By Jean Hofve, DVM
Cats are true carnivores, requiring a meat-based diet for optimal health. Their natural diet is prey such as rodents, rabbits, 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 protein and fat for energy. They are not at all like dogs and people, who can use carbohydrates directly for energy. Cats lack the metabolic pathway that we and dogs use for processing carbohydrates; in cats, excess carbs end up as body fat. Given that more than 53% of U.S. cats are now overweight or obese, the most commonly fed diets–dry kibble–are clearly not doing cats much good! Add to that a rising rate of feline diabetes–also considered by many to be caused by dry food–and it’s clear that we need to take a different approach to feline nutrition!
Dry food typically contains up to 50% carbohydrate, mostly as starch (the remainder is fiber). “Grain-free” foods may contain just as much carbohydrate in the form of starchy vegetables. “Low carb” dry foods may be as little as 20% carbohydrate, but the higher protein and fat make them higher in calories, and even more dehydrating. This is necessary because the equipment that makes dry food requires a high-starch, low-fat dough for proper processing. Cereal grains and vegetable starches provide an inexpensive and plentiful source of calories, which allows manufacturers to produce foods containing adequate calories at an affordable price.
Another prominent feature of the cat’s natural diet is a high water content. Prey animals like rodents, lizards, and birds contain 65-70% water. Dry diets containing 10% water are completely unnatural to the cat.
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 up to 3% dehydrated (a level at which, clinically, a veterinarian would administer intravenous fluid therapy). Cats eating only dry food take in just 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.
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. Raw, frozen, and reconstituted freeze-dried or dehydrated foods also work very well. However, many people aren’t able to go with completely homemade, and commercial products can be expensive.
Feeding more (or only) canned food is another way–one that is often easier for people to deal with. Canned foods are higher in 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. 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, whether it be mice, voles, pigeons, grasshoppers, geckos, or rabbits. Likewise, we should feed our cats a variety of foods. Variety keeps cats from becoming finicky and food-addicted, reduces 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 kibble day in and day out, year after year, greatly increases the risk of these problems. Cats get bored with the same food all the time–wouldn’t you? With canned food, it’s easy to vary the brands, flavors and protein sources.
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 the protein it needs for vital functions).
Canned cat foods contain 45-50% protein, and canned kitten foods may contain up to 55% protein 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.
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. 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 percentages of the other listed ingredients from 100% to get a ballpark estimate of the carb content.
Most cats lose weight more efficiently on a canned food than dry food diet. 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 this article to learn how to read a label and assess a food’s quality for yourself. 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 a very few cases. 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, raw, 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!