Gazette Vet: Canned vs. Dry?

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By John Andersen, DVM

Cats are incredible creatures and wonderful pets. Intelligent, independent, always aware and studious, amazing hunters, agile jumpers and climbers, nighttime stalkers. Their talents are many, yet they are humble and gentle by nature. Bringing a cat into your home is typically a very welcome experience. Some people will claim they are not “cat people,” but I would argue that they’ve just never had a cat.

A common saying we have in veterinary medicine is that “cats are not small dogs,” and this definitely holds true. Though there are many similarities between the two, they are completely different species, having quite different behaviors and body systems that lead to unique health needs and problems.

One of the most common health issues we see with cats is simply a cat-diet mismatch. I don’t ever really recommend a particular brand of food, and I tread lightly on diet discussions if I see a cat that is healthy across the board. However, the fact remains that most Americans feed their cats a diet that is not really optimum for cats: dry cat food.

I need to preface this point by saying that all of our cats are spoiled and will certainly never die of starvation or malnutrition on a dry food diet. And despite it not being ideal (explained below), many cats tolerate it just fine. So this column is really more to educate on some specific cat nutritional needs and nutrition-related problems, not so much to convince everyone to change their cat’s diet.

Let’s start by reviewing the original cat model: wildcats. Cats are obligate carnivores—their natural design was built for hunting and eating mostly small rodents. On average, small rodents consist of 55 percent protein, 45 percent fat, and 2 percent carbohydrate. Rodents are also made of approximately 60-70 percent water. Without a doubt, this is the food source that cats are designed to eat. Thus, it would make sense that if we were making commercial cat food, we would create a diet that was near these ratios, right?

The vast majority of dry foods have a profile of 35 percent protein, 15 percent fat, a whopping 40-50 percent carbohydrate, and just 5 percent water. Compare this to the rodent. Pretty different!

So why is dry food the standard diet we feed our cats, and is this okay? Canned food on the other hand has an average profile of 40-50 percent protein, 40-50 percent fat, 10 percent or less carbs, and 70 percent water. Much better.

Dry food has many advantages over canned food that make it so popular as a diet choice for your cat. Dry food is less expensive, less smelly, less messy, requires less packaging, and can be left out all day. From a convenience standpoint, it is easy to see why dry food would seem preferable.

Many cats seem to do quite well on dry food-only diets, however there are many diseases that we now know are associated with feeding a dry-only diet. So much so that it is now hard for me to recommend that anyone feed cats dry food exclusively. The diseases most associated with dry food diets are obesity, lower urinary tract (bladder) disease, diabetes, and inflammatory bowel disease.

Obesity is probably the most common of these and stems from the fact that all those additional carbohydrates cats are consuming in dry foods go right into fat storage. Indoor cats are already predisposed to obesity from inactivity, but throw in a 50 percent carbohydrate diet for a species that only needs two percent carbs and you’ve got a recipe for obesity. We regularly see obese cats lose weight when their owners stop the dry food and feed 100 percent canned food.

Bladder problems are also very common and dry food is mostly to blame. Bladder inflammation, which looks just like a bladder infection (frequent urination, peeing outside of the litter box, blood in urine) happens when the urine is overly concentrated or when crystals form in the urine and irritate the bladder lining. These are both caused by dry foods because of the lack of water and the fact that the high carbohydrate concentration causes an elevated urine pH. Struvite crystals, the number one cause of bladder inflammation, only happen in neutral to slightly alkaline pH, which is often associated with dry food. The extra water and higher protein in canned foods causes more dilute urine with a more natural acidic pH and often solves this problem. We often see male cats present to us on an emergency basis because they suddenly cannot pee—their urethra has been obstructed by a clump of crystals, white cells, and mucus. This is a serious, life-threatening problem, but is typically totally preventable by feeding a canned food diet.

Diabetes is another common disease in cats that is largely diet based. Just like in people, diabetes is often associated with obesity, and the excessive carbohydrate load in dry food is constantly forcing insulin secretion throughout the cat’s life. Eventually, they develop insulin resistance and become diabetic, which is a very frustrating disease to treat.

Managing diabetics is where I have become a true believer in the power of canned cat foods. The vast majority of diabetic cats are obese cats eating primarily dry food. I can typically cure these cats of their diabetes by switching them to a 100 percent canned food diet, along with a short course of insulin to get them back on track. In a short period of time, we can stop the insulin and get good long-term control by canned food alone. That is pretty convincing, if you ask me.

Last, chronic gastrointestinal problems are often associated with dry foods, as the feline intestinal tract was not developed to handle such a high carbohydrate load. Some cases of chronic vomiting and/or diarrhea will resolve by switching to a low carb/high protein diet, i.e. canned cat food.

Talk to your veterinarian about whether or not you should change your cat’s food. This seemingly simple nutritional information is surprisingly relatively new. I graduated from veterinary school in 2002 and there was no information or recommendation about canned vs. dry foods. But you can always go back to the way animals were designed and usually the answers lie there.

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