Debunking the myth of L-lysine benefits for cats.

There are certain buzz words in the feline community, and one of these is L-lysine. On many cat groups, as soon as mention is made that kitty has a compromised immune system, someone will shout out "L-lysine!" And while L-lysine has anecdotally been thought to help with feline herpesvirus, it is in fact to be avoided at all costs for cats especially those with suspected FIP, cats infected with the coronavirus and those who are at risk of developing the FIP.

So why L-lysine?

L-lysine has often been touted as a beneficial supplement to control herpesvirus in cats, but this has now been proven to be purely anecdotal, without basis in science. The thinking was due to the fact that L-lysine competes with arginine in the construction of the herpesvirus capsid protein. For a long time, it was argued that L-lysine was effective in treating herpesvirus because the virus itself needs arginine in order to replicate. L-lysine binds to the arginine, making arginine unavailable to the virus and as a result, the virus cannot replicate. However, in recent years, a number of leading research papers have shown L-lysine to be a placebo-type treatment with little to no value when used with cats.

L-lysine and FIP

Cats with FIP, those that have been exposed to and have the coronavirus and those who are at risk of developing FIP should never be given L-lysine. The reason is clear. Arginine is necessary for a good, healthy immune system. As explained above L-lysine prevents arginine from being taken up in the body. But, because FIP is an immune-mediated disease and you want your cat's body to have its full arsenal available, then it is clear that arginine is crucial for a healthy, functioning immune system.

L-lysine is a NO-NO for any FCoV+ Cat

The lack of arginine in a cat's diet may contribute to the development of FIP. However, this is anecdotal and has no clear scientific proof to back it up. Most commercial dry cat foods are based on cereal and are very likely to have low arginine levels. This is where raw feeding, freeze-dried raw foods and treats, or high-quality, grain-free foods are so beneficial as they contain the necessary arginine a cat's body needs.

The role of arginine

Arginine, a major building block in a cat's defensive system, is an amino acid that is essential to maintain a cat's immune system and immune function. Arginine is not only essential for a healthy immune function, but it is also important in the process of urea synthesis. Arginine is also involved in the excretion of ammonia, blood vessel relaxation, and hormone release, making it an important component of your cat's diet.

For the adult cat, an arginine-deprived diet is life-threatening.

Natural sources of arginine

Luckily Mother Nature does look after her own and arginine can be found in a number of food sources which lend themselves well to cats, who are obligate carnivores. Raw meat is one of these and adding a spoonful of this every couple of days to kitty's diet – or even as a treat – will keep those arginine levels up and doing their job. Cats are well looked after as meats are abundant in arginine as are organs. Another rich source of arginine is gelatin. Always remember though when feeding organs that some also contain high levels of other nutrients which in high quantities can be toxic – such as liver which is high in Vit A.
It is always best to double check quantities with a veterinary nutritionist.

Additional resources

For additional information on why L-lysine is now considered of no value in the treatment of cats, you can access the articles at:
• Effects of physiologic concentrations of l-lysine on in vitro replication of feline herpesvirus 1 (AVMA - American Journal of Veterinary Research - 2014)
• lysine supplementation is not effective for the prevention or treatment of feline herpesvirus 1 infection in cats: a systematic review (BCM Veterinary Research - 2015)
• Study Finds L-lysine Does Not Decrease Symptoms of Feline Upper Respiratory Infections (The Conscious Cat - 2016)
• L-lysine for FHV? Researchers Say Don't Bother (Veterinary Practice News - 2016)

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