Unlike their canine counterparts, who can successfully exist as omnivores (and even survive such an extreme diet as to consume only a vegetarian or vegan diet), cats are strictly a truly carnivorous species. In fact, denying them animal-based proteins is likely to cause severe health issues and malnourishment; this therefore, is never a safe option for any cat. But why is this the case and how has this come about?
The definition of an obligate carnivore is an animal who must eat meat out of necessity. In conjunction with this, is the need to eat meat to provide certain vital essential nutrients (which cannot be manufactured at all / or at sufficient quantities), naturally within the body.
Our cats’ unique and specific need for a high quantity of dietary protein within their food intake is thought to be a result of their evolutionary adaptation for food availability from animal sources. Cats have evolved to consume a diet rich in prey, caught immediately after hunting. Such prey are a high protein source, with a low to moderate level of fat and contain only a minimal carbohydrate content. Cats were therefore historically metabolically adapted for higher protein catabolism (breaking them down) and an associated lower carbohydrate utilisation. To aid such swift digestion of protein and fat, a cat’s digestive tract is short compared to other species.
A cat’s dietary requirement for protein (at a minimum of 26% of its intake), is much higher than that of either a dog (12%) or humans (8%). Through time, cats have evolved many unique anatomical, physiological, metabolic and behavioural characteristics; these differences are consistent with eating such a strictly carnivorous diet.
Cats are actually able to eat diets containing up to 70% protein. And as mentioned above, and conversely are poorly developed to enable efficient carbohydrate digestion. As a profession, we have learnt and focused on such elements of feline nutrition over the past few years; particularly when treating certain conditions such as diabetes mellitus. Furthermore, a rise in popularity of high protein foods has become apparent for those owners attempting to feed their cats a more “natural” diet.
Due to their long evolutionary history of meat eating, cats cannot easily process nutrients from plants in the same way that other species do. Plant based nutrients such as sugars, starches and carbohydrates are not well digested by cats. It can lead to certain issues and concerns.
Certain amino acids (the building blocks of protein), many vitamins and some omega fatty acids are all essential to a healthy cat and can only be found within meat. Vital amino acids include taurine, arginine and cysteine. A sustained deficiency in taurine, for example, can lead to retinal degeneration (and consequentially blindness), dilated cardiomyopathy (and likely associated heart failure) and reproductive issues (a lack of fertility, abnormal development in kittens etc.). Without meat protein in their diets, cats would fail to obtain certain nutrients. They could not sustain wellbeing and good health.
A key consideration is that cats have a unique metabolism with respect to many aspects of their protein use, degradation (breakdown) and disposal. Having a large obligate daily need for sufficient protein in their diets, cats are interesting in that they are unable to down regulate their protein conversion to energy (as might other species). This conversion is also unable to be slowed even during periods of starvation. It is at such times that cats can develop harsh metabolic and systemic consequences.
Cats essentially also lack metabolic flexibility because they use protein (and fat) as their primary energy sources. They cannot downregulate the urea cycle enzymes associated with protein use, and neither can slow their own proteolysis (protein breakdown).
Protein is also the main and primary macronutrient responsible for the maintenance of muscle mass in cats. Prolonged starvation or inadequate protein intake can both cause abnormalities such as reduced immune function.
Diets high in protein are also naturally beneficial to cats in that they contain a higher percentage of total water and thereby increase water intake. (Which can be beneficial for a variety of feline medical conditions).
Cats are also unique in that over the process of their evolution, they have lost the ability to synthesise various vitamins endogenously themselves. Certain metabolic pathways have become non-functional as they have been historically unused and unnecessary (the nutrients being readily provided in meat). Cats therefore rely on adequate active sources of vitamins A, D and B12 (amongst others) in their food. And as such, meat must be present in their diet in order to provide these.
Can these nutrients be provided synthetically?
Probably, yes. Most of the proteins in particular can be either purified or synthesised chemically. In fact, there is a lot of research into synthetic diets for cats. Although much of it is unpublished and non-peer reviewed, being performed by for-profit pet food manufacturers and not released for scrutiny. In addition, there are some legal issues. For example, it is actually illegal to feed plant-based vitamin D2 to animals in the UK. This is because it is not an authorised additive (it is also less effective than animal-based vitamin D3).
There is some research into using UV-irradiated algae to generate truly vegan vitamin D3, or into harvesting the rare reindeer lichen for the small amounts of vitamin D3 in it (although the sustainability of these approaches leaves a great deal to be desired). Currently, there is no published data on the commercial viability of these plans, even if some vegan manufacturers claim to be using them.
Overall, though, yes, it probably can be done. Although how expensive and how environmentally friendly it would be to produce a properly balanced diet using entirely chemically synthesised animal protein is another argument. Certainly, there are anecdotal reports of cats on vegan diets doing well; although there are a lot of case studies where there have been complications.
Overall, though, the current best-evidence is that most vegan diets have significant nutritional imbalances. So we would not recommend them at this time given that meat-based diets are proven, safe and effective.
And so, the best food is?
All commercially available cat food should provide the correct and balanced nutrients for your cat. It is prudent to feed your kitten, adult or senior cat with an appropriate “life-stage” diet. And there may be additional considerations such as whether your cat is neutered/entire, indoor based or active outdoors. Of course, some food manufacturers will use higher quality components than others and the protein/carbohydrate composition of a food may vary according to price. Higher protein foods usually translate into higher percentage meat content foods.
A good “rule of thumb” recommendation is to ensure that animal proteins form at least 29% of the diet. The higher priced range end of the markets, unsurprisingly, will exceed this minimal protein level. (And concurrently, will not contain a high percentage of carbohydrates).
Due to a cat’s obligate need for protein and many other nutrients, the successful provision of a complete and balanced home cooked diet is unlikely to be achieved and is not to be recommended except under strict guidance from a qualified veterinary nutritionist. If you have questions or concerns about your individual cat’s diet, then please speak to your veterinary surgeon for advice.