Lysine (L-lysine) is an essential amino acid that occurs naturally in foods and cannot be synthesized by the body. It is critical for collagen synthesis, calcium absorption, carnitine production and immune function. In cats, lysine supplementation has historically been recommended for Feline Herpesvirus-1 (FHV-1) infections, but the scientific evidence remains controversial. Lysine may be the limiting amino acid in foods based on plant protein.
| Chemical Name | L-Lysine (2,6-diaminohexanoic acid) |
| Resource Type | Amino Acid (Essential) |
| Function | Protein Synthesis / Collagen / Carnitine Production |
| Dog Need | 0.63% KM (AAFCO min. adult) |
| Cat Needs | 0.83% KM (AAFCO min. adult) |
| Rich Resources | Meat, fish, eggs (animal protein) |
| Discussion Level | low |
Lysine is an essential and nutritionally important amino acid. It is naturally abundant in animal-protein-based foods. Additional lysine supplementation can improve amino acid balance in formulas that rely heavily on plant protein sources.
Why Added?
- Essential amino acid: It cannot be synthesized by the body and must be obtained from the diet.
- Collagen synthesis: Required for hydroxylysine formation and therefore important for connective tissue, skin and joint health
- Carnitine production: Lysine + methionine → carnitine (needed for fatty acid oxidation)
- Calcium absorption: Increases calcium absorption from the intestine
FHV-1 and Lysine Controversy
Lysine supplementation has been recommended for many years in Feline Herpesvirus-1 infections in cats. The theoretical mechanism is that lysine slows viral replication by competitively inhibiting arginine. However 2015 meta-analysis (Bol & Bunnik) did not confirm this effect and even showed that high doses of lysine may negatively affect immunity by reducing arginine levels. Current evidence suggests that lysine supplementation is not effective in treating FHV-1 in cats.
Frequently Asked Questions
What does it mean to see added lysine in food?
Additional lysine supplementation generally indicates a high percentage of plant protein in the food. Since grains and legumes are poor in lysine, free lysine is added to foods based on these sources to ensure amino acid balance. Additional lysine is generally not required in animal protein based foods.
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Bibliography
- NRC (National Research Council). (2006). Nutrient Requirements of Dogs and Cats. National Academies Press.
- Bol, S. & Bunnik, E.M. (2015). Lysine supplementation is not effective for the prevention or treatment of feline herpesvirus 1 infection in cats: a systematic review. BMC Veterinary Research, 11, 284.