Cat Nutrition by Frank Utchen, DVM

Nutritional advice is plentiful these days. Flip on the TV or log on and the ads for what is best to eat—and what medications to take if your will power won't power you to eat that way—are as abundant as the health risks purportedly associated with many of our favorite foods.

So what about our pets? We're not starving for advice here, either.

The thing that veterinary nutritionists have come to realize is that a cat is not just a smaller version of a dog. And while many of the fundamental constituents of cat food are the same as dog food, the proportions of each should be significantly different to meet the special requirements of cats.

For starters, cats evolved eating a normal diet of birds, small mammals, lizards, and bugs. This is a diet high in fats and proteins. Their natural intake of digestible carbohydrates is minimal: although cats do snack on grass when available, which does contain carbohydrates, the carbs in grass are virtually indigestible. This makes cats true "carnivores"—making a living off eating meat. This is different than dogs which are correctly categorized as "omnivores"—they consume their share of meat, but also eat carbohydrates from digestible plant materials.

As a result of this need for different proportions of food ingredients, cats typically maintain their body weight at a healthier level if they are fed diets made primarily of protein and fat, but low in carbohydrates—the kind they are naturally adapted to consuming.

However, what are DRY cat foods primarily made of? You guessed it: carbohydrates. You can't make dry biscuits without flour, and you can't make crunchy dry pet food either. In fact, dry cat foods are often approximately 50% carbohydrate.

We are only starting to appreciate the significance of this. When cats eat high carbohydrate diets they utilize this unexpected source of carbs by burning it for energy, which allows them to store fat for later use.  Unfortunately, cats are extraordinarily good at storing fat when they are fed carbohydrates. In fact, this is a situation that is so pervasive in the domestic cat population that the term "fat cat" has even entered the vernacular. Most real fat cats are eating carbohydrate-rich dry cat food.

Recently, it has been shown that cats fed special canned diets—where carbohydrates are not necessary in the manufacturing process and can be restricted—that are high in fat and protein often lose weight faster than cats on a dry, low-fat, carbohydrate-rich food.

At least part of this has to do with the same reason the Atkins diet and similar low-carb approaches work for so many people. When eating carbohydrate-rich diets, people and cats tend to use the carbohydrates as their source for energy, and therefore don't have to burn their own body fat. In fact, eating enough carbohydrates will mean that even the small amount of fat in low fat diets will be stored (as body fat) for later use rather than burned now.

Of course, waiting long enough between carbohydrate meals may require the body to burn fat for energy in the interim, but for cats eating dry food this does not normally seem to be the case. Most cats fed dry food have it available all day long and can snack on it frequently, which they do. This is not unlike a person snacking on chips, cookies, or other carbohydrate sources, like sugar-loaded soda, all day: by continually providing the body with small (or large) amounts of carbohydrates, the body has no reason to dip into its fat reserves. As a result, many of our cats stay chubby.

The heaviest cat I've seen in practice? Believe it or not, I have seen one cat that weighed 35 lbs. I've also treated a 29 lb. cat.

So how can you best provide for Fluffy? If Fluffy is overweight (ask your veterinarian to level with you on this), consider a switch to a high quality canned food. Specifically, there are special canned prescription diets that are specially formulated to maximize this effect. And if you can handle the strained grimaces of your friends, you can even tell them your cat is on the Catkins Diet.

Now, before you cry "fowl" that you thought dry cat food helped keep your cat's teeth cleaner, let me acknowledge that fact for you. Not only will dry food help keep your cat's teeth cleaner, it is also less expensive, and for better or for worse (as mentioned above) you can leave dry food out all day for your cat. And to make your decision even more difficult, there are special dry foods formulated to keep a cat's teeth even cleaner than regular dry foods do.

So, given that every cat is an individual with their own set of health issues, what is right for your cat? There is no single answer for all cats. This column is not necessarily a ringing endorsement for a switch from dry food to canned food, but rather an explanation of what we currently know about the benefits and disadvantages of each form.

In my opinion, cats with clean teeth but with weight issues should try the canned prescription diets that are low in carbohydrates and higher in fat and protein. Thinner cats, but those whose teeth require frequent cleaning, may be better off eating one of the tartar-control dry foods. Cats with neither issue should be fed the prescription canned foods so they don't become overweight, but in these cases even more emphasis must be placed on brushing their teeth regularly (that's a topic for another column).

My belief is that over time we will find that most cats who are fed a lower carbohydrate, canned food—which is similar to what closely-related cat species have been eating for millions of years—will result in thinner, healthier cats.

Ask your veterinarian for his or her honest advice. Most of us won't "sugar-coat" our answers.