Why Cats Need Canned Food
By Jean Hofve, DVM
Cats are true carnivores, requiring a meat-based diet for optimal health. Their natural diet is prey such as rodents, lizards, insects, and birds. These prey consist primarily of water, protein and fat, with less than 10% carbohydrate (starch, sugar and fiber) content. Cats are exquisitely adapted to utilize fat and protein for energy. They are not at all like dogs and people, who are adapted to use carbohydrates for energy.
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When feeding our companion cats, the most logical strategy is to feed the diet that most closely mimics the natural prey diet. A homemade diet is an excellent way to accomplish this. Feeding more (or only) canned food is another way--one that is often easier for people to deal with. Canned foods are higher in fat and protein, and lower in carbohydrates, than dry foods. Their high water content increases the cat's overall fluid intake, which keeps the kidneys and bladder healthy. The higher fat contributes to skin and coat health. Because the ingredients are more easily digested and utilized by the cat's body, canned foods produce less solid waste in the litterbox.
Another feature of the cat's natural diet is variety. A hunting cat doesn't one day decide to eat only purple finches! He will eat any small prey he can catch: chickadees, mice, grasshoppers, robins, or rabbits. Likewise, we should feed our cats a variety of foods. Variety keeps cats from becoming finicky and food-addicted, lessens the chance of dietary excess or deficiency of any single nutrient, and may prevent the development of food intolerances, allergies, and inflammatory bowel disease. Feeding the same dry food year after year greatly increases the risk of these problems. With canned food, it is easy to vary the flavors and protein sources.
Dry food typically contains 35-50% carbohydrates, mostly as starch. (The new "grain-free" foods may be as little as 20% carbohydrate). This is necessary because the equipment that makes dry food requires a high-starch, low-fat dough for proper processing. Cereal grains provide an inexpensive and plentiful source of calories, which allows manufacturers to produce foods containing adequate calories at an affordable price. A few dry foods provide less carbohydrates, in some cases substituting starchy vegetables and soy for cereal grains; but they are still heavily processed and just as dehydrating (if not more so) than regular dry food.
Adult cats need 2-3 times more protein than dogs. Yet dry cat foods generally supply only about 1/3 more protein than dry dog foods—about 30-35% in dry cat food compared to 20-26% for the average dry dog food. "Kidney" diets for cats in renal failure are even more restrictive with 26-28% protein (such diets should never be fed to normal cats; they will cause muscle wasting as the cat breaks down its own body for protein). Canned cat foods contain 45-50% protein, and canned kitten foods may contain up to 55% protein. (All percentages calculated on a dry matter basis.)
Cats are attracted to food that has a strong meat or fat flavor. Pet food manufacturers go to great lengths to make their starch-based dry foods palatable to cats. They may coat the kibbles with fat or with "animal digest," a powder made of chemically or enzymatically digested animal by-products. The result may be a cat who overeats, not because he's hungry, but because he loves the taste of the food and doesn't want to stop. (I think we've all been there!)
Dry food is very dehydrating. Our feline friends descend from desert-dwelling wild cats who are well adapted to limited water resources. Their ultra-efficient kidneys are able to extract most of their moisture needs from their prey. However, the end result is that cats have a very low thirst drive, and will not drink water until they are 3-5% dehydrated (a level at which, clinically, a veterinarian would administer fluid therapy). Cats eating only dry food take in only half the moisture of a cat eating only canned food. This chronic dehydration may be a factor in kidney disease, and is known to be a major contributor to bladder disease (crystals, stones, FUS, FLUTD, cystitis). Caution: adding water or milk to dry food does not solve the problem; and the fact that there are always bacteria on the surface of dry food means that adding moisture can result in massive bacterial growth--and a very upset tummy.
The high heat used in processing dry food damages (denatures) the proteins in the food. The resulting unnatural proteins may trigger an immune response that can lead to food allergies and inflammatory bowel disease.
There is increasing evidence that carbohydrates (starches and sugars) in dry food are simply not metabolized well by many, if not most cats. While obesity is caused by many factors, the free-choice feeding of dry food to a relatively inactive cat is a major player. Obese cats are prone to joint problems, liver and kidney disease, and diabetes.
Recent research has shown that high-carbohydrate diets are to blame in most cases of feline diabetes. Many overweight cats are carbohydrate-intolerant, and should be fed low-carbohydrate diets (think "Catkins" diet!). This means canned food. Experts are now recommending canned kitten food as the primary treatment for diabetes. Many diabetic cats can decrease or even eliminate their need for insulin, simply by changing to a high-protein, low-carbohydrate diet. Ultimately, canned food may be even more beneficial as a preventative for this devastating disease.
Overweight cats may greatly benefit from a switch to an all-canned diet. Stick to foods containing 10% or less carbohydrate. Many all life stages and kitten foods fit this requirement. Carbs are usually not listed on the label. However, all you have to do is subtract the other ingredients from 100% to get an estimate of the carb content. Most cats lose weight more efficiently on a canned food than dry food diet. Even though they're often eating more calories, these diets are much better suited to the unique feline metabolism.
If your cat is not used to eating canned food, add it to the diet slowly in small amounts. It is so different in composition from dry food that it may cause tummy upset at first.
If a cat won't eat canned food, it's usually because of a dry food addiction, or because he isn't hungry enough to try something new. Start by putting the cat on a meal-feeding schedule, leaving dry food out only an hour each, morning and night. Once he's accustomed to the schedule, put a little canned food down first. Most cats will be willing to try it at that point. (See "Switching Foods" for more information on why and how to make the change.)
Quality is just as important with canned cat food as any other type of food. See Selecting a Good Commercial Pet Food to learn how to read a label and assess a food's quality for yourself. If possible, buy the food in a larger can, and store leftovers in a glass jar in the refrigerator. Pop-top cans, by-products, and fish flavors of canned cat food have been linked to the development of thyroid disease in cats.
Dry food is a great convenience and may be necessary in some cases when the guardian is gone long hours or cannot feed on a regular schedule. But at least 50% of the diet (preferably 100% if you want to ensure optimum health!) should be a high-protein, high-moisture, low-carb diet such as canned or homemade food. Your cat will be healthier, and while you'll spend a little more on food up front, ultimately you'll save hundreds, if not thousands, on veterinary bills!
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