The scores
Purina ONE: D (52/100)
Royal Canin: D (45/100)
A 7-point gap that keeps both firmly in D territory. Neither formula earns a passing grade, but Purina ONE's slightly higher score reflects a marginally better protein start and a dramatically lower price tag. When both options are below average, the cheaper one wins by default.
How the ingredients compare
Here are the first five ingredients side by side:
Purina ONE: Turkey, Chicken By-Product Meal, Corn Gluten Meal, Soybean Meal, Brewers Rice
Royal Canin: Chicken By-Product Meal, Brewers Rice, Corn, Wheat Gluten, Corn Gluten Meal
Purina ONE starts with turkey - a named, whole animal protein. That's the single biggest difference between these formulas. Royal Canin starts with chicken by-product meal, a rendered product made from organs, necks, and feet. Both formulas then collapse into the same pattern of cheap plant proteins and grain fillers. Corn gluten meal, soybean meal, brewers rice, wheat gluten - different arrangements of the same cost-optimized ingredients. Neither is what an obligate carnivore should be eating.
Where Purina ONE pulls ahead
Named whole meat first. Turkey at position one means the most abundant ingredient is a recognizable animal protein. Royal Canin can't say the same - chicken by-product meal is a rendered, concentrated product, not a whole meat. For an obligate carnivore, starting with real meat matters.
Price. This is the decisive factor. Purina ONE typically costs $1.50-2.00 per pound, while Royal Canin runs $3-4 per pound. Royal Canin charges premium prices for a formula that scores 7 points lower. You're paying more for less. In a matchup where neither food is good, the one that costs half as much is the obvious choice.
Fish meal. Purina ONE includes fish meal further down the ingredient list, providing some additional animal-sourced protein and a small amount of omega-3 fatty acids. It's not much, but it's an animal protein source that Royal Canin's formula lacks. Shop on Amazon →
Where Royal Canin holds its own
Fish oil. Royal Canin includes fish oil, which provides EPA and DHA omega-3 fatty acids - the marine-sourced forms that cats actually need. This is a genuinely useful ingredient for skin, coat, and joint health that Purina ONE doesn't include in this form.
Psyllium seed husk. This soluble fiber supports digestive regularity and hairball management, which is relevant for indoor cats. It's a thoughtful functional ingredient that most budget brands skip.
Research infrastructure. Royal Canin invests heavily in feeding trials and employs board-certified nutritionists. Their formulas are tested in controlled settings, not just formulated on paper. This matters - but it doesn't change what's on the ingredient label.
No caramel color. Purina ONE includes caramel color, a purely cosmetic additive that serves zero nutritional purpose. Royal Canin avoids this unnecessary addition. It's a small point, but it's a real one. Shop on Amazon →
The bottom line
Purina ONE wins this matchup, but calling either food a "winner" is generous. Both earn D grades, both rely heavily on plant proteins and grain fillers, and neither delivers the meat-forward nutrition cats need as obligate carnivores. Purina ONE's advantage is simple: it starts with real turkey and costs about half as much. Royal Canin's fish oil and psyllium husk are nice additions, but they can't justify charging premium prices for a formula that scores lower.
The real recommendation is to skip both. Stepping up to Iams (C/62) costs only slightly more than Purina ONE and adds FOS prebiotics and L-Carnitine. If your budget allows a bit more, Blue Buffalo (B/76) delivers a fundamentally different level of ingredient quality - deboned chicken, chicken meal, no corn, no wheat, no soy. The jump from D to B is the difference between feeding your cat a formula built around cost and one built around nutrition.