Comparing the prices of cat and dog food is dispiriting for the cat owner. Cat food is much more expensive…but there are good reasons for this.

Cats can safely pinch the odd dry dog food kibble or eat the odd emergency ration, but dogs and cats have very different nutritional needs. If a cat is fed on dog food regularly, they do not receive all the nutrients they need to stay healthy and will soon become unwell.

The Pet Food Manufacturers Association (PFMA) state that cats require 41 essential nutrients compared to 37 in the dog. They are also less able to digest plant material because of their shorter intestine. The length of the intestine determines the surface area for absorption of nutrients.

Cats and dogs have evolved to eat different diets 

Cats are obligate carnivores, this means that they require animal-based protein and fat. Whereas dogs are omnivores like us so they can derive their nutrients from a mixed diet of meat, vegetables and sources of carbohydrates. Cats need animal protein because they cannot make certain essential nutrients from plant-based protein. 

Although dogs can synthesise the two proteins, taurine (albeit not very efficiently) and arginine, cats can not. 

Taurine deficiency causes serious disease

Without taurine cats develop a disease of their heart wall which causes heart failure. The disease is called dilated cardiomyopathy, this occurs when the heart wall stretches so it cannot pump effectively. Taurine deficiency can also cause absorption problems in the digestive tract and loss of vision. All commercially prepared cat diets are tested for adequate taurine and supplemented if the levels are not high enough. 

The Arginine Problem

Arginine deficiency is also potentially dangerous – a single meal deficient in this nutrient can cause brain damage and even death (1).

Protein Requirements

Obligate carnivores also derive most of their energy from the digestion of protein and fat, rather than carbohydrate. Cat foods should contain 30-34% protein and 15-20% fats (2), leaving little room for digestible carbohydrates such as rice and corn. Carbohydrates are not necessary for cats, they are only added to lower production costs when there adequate protein and fat are present.

However, dogs can derive energy more effectively from carbohydrates, so they only need a 18-26% protein diet and the level of fat in cat food is often too high for them. Dogs that eat a lot of cat food can get gastrointestinal upsets and pancreatitis. 

Protein and Life-stage 

The high protein requirement in the feline diet is particularly important for the rapidly growing kitten and the senior cat who needs to maintain muscle health. Feeding dog food makes cats unwell but the effects would be especially marked at these high demand life stages. Kittens and old cats need a ready supply of easily digested protein to stay healthy. 

Picky Eaters?

As a result of the high protein, high fat content cat food is very palatable. This is important as cats can be picky eaters. They have less incentive to eat as they have far fewer taste receptors than humans or dogs. We have over 9000 taste receptors, dogs 1700 and cats only 470. Although cats like to hunt, scavenge and explore new foods, it is unusual for them to eat the much blander dog foods. Cats don’t have taste receptors that detect sweet tastes at all. 

Fatty Acid Requirements

Cats can’t make one specific essential fatty acid, arachidonic acid. This is important for organ function and skin health. Like taurine and arginine, dogs can make it themselves from other components of their diet. Arachidonic acid is also added to cat food. 


Vitamin requirements also vary between our pet species. Vitamin A is essential for vision, muscle function and coat quality. Cats need higher levels than dog food, a cat fed dog food would be severely deficient. Cats cannot turn the protein tryptophan into niacin or Vitamin B3. So, they require high niacin levels. Plants are low in niacin so this is another requirement must be met with animal-based protein. Signs of niacin deficiency can appear non-specific. They include poor appetite, retarded growth, weakness and gastrointestinal disorders.

The PFMA suggest feeding a species-specific diet formulated for your cat’s life stage

If your cat will eat dog food it is fine to replace the odd meal when you run out of cat food but only as a temporary measure. Dog food is not toxic or unsafe – it is just nutritionally inadequate. Your dog will probably confirm the higher value of cat food by attempting to steal it at any available opportunity…!

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  1. James G. Morris, Quinton R. Rogers (1978) Arginine: An Essential Amino Acid for the Cat, The Journal of Nutrition, Volume 108, Issue 12, December 1978, Pages 1944–1953
  2. Zaghini G and Biago G. Nutritional peculiarities and diet palatability in the cat. (2005). Veterinary Research Communications 29:39-44