Do you agree? If so, what about feeding normal cats? Should I recommend a canned cat food that has less than 10% carbohydrate for most cats in general? Would this help reduce the frequency of fat or diabetic cats or both in my practice?
This is a very controversial area, but I do believe that diabetic cats should be fed a low carbohydrate, high protein diet and most endocrinologists agree (1). Lowering the carbohydrate level in cats with diabetes mellitus improves their insulin sensitivity and makes them easier to regulate. And some cats will even go into diabetic remission on the low-carbohydrate diets.
From there, I don't think it's much of a leap to ask —why do we wait until cats become diabetic to feed them differently? To me, it makes a great deal of sense to feed normal cats a diet composition close to what they would be getting in the wild. That would be a diet composed of approximately 50-60% protein, 5-10% carbohydrates, and 30-50% fat (2-4).
A Cat's Natural Diet in the Wild
Cats are true obligate carnivores (5-11). This means they must eat meat to survive; cats cannot be vegetarians. Put another way, cats are meant to consume animal-based proteins (meat), not plant-based proteins (grains).
Why should we pay attention to what a cat would eat in the wild? Because cats, at least compared to dogs, really aren't that domesticated as far as their nutritional needs are concerned (5). Domestication has changed feline metabolism very little. Historically, we have valued them for their hunting abilities (controlling rodents). It is only recently that we have tried to feed cats a processed, carbohydrate-filled diet. It is no coincidence that this same period also exhibited a dramatic increase in obesity and a multitude of diseases, including diabetes and hyperthyroidism (10,11).
In the wild, cats eat whole, raw prey. Their diet includes small rodents (e.g, mice, rats), rabbits, birds, insects, and amphibians (5-10,11). They usually eat the whole animal, including the meat, bones, brains, and organs. Their systems are uniquely set up to metabolize this diet which is high in moisture, high in protein, and very low in carbohydrates. Because this is the diet they have relied upon for tens of thousands of years, they do not have the ability to process carbohydrates very efficiently. Cats get most of their energy requirements from the glucose their livers process from protein, not carbohydrates (7,8,10).
Of course, cats in the wild do not eat corn, soybeans, rice, or grains as part of their daily meal. But that's exactly what we are asking our cats to eat when we feed them many of the commercial foods we recommend every day — why would we continue to feed cats plant-based diets better suited for omnivores?
Determining the Composition of Cat Food Diets
Composition refers to the breakdown of the 3 basic food components — protein, fats, and carbohydrates.
The most accurate way to evaluate pets foods and their composition is to consider the calories or metabolizable energy (ME) that come from the protein, fat, and carbohydrate fractions (12). This allows us to compare various diets without worrying about their different water (moisture) levels. I find it very confusing to calculate the value of an individual nutrients when expressed as a percentage of food weight (as fed) or as a percentage of dry matter (dry matter basis)
Check out this website (http://binkyspage.tripod.com/foodfaq.html), which gives you a breakdown of the composition of the various prescription and over-the-counter diets. Remember that we'd like a diet that provides less than 10% of calories from carbohydrates and around 50% of calories from protein. It turns out that many of the over-the-counter diets have a better composition of protein and carbohydrates than you might have thought — even better than many of the more expensive prescription diets.
When looking at caloric distribution (instead of food weight), you can compare canned and dry foods on a fairly equal level. Notice that the composition of almost all dry food cat diets are much too high in carbohydrates and most are too low in protein content. That is why I believe it's best to limit the amount of dry food that is fed to cats, or even better, not feed dry food at all.
The Cat Food Ingredient List
Once we find a diet with the composition that is acceptable, we also have to look at the ingredient list of the food (13). Not all of the proteins in cat foods are equal in quality. Remember that quality meat is the best ingredient in a food and that meat byproducts is a close second; but vegetable and grains may supply a less bioavailable form of protein for cats.
All ingredients are required to be listed in order of predominance by weight. The weights of ingredients are determined as they are added in the formulation, including their inherent water content. This latter fact is important when evaluating relative quantity claims, especially when ingredients of different moisture contents are compared.
Look at the ingredient list supplied by the manufacturer. If the first ingredient is meat, the label should say so. If the first ingredient is a "byproduct" (unrendered parts of an animal left over after slaughter) remember this can include heads, feet, intestines, feathers, and egg shells. Even thought this may not be very pleasing to think about eating yourself, remember that cats do not share in people's aesthetic concerns about the source and composition of their food.
Cat foods with meat byproducts as a first ingredient are still much better than foods that lists grains (e.g., corn, corn gluten meal, or rice) as a first ingredient. The main ingredients in a carnivore's diet shouldn't be grain, it should be animal protein.
For more information on understanding labels, visit the FDA's website on interpreting pet food labels:
Feeding Your Cat: The Bottom Line
Cats have gone from frequent consumption of small meals that consisted of animals they could catch and kill, to consumption of prepared diets of human choosing, which are often available in excessive amounts. In addition, the composition of the diets fed do not match the high protein/ low carbohydrate ratio than is found in wild birds, insects, and small rodents.
As a result, there is increasing evidence that many of the chronic health problems of domestic cats, including obesity, diabetes, and probably hyperthyroidism, are directly or indirectly related to nutrition or lifestyle changes that have been imposed on them by their owners (10, 11).
Let's use some common sense and feed cats foods that are closer in composition to what they are best designed to eat.
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