Whats wrong with cat diets?

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.

dog vs cat teeth

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.

Dental Problems

cat dental xray

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.

Kidney Failure

renal failure foods
From: ISFM consensus guidelines on the diagnosis and management of feline chronic kidney disease

There are two separate issues here.

  1. 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.
  2. 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

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.

Further Reading

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.

Have something to add? Comments (if open) will appear within 24 hours.
By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. Meet his team here.

9 Replies to “Whats wrong with cat diets?”

  1. Your sensible and well-researched advice has been invaluable to me since I got my first dog 2 years ago. But now I find myself with a cat problem and I’m hoping you can give my some advice. My 10 year old cat has just had 2 dental extractions due to resorptive lesions and at least 3 other teeth showed signs of similar past issues . Considering this was his first dental check due to his fear and aggression towards vets and invasive procedures and needing to be put under for even a basic check, I had expected plague build up (which there was surprisingly little of) but was horrified that he had probably been suffering for years with lesions. I am now looking at annual anaesthetic dental checks. I already feed him Hill prescription TD (as I was trying to prolong the inevitable check for as long as possible through diet) and he gets a small amount of human grade kangaroo mince at night. I read your piece about chicken necks and tried him on that a few months ago. He wolved the first one down and since then has barely touched any I offer him. In fact he has always been difficult with boned meat of any kind. I am now wondering if that was because of the pain he was in. I’m also wondering as he has now lost some teeth should I be continuing to try him with the chicken necks? And is there any biscuit out there that will not possibly cause these lesions? Please give me some dietary advice to prevent my cat suffering and needing traumatic dental checks every year.

    1. Hi Jennifer. Your case is very difficult. Yes, I think the reason your cat won’t eat another chicken neck is because the first one caused pain. You can try again (read how here) but pain is a great teacher. If you already used t/d (which generally works the best) then any other dental diet is probably not going to help either. My only other alternative suggestion is to try small bones from other species, but of course I can’t vouch for the safety of these. Many vets believe that the carbohydrate levels in cats food may be contributing to the development of odontoclastic resorptive lesions but evidence is lacking (mostly because nearly all cats eat high carb diets!). Therefore, without any hope of success, you could try my advice for creating a low carb cat diet as a last resort.

  2. My cat was on science for ten years but developed a skin problem when the packaging changed. He seems to be allergic. To the chicken which so many use now. I haVe him o. Fancy feast tuna prawn. Mackerel crab which he likes. No problems but don’t know what to add to make it healthier? Thanks

    1. You’ve already done the hard part by identifying an adverse food reaction. There are plenty of restricted diets available at vets that you could add to the other items to make it a healthier diet overall. Otherwise it’s just trial and error which can be bad news for the cat!

  3. I think your posts are excellent Andrew. The only aspect I don’t agree with is your recommended food products, although they’re products always recommended by vets. Take k/d for example, the by-products I’ll overlook, but we also find CGM, brewers rice, wheat gluten, more corn… which contradicts an obligate carnivore diet.

    Chicken necks are a fantastic supplement, I feed one every other day. Very cheap, nutritious, and natural for a cat to eat. I’m also with you on using human grade mince as opposed to pet mince – safer, and in most cases it’s also cheaper.

    I look forward to reading more of your articles.


    1. Thanks Dave. I agree that the veterinary diets could be made better but with diets like k/d for example, the benefits of prescription foods in kidney disease are well documented. The regular diets I featured, let’s face it, aren’t perfect either but our experience is that they are well-tolerated and provide a good health baseline for most cats. Certainly better than the old days before cat foods!

  4. Completely agree! After a long food trial and process of elimination, we found that one of our cats is allergic to corn, and corn is a common ingredient in the premium food brands. Not surprised at all that cats are developing allergies to grains. Subsequently Wellness Core has been great with a huge variety – they even offer one with only duck and turkey – eliminating seafood and beef.

    Our T1 diabetic cat cannot tolerate any carbohydrate and so he is on an extremely low carb diet. A high protein low carb diet is the only thing to help regulate the blood insulin levels.

    We have also observed that cats may need to eat a little more without the grains filling up their bellies.

    1. Corn is a common culprit of allergies, especially if a cat (or dog) has been fed a single brand of food over an extended period. I rotate foods, which I feel is an excellent way of balancing out a diet and avoiding the development of allergies and intolerances.

      1. Thanks Dave. On this subject although I acknowledge that corn can be an allergen I would respectfully disagree. Most data we are aware of implicate animal proteins at least as much as plant proteins. Our experience with food allergies is that they are rare and unpredictable in the extreme.

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