Updated November 29, 2020
There’s something no-one in the cat food industry wants to talk about. Up to now, neither have I. It’s not quite a secret but it’s certainly an unpleasant truth we like to avoid.
It’s about the amount of carbohydrate in cat diets.
Previously I discussed grain free and low carbohydrate foods for dogs. My view is that once the arguments are stripped away and we look at the evidence, it’s not unnatural for dogs to eat carbohydrate-rich food.
The Difference Between Cat And Dog Diets
Cats are different. Cats don’t taste ‘sweet’ and they don’t digest starches and sugars as well as dogs. They appear to be poorly adapted to high carbohydrate diets.
Remember this picture of cat and dog teeth? I used it to show that dogs are adapted to a wider food choice, and I presented evidence that dogs have adapted to a similar diet to early human companions. Now it’s time to make the opposite point: cats are obligate carnivores who have undergone very little adaptation since their domestication. They are specialist ‘whole prey’ feeders.
For example, look at the results of this study into cat diet selection.
A group of researchers in 2011 looked at how cats choose foods under different fat, protein and carbohydrate levels. Here’s what they found:
- Using dry foods, “cats were attempting to minimise carbohydrate intake but were unable to select less than 26% of their calorie intake from carbohydrate, as this was the lowest percentage available in the diets offered”.
- Cats appeared to have a “maximum tolerable level (ceiling)” of carbohydrate and would attempt to not exceed this.
- The target energy intake appears to be 52% protein, 36% fat and 12% carbohydrate.
Now, these numbers aren’t random. They are almost exactly the same as the composition of whole adult rats and mice.
Why are cat foods high in carbohydrates?
Generally speaking, nearly all dry cat foods have carbohydrate levels over 30%. It’s not just because they are cheap.
Carbohydrates seem to be an essential ingredient in the manufacture of cat biscuits. Fats and proteins just won’t stick together in dry clumps without a binder. So whereas dry foods typically have high carbohydrate levels, wet foods can be lower. Not always, though.
Are Modern Cat Foods Harmful?
Does it matter if we feed cats a high carb diet? It’s very important not to be a scaremonger. Most cats are living long and healthy lives and have no obvious effects from their high carbohydrate, dry diets. Let’s look at a few of the suspected and real problems.
I don’t like the amount of carbohydrate in dry cat foods, but studies show it doesn’t seem to be causing diabetes. The big risk factors are, unsurprisingly, inactivity and obesity. That said, if my cat became diabetic, I’d certainly be exploring low carb diets for cats.
The type of diet is not known to be one of the risk factors for obesity in cats. Far more important is what we call ‘free feeding’ where cats just graze at the food bowl when they want. In other words, dry biscuits do get cats fat, but only due to encouraging bad feeding habits. There are many benefits of meal feeding cats you can explore by following the link.
Cystitis and Urinary Problems
This is very important for some cats, but this time due to moisture, not carbs. There’s no doubt that dry foods increase the risk of cystitis and urinary blockages, probably due to the lower water intake. If you visit my page on cystitis in cats you’ll see I strongly recommend a wet-only diet for these poor kitties, and ideally for everyone.
Do carbohydrates cause dental problems in cats? It’s a reasonable suspicion but inexplicably has never been studied. If studies in dogs are any guide, the reverse could be true, but then dogs get different problems. My suspicion is that the odontoclastic resorptive lesions of cats will end up being more common with carbs. In the meantime, it’s clear that good dental care in cats is all about textured foods and tooth brushing.
There are two separate issues here.
- Do dry diets cause kidney problems in cats? There’s no evidence so it’s hard to say. My guess is no, based on the many studies that have looked.
- Are carb-rich renal diets beneficial to cats with kidney disease? That’s a clear yes, as you can see from the table. However, it is prudent to feed these in wet form rather than dry purely for the water intake.
Food allergies certainly exist to some foods, and it’s also true that changing to a natural diet will fix some of these. What’s not clear is whether they are any more likely on commercial foods. Judging by food allergy data, that could be true for foods containing fish.
Food intolerances are another concern. I had a cat once who could not eat dry biscuits without diarrhoea and I have since seen others. I suspect that this is a carbohydrate intolerance. If you read my page on cat diarrhoea, you will see that one of my interventions is a low-carb diet trial.
So what is the best cat diet?
PLEASE don’t change your cat’s diet without consulting your vet, especially if they are young, old, pregnant or have problems like kidney disease.
Grain-free cat foods usually aren’t the answer if all they do is switch the carbohydrate source to other sources like potato. What we need are lower carbohydrate diets that are balanced for all the major and minor nutrients.
To answer the question visit this page for advice on making cat food & creating a low carb diet.
We also have a companion page which lets you calculate the carbohydrate levels in your cat food.
Hewson-Hughes, A. K., Hewson-Hughes, V. L., Miller, A. T., Hall, S. R., Simpson, S. J., & Raubenheimer, D. (2011). Geometric analysis of macronutrient selection in the adult domestic cat, Felis catus. The Journal of experimental biology, 214(6), 1039-1051.
Dierenfeld, E. S., Alcorn, H. L., & Jacobsen, K. L. (2002). Nutrient composition of whole vertebrate prey (excluding fish) fed in zoos. US Department of Agriculture, Agricultural Research Service, National Agricultural Library, Animal Welfare Information Center.
Rand, J. S., Fleeman, L. M., Farrow, H. A., Appleton, D. J., & Lederer, R. (2004). Canine and feline diabetes mellitus: nature or nurture?. The Journal of nutrition, 134(8), 2072S-2080S.
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By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. These articles are from a series regularly posted on email and Twitter. Subscribe via email here to never miss a story!