Q & A: Should High Protein, Low Carbohydrate Diets Be Fed to All Cats?

I have recently read more and more information about feeding diabetic cats a canned food that contains a low carbohydrate content. By low, I mean a diet that contains less than 10% carbohydrate, ideally closer to 5%.

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?

My Response:

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:
http://www.fda.gov/animalveterinary/resourcesforyou/ucm047113.htm

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.

References:

1. Rucinsky R, Cook A, Haley S, Nelson R, Zoran DL, Poundstone M. AAHA diabetes management guidelines for dogs and cats. Journal of the American Animal Hospital Association 2010; 46:215-24.
2. Myrcha A, Pinowski J. Weights, body composition and caloric value of post-juvenile molting European tree sparrows. Condor 1970;72:175–178.
3. Vondruska JF. The effect of a rat carcass diet on the urinary pH of the cat. Companion Animal Practice 1987;1:5-9.
4. Crissey SD, Slifka KA, Lintzenich BA. Whole body cholesterol, fat, and fatty acid concentrations of mice (Mus domesticus) used as a food source. Journal of Zoo and Wildlife Medicine 1999;30:222-227.
5. Driscoll CA, Clutton-Brock J, Kitchener AC, et al. The Evolution of House Cats: Genetic and archaeological findings hint that wildcats became house cats earlier—and in a different place—than previously thought. Scientific America June 10, 2009.
6. Kirk CA, Debraekeleer J, Armstrong PJ. Normal cats In: Hand MS, Thatcher CD, Remillard RL, et al., eds. Small Animal Clinical Nutrition. 4th Edition ed. Philadelphia: W.B. Saunders, 2000;291-351.
7. MacDonald ML, Rogers QR, Morris JG. Nutrition of the domestic cat, a mammalian carnivore. Annual Review of Nutrition 1984;4:521-562.
8. Morris JG. Idiosyncratic nutrient requirements of cats appear to be diet-induced evolutionary adaptations. Nutrition Research Reviews 2002;15:153-168.
9. Zaghini G, Biagi G. Nutritional peculiarities and diet palatability in the cat. Veterinary Research Communications 2005;29, Suppl 2:39-44
10. Zoran DL. The carnivore connection to nutrition in cats. Journal of the American Veterinary Medical Association 2002;221:1559-1567.
11. Zoran DL, Buffington CA. Effects of nutrition choices and lifestyle changes on the well-being of cats, a carnivore that has moved indoors. Journal of the American Veterinary Medical Association 2011;239:596-606.
12. Laflamme DP. Determining metabolizable energy content in commercial pet foods. Journal of Animal Physiolology and Animal Nutrition (Berlin). 2001; 85:222-230.
13. Thompson A. Ingredients: where pet food starts. Topics in Companion Animal Medicine 2008;23:127-132.