The scores
Diamond Naturals Adult Chicken & Rice: B (78/100) — Above average. Two named chicken proteins, whole grains, probiotics, superfoods, and dual omega-3 sources.
Purina ONE SmartBlend Chicken & Rice: C (58/100) — Average. Real chicken first, but corn, soy, and by-product meal fill in behind it.
How the ingredients compare
The top five ingredients tell the story:
Diamond Naturals: Chicken, Chicken Meal, Whole Grain Brown Rice, Cracked Pearled Barley, White Rice
Purina ONE: Chicken, Rice Flour, Corn Protein Meal, Whole Grain Corn, Chicken By-Product Meal
Both start with chicken, which is good. But after that first ingredient, the formulas diverge sharply. Diamond Naturals follows with chicken meal — a concentrated protein source with roughly 3x the protein of whole chicken by weight — then three quality grains. Purina ONE follows with rice flour, then corn protein meal, whole grain corn, and chicken by-product meal. That's two corn-derived ingredients and a by-product in the top five.
The difference in formula philosophy is stark. Diamond Naturals is built around animal protein and whole grains. Purina ONE is built around one named protein padded with cheap plant proteins and by-products to hit its guaranteed analysis numbers. The ingredient lists read like two completely different price tiers — except they cost roughly the same.
Where Diamond Naturals pulls ahead
Protein quality: Diamond Naturals gets its protein from chicken and chicken meal — two named animal sources. Purina ONE gets protein from chicken, chicken by-product meal, corn protein meal, and soybean meal. When a significant portion of your protein comes from corn and soy rather than meat, the protein percentage on the label doesn't tell the whole story. Animal proteins provide a more complete amino acid profile that dogs utilize more efficiently.
No corn, no soy: Diamond Naturals uses brown rice, barley, and white rice as its carbohydrate sources. No corn derivatives, no soybean meal, no wheat. Purina ONE relies on corn protein meal, whole grain corn, whole grain wheat, and soybean meal — all cheaper ingredients that are more likely to cause sensitivities in some dogs.
Functional extras: Diamond Naturals includes chicory root prebiotics, kale, blueberries, chia seed, coconut, flaxseed, and fish meal. Purina ONE has none of these. No probiotics, no omega-3 supplements, no superfood antioxidants. Diamond Naturals provides a complete nutritional package where Purina ONE provides the bare minimum.
No cosmetic additives: Purina ONE includes caramel color — a purely cosmetic additive that makes the kibble look more appealing to humans but serves zero nutritional purpose for dogs. Diamond Naturals doesn't add any artificial coloring. Shop on Amazon →
Where Purina ONE holds its own
Purina ONE's biggest advantage is availability. You can find it at virtually every grocery store, big-box retailer, and pharmacy in the country. Diamond Naturals has wider distribution than many premium brands but still requires a pet store or feed store in most areas. If convenience is your top priority, Purina ONE is easier to grab on a routine shopping trip.
Purina also has decades of feeding trial data and veterinary research behind its products. While ingredient quality is our focus at KibbleIQ, the fact that Purina conducts AAFCO feeding trials (not just nutrient profile testing) means their formulas have been validated in real dogs over time. That's a legitimate point in their favor.
The price is essentially the same — both typically run $35-45 for a 40-pound bag. Neither brand asks a premium, which makes the quality gap between them all the more notable. Shop on Amazon →
The bottom line
This is one of the most lopsided comparisons at the same price point in our entire database. Diamond Naturals outscores Purina ONE by 20 points — a gap that spans from the low end of C to the upper end of B. For roughly the same cost per bag, you get named animal proteins instead of by-products, whole grains instead of corn and soy, plus probiotics, omega-3s, and superfood antioxidants that Purina ONE doesn't offer at all.
If you're currently feeding Purina ONE and wondering whether it's worth switching, Diamond Naturals is the answer. It's the single most impactful upgrade you can make without increasing your budget. Read our full reviews of Purina ONE and Diamond Naturals for the complete breakdown.