal on 01 October 2014.
*Natural Pet Animal Hospital & Apawthecary, 711 Almar Parkway, Bourbonnais IL 60914
**Executive Director, AHVM Foundation,404 N Mt Shasta Blvd, Rm B, Mount Shasta CA 96067
Abbreviations:
FIC – feline idiopathic cystitis
JAVMA – Journal of the American Veterinary Medical Association
As an integrative veterinary practitioner with a keen interest in animal nutrition, I believe many of the illnesses seen in domestic cats today are attributable to low quality, biologically inappropriate commercial pet food formulas. Dry food is arguably the worst of all possible options for cats.
Dry diets do not meet the water needs of cats (1).
Today’s housecat evolved as a desert dwelling obligate carnivore designed to get most of the water his body requires from the food he eats. In addition, cats are not as responsive to sensations of thirst or dehydration as other animals, so they do not automatically seek out alternative sources of water when fed a moisture-deficient diet. In general terms, it can be assumed that cats fed dry food diets consume only about half the quantity of water compared to that of cats hunting prey in the wild or cats fed a moisture-dense diet.
Dry diets are high in carbohydrates.
The process of extrusion requires carbohydrates. The feline body is not designed for carbohydrate consumption, as evidenced by a lack of taste receptors for sweet flavors, low rates of glucose uptake in the intestine, no salivary amylase to break down starches, and reduced capacity of pancreatic amylase and intestinal disaccharidases. The only consistent source of carbohydrates cats consume in the wild are pre-digested and obtained from the stomach contents of their prey.
In addition, feline liver enzymes do not upregulate in response to large amounts of carbohydrates in the diet. The activity of a cat’s liver enzymes is designed to handle protein and fat as energy sources, not starches. The majority of carbohydrates ingested by cats are ultimately stored as fat. The livers of cats also do not produce the enzyme necessary to metabolize simple sugars (2).
Dry diets do not provide adequate amounts of highly digestible protein.
Like omnivores, cats need protein for growth and body maintenance. But unlike other animals, felines and other obligate carnivores also utilize protein as a substantial source of energy, which is another unique feature of their nutritional biochemistry. Both kittens and adult cats require significantly more protein than other mammals (6). Whereas other species are able to conserve amino acids to manage a deficit in dietary protein, a cat’s body continues to utilize protein for energy even when there is not enough being supplied in the diet. In addition to their increased protein requirements, cats also have a higher requirement for certain specific amino acids found naturally in animal tissue.
Dry Diets, Urethral Obstruction and Feline Idiopathic Cystitis
A study at The Hebrew University of Jerusalem’s Koret School of Veterinary Medicine evaluated risk factors (among other measures) for urethral obstruction (1).
The cats with urethral obstruction had some interesting predisposing factors in common as compared to the control group. They were significantly younger than the control cats, with most cats between the ages of one and seven years. They were significantly heavier in weight. More were indoor-only cats. And their diets were as follows:
| Type of Diet | Cats with UO | Control Cats |
| Dry food only | 83% | 55% |
| Combination wet and dry | 17% | 42% |
| Wet food only | 0% | 3% |
Another study measured the effect of feeding a specific type of food (designed to increase the acidity of urine) to cats with feline idiopathic cystitis (FIC). Some of the cats in the study were fed a canned formulation of the food and some were fed a dry formulation.
What was striking about this study was that after a year on the canned food, only 11 percent of FIC cats had a recurrence, whereas recurrence in the dry food group was 39 percent (3).
The results of these studies allow for a reasonable suspicion that dry diets play a role in the development of urethral obstruction and idiopathic cystitis in domestic cats. And since wet diets seem to help prevent recurrences of FIC, it also seems reasonable to assume that feeding a wet rather than a dry diet might also help prevent the condition in the first place.
Digestibility of Real Meat vs. Dry Cat Food
In a study published in the Journal of Animal Science, researchers from the University of Illinois evaluated nine adult female domestic shorthair cats to determine the digestibility of three different feline diets — a raw beef-based diet, a cooked beef-based diet and a high-protein extruded dry food diet (4).
Study results suggest that digestibility of protein and fats in both raw meat and cooked meat diets is greater for cats than the digestibility of protein in dry food. Although the dry food had a higher protein content, the protein in the real meat provided better nutrition. According to study authors:
Given the increasing popularity of feeding raw diets and the metabolic differences noted in this experiment, further research focused on the adequacy and safety of raw beef-based diets in domestic cats is justified.
In connection to nutrition in cats, she discusses the role of bacteria in human IBD and suggests bacteria could be involved in feline IBD as well (5). Cats have higher amounts of small bowel bacteria than dogs and humans. While the reason is not known, it could be due to their natural carnivorous diet and shorter digestive tract. In humans, modification of the amount of carbohydrate, protein and fat in a diet had major effects on intestinal bacterial type and number(6). If it is true that increased numbers of bacteria in the gastrointestinal tract help cats digest a biologically appropriate diet, perhaps a diet high in carbohydrates or fiber negatively influences gut flora, allowing for overgrowth of pathogenic bacteria.
Benefits of a Wet Diet for Overweight and Inactive Cats
A study conducted at the University of California-Davis provides evidence of the importance of high moisture content in feline diets, especially in light of the epidemic of overweight and obese cats in the U.S. The purpose of the study was to determine how the water content in food affects the amount cats eat and their body weight(7).
The UC-Davis researchers concluded that consumption of canned food resulted in less food eaten and a decrease in body weight. This was considered a significant finding, since there were no such results when the study cats ate either freeze-dried or dry diets. Body composition (lean body mass, fat body mass, and total body water) did not change, and nutritional content and digestibility were not compromised in cats fed the wet diet.
In the same study researchers conducted palatability studies with a separate group of cats and determined that the canned diets were “greatly preferred” over the freeze- dried and dry diets.
In another study, animal sciences researcher Kelly Swanson and his lab at the University of Illinois were interested in finding a way to maintain healthy body weight in cats, so they decided to test a previously suggested claim that increased meal frequency could help to increase overall physical activity. The goal of their study was to investigate how increasing meal frequency and dietary water content might influence voluntary physical activity in cats of normal body weight(8).
In part one of the study involving changing the frequency of meals, the researchers evaluated the “food anticipatory” activity of the cats, which included any activity in the two hours preceding mealtime. The cats were much more active during those two hours, especially in the group fed four meals per day and the group fed a random number of meals each day.
During the second part of the experiment, which involved a 70 percent hydrated diet (dry cat food with water added one hour before mealtime) fed twice daily, the cats showed an even greater increase in physical activity. Interestingly, peak activity times for this group were after mealtime rather than in anticipation of being fed.
Swanson and his team concluded that increasing the frequency of meals fed per day and offering meals that contained added water encouraged more physical activity among the cats in the study.
Wet Diets and Response to Dietary Changes Later in Life
Cats are famously finicky eaters and tend to develop strong predilections for foods of a specific texture, form and flavor. It is known that cats prefer the diet they were exposed to as kittens, including from weaning to six months of age, as well as the nutrition they were exposed to in utero and while nursing.
In a 2012 study, researchers set out to discover whether kittens fed moist diets, then switched to dry food, would make an easier transition back to moist food than kittens fed dry food from the start(9).
The kittens fed exclusively dry diets for longer than seven months after weaning were not interested in moist diets. This included the cats fed a moist diet during the post-weaning period. For these cats, the less time spent on a dry food diet, the better they maintained their weight when moist food was reintroduced. Four of five cats fed dry food for only seven months maintained their weight on reintroduction of moist foods, compared with two of five cats who maintained weight after 17 months on dry food.
Kittens fed canned foods were more accepting of both raw and canned diets than kittens fed exclusively raw during the post-weaning period. This was probably due to differences in textures. Kittens fed a raw diet post-weaning seem able to distinguish between canned and unprocessed food as adults, unlike cats fed canned food after weaning.
The researchers concluded that periods of feeding exclusively dry food seem to have a significantly negative effect on the ability of cats to accept a transition to a moist diet. The researchers observed, “…any benefit of feeding moist foods early in life seems to be overcome by feeding dry expanded foods for an extended period.”
The study authors were careful to point out that this was a preliminary study, and that larger numbers of cats are needed to verify these results and determine their significance. However, they believe the study supports the benefit of offering dietary variety throughout a cat’s life to preserve adaptability to changes in nutrition that may be necessary or desirable.
What Cats Choose to Eat When Given a Choice
In the most extensive study of macronutrient regulation ever attempted on any carnivore, researchers at the Waltham Centre for Pet Nutrition conducted feeding studies to determine if adult domesticated cats, given a choice, deliberately select food that is biologically appropriate for them (similar to the prey they would hunt and eat if they lived in the wild).
The study suggested that cats have a daily calorie intake target that is equal to 52 percent protein, 36 percent fat and 12 percent carbohydrate(10).
The study cats also:
Had a maximum tolerable level of carbohydrate intake at 25 percent
Exclusively chose high-protein food over high- carbohydrate food
When given the choice of three foods with variable amounts of protein, carbohydrates and fat, mixed them to achieve intake of 52 percent protein, 35 percent fat, and 12.5 percent carbohydrates
When restricted to high-protein diets at over 52 percent protein, were able to tolerate higher levels of protein.
In a follow-up study the group from the Waltham Centre investigated the ability of domestic cats to regulate the macronutrient composition of their diet when provided with foods that differed not only in macronutrient content, but also in texture and moisture content, as typically found in the main forms of commercially manufactured cat foods(11).
The researchers concluded that domestic cats have retained the ability to regulate their nutritional intake to closely match the natural diet of felines in the wild, and this holds true even when they are presented with complex combinations of different wet and dry foods.
Cats are “Hypercarnivores”
Cats have adaptations to the carnivore life which render other types of diets less suitable. An example of that adaptation is the loss of a major enzyme in the liver which is common to omnivores(2).
The Origins of Dry Pet Food
Commercial pet food is a relatively young industry in the U.S. Prior to the 1920s, the only food made exclusively for pets were dog biscuits. During the 1920s and ’30s, the pet food market expanded a bit. Americans with enough money to purchase their pets’ food could find dehydrated, pelleted and canned formulas made from meat and grain mill scraps. But most pets were still fed primarily raw meat and table scraps, in addition to whatever food they hunted for themselves(12).
During the Great Depression the industry saw significant growth, and canned pet food accounted for over 90 percent of the market. Then during World War II, rationing of metal and food made dry pet food popular as an alternative to canned food and table scraps for those who could afford it(12).
After the war, in response to unprecedented consumer demand for processed food, the human food industry created vast quantities of agricultural scraps from grain mills, slaughterhouses and processing plants. Pet food manufacturers immediately understood the unlimited opportunity of human food waste to their industry, enabling the pet food industry to become a convenient receptacle for recycling waste created by the human food industry(12).
In the late 1950s, a U.S. pet food company developed a way to create kibble from superheated vats of meat, fat and grain scraps in a process called extrusion. This new manufacturing process allowed pet food producers to capitalize on the growing popularity of dry pet food. They were able to mass- market the type of food most popular with U.S. pet owners due to its convenience and low cost(13).
Have We Chosen Convenience, Cost and Corporate Interests Over the Health of Cats?
In order for optimal health to occur, animals – including humans — must consume the foods they were designed to eat, and preferably in a whole, fresh and unadulterated form. This is known as species-appropriate nutrition, and study after study demonstrates the biological inappropriateness of dry food for felines.
However, cats are resilient creatures. It often takes years before the significant physical degeneration that occurs from a lifetime of eating the wrong foods becomes noticeable. Because the changes to a cat’s health and vitality brought on by a dry diet are usually neither immediate nor acute, we deceive ourselves into believing convenience pet foods are satisfactory nutrition(14).
For over a half-century, pet cats have been fed inappropriate diets that have kept them alive, but not thriving. And the reality is we have created dozens of generations of animals that suffer from degenerative diseases linked to nutritional deficiencies.
References
Segev G, Livne H, Ranen E, et al. Urethral obstruction in cat: predisposing factors, clinical, clinicopathological characteristics and prognosis. J Feline Med Surg. 2011 Feb;13(2):101-108.
Jiang P, Josue J, Li X, et al. Major taste loss in carnivorous mammals. Proc Natl Acad Sci U S A. 2012 Mar 27;109(13):4956-4961..
Markwell PJ, Buffington CA, Chew DJ, et al. Clinical evaluation of commercially available urinary acidification diets in the management of idiopathic cystitis in cats. J Am Vet Med Assoc. 1999 Feb 1;214(3):361-365.
Kerr KR, Vester Boler BM, Morris CL, et al. Apparent total tract energy and macronutrient digestibility and fecal fermentative end- product concentrations of domestic cats fed extruded, raw beef-based, and cooked beef-based diets. J Anim Sci. 2012 Feb;90(2):515-522.
Zoran DL. The carnivore connection to nutrition in cats, J Am Vet Med Assoc. 2002 Dec 1;221(11):1559-1567.
Fava F, Gitau R, Griffin BA, et al. The type and quantity of dietary fat and carbohydrate alter faecal microbiome and short-chain fatty acid excretion in a metabolic syndrome ‘at-risk’ population. Int J Obes (Lond). 2013 Feb;37(2):216-223.
Wei A, Fascetti AJ, Villaverde C, et al. Effect of water content in a canned food on voluntary food intake and body weight in cats. Am J Vet Res. 2011 Jul;72(7):918-923.
Deng P, Iwazaki E, Suchy SA, et al. Effects of feeding frequency and dietary water content on voluntary physical activity in healthy adult cats. J Anim Sci. 2014 Mar;92(3):1271-1277.
Hamper BA, Rohrbach B, Kirk CA, et al. Effects of early experience on food acceptance in a colony of adult research cats: A preliminary study. J Vet Behav: Clinical Applications and Research January– February, 2012;7(1):27–32.
Hewson-Hughes AK, Hewson-Hughes VL, Miller AT, et al. Geometric analysis of macronutrient selection in the adult domestic cat, Felis catus. J Exp Biol. 2011 Mar 15;214(Pt 6):1039-1051.
Hewson-Hughes AK, Hewson-Hughes VL, Colyer A, et al. Consistent proportional macronutrient intake selected by adult domestic cats (Felis catus) despite variations in macronutrient and moisture content of foods offered. J Comp Physiol B. 2013 May;183(4):525-536.
Pet Food Institute The History of Pet Food http://www. petfoodinstitute.org/?page=HistoryofPetFood Accessed 9/30/2014.
Cowell CS, Stout NP, Brinkman MF, Moser EA, and Crane SW. “History of Pet Food Manufacture in the United States” in Small Animal Clinical Nutrition, 4th ed. Walsworth Publishing Company, 2000, 129.
Pottenger Jr., FM. Pottenger’s Cats: A Study in Nutrition, Price Pottenger Nutrition; 2nd edition (June 1, 1995) Lemon Grove, CA.