The scores
Royal Canin Siamese: C (56/100)
Nulo Cat: B (88/100)
A 32-point spread is one of the largest gaps we see in cat food comparisons. It's the difference between a formula built around plant fillers and by-products and one built around named animal proteins. Royal Canin Siamese sits in the middle of C grade, while Nulo lands near the top of B — just two points shy of an A.
How the ingredients compare
Here are the first five ingredients side by side:
Royal Canin Siamese: Chicken By-Product Meal, Wheat Gluten, Corn, Wheat, Brewers Rice
Nulo Cat: Salmon, Turkey Meal, Menhaden Fish Meal, Chicken Meal, Peas
The contrast here is stark. Royal Canin Siamese leads with chicken by-product meal — a low-quality protein source made from parts like necks, feet, and intestines — followed by three grain-based fillers in a row. Nulo leads with whole salmon, followed by three more named animal protein sources before reaching its first non-meat ingredient. Every one of Nulo's top five ingredients contributes meaningful nutrition. Three of Royal Canin's top five are cheap plant fillers that do little for an obligate carnivore.
Where Nulo pulls ahead
Multiple named animal proteins. Salmon, turkey meal, menhaden fish meal, and chicken meal — four distinct animal protein sources in the top five. This provides a diverse amino acid profile that cats, as obligate carnivores, are designed to thrive on.
Grain-free, no corn or wheat. Nulo avoids corn, wheat, and soy entirely. While not all grains are bad, corn and wheat gluten are low-quality fillers that inflate protein numbers without providing the animal-based amino acids cats actually need.
No by-products. Every protein source in Nulo is named and identifiable. No vague "by-product meal" that can vary batch to batch in quality and composition.
High protein for active Siamese. Siamese cats are known for being athletic, vocal, and high-energy. Nulo's protein-dense, meat-first formula is well suited to a breed that burns through calories and needs quality fuel — arguably more appropriate for a Siamese than the breed-specific formula that carries the name. Shop on Amazon →
Where Royal Canin holds its own
L-lysine supplementation. Royal Canin Siamese includes L-lysine, an amino acid that supports immune function. This is a genuinely thoughtful addition — Siamese cats are genetically predisposed to feline herpesvirus (FHV-1), and L-lysine supplementation has been used to help manage outbreaks. It's a legitimate breed-specific consideration that most competitors overlook.
Breed-specific kibble shape. Royal Canin engineers a custom kibble shape designed for the Siamese's long, narrow jaw. Whether this makes a meaningful difference in nutrition is debatable, but some Siamese owners report their cats prefer the narrower kibble.
Beet pulp for fiber. Beet pulp is a moderate-quality fiber source that supports digestive health. It's one of the better non-meat ingredients in the Royal Canin formula and helps with stool quality. Shop on Amazon →
The bottom line
Nulo is the far better food. The 32-point gap tells the story: Nulo delivers named animal proteins, grain-free nutrition, and no by-products, while Royal Canin Siamese buries its first real protein behind wheat gluten and corn. Royal Canin's L-lysine supplementation is a legitimate breed-specific benefit — it's one of the few cases where a breed-targeted formula actually includes something useful beyond marketing. But a single amino acid supplement doesn't rescue a formula where three of the top five ingredients are cheap plant fillers. You can always add an L-lysine supplement to a better food. You can't fix a fundamentally weak ingredient list with one good additive.
Read our full reviews of Royal Canin Siamese and Nulo Cat for the complete ingredient breakdowns.