The scores
Purina Pro Plan: C (58/100) — Average. Chicken leads, but by-product meal and soybean meal bring it down.
Hill's Science Diet: B (75/100) — Average. Chicken leads, but four grains fill positions 2 through 5.
How the ingredients compare
The top five ingredients reveal two different strategies for landing in the same mediocre spot:
Purina Pro Plan: Chicken, Rice, Poultry By-Product Meal, Soybean Meal, Corn Protein Meal
Hill's Science Diet: Chicken, Cracked Pearled Barley, Brown Rice, Brewers Rice, Whole Grain Wheat
Pro Plan uses one animal protein, one grain, and then leans on by-product meal and plant proteins. Hill's uses one animal protein and then four consecutive grains. Both end up in the same place — a lot of the food is carbohydrates and plant-based fillers rather than animal protein.
Where Purina Pro Plan has a slight edge
Protein diversity: Pro Plan at least includes poultry by-product meal as a secondary animal protein source, even though it's a lower-quality one. Hill's has chicken alone as its animal protein in the top five, followed by nothing but grains. By-product meal isn't ideal, but it does contribute real animal protein.
Formula variety: Pro Plan has one of the largest product lines in the industry. Sensitive skin, sport formulas, age-specific options, breed-size formulas — whatever your dog needs, there's probably a Pro Plan variant. Hill's has variety too, but Pro Plan's lineup is broader. Shop on Amazon →
Where Hill's Science Diet holds its own
Better grain selection: Cracked pearled barley, brown rice, and whole grain wheat are more nutritious grain choices than Pro Plan's rice and corn protein meal. Barley in particular is a solid whole grain with good fiber content. Hill's isn't hiding plant proteins behind ingredient names the way Pro Plan does with soybean meal and corn protein meal.
No by-products: Hill's avoids poultry by-product meal entirely. Whether that matters nutritionally is debatable — by-product meal is still protein — but many pet owners prefer to avoid it, and Hill's delivers on that preference.
Veterinary ecosystem: Hill's has the deepest veterinary relationship of any pet food brand. Their prescription diet line is the go-to for therapeutic nutrition, and their regular formulas benefit from that research pipeline. If your vet has a specific recommendation for Hill's, there's likely solid science behind it. Shop on Amazon →
The bottom line
Hill's Science Diet wins by 17 points (B/75 vs C/58), a full grade tier. Both brands rely on plant-heavy ingredient profiles, but Hill's quality-whole-grain approach (cracked pearled barley, brown rice, brewers rice, whole grain wheat) outperforms Pro Plan's by-product-meal-plus-plant-protein strategy on the KibbleIQ rubric. Both deliver acceptable nutrition with strong feeding-trial substantiation per AAFCO Dog Food Nutrient Profiles, but Pro Plan trails meaningfully on ingredient transparency.
If your dog is thriving on either brand and your vet approves, there's no urgent reason to switch. If you're shopping fresh, several B-grade mainstream alternatives outscore both. Blue Buffalo (B/78), Taste of the Wild (B/78), and Diamond Naturals (B/78) all score 3 points above Hill's Science Diet and 20 points above Purina Pro Plan at comparable or lower prices. Read our full reviews of Purina Pro Plan and Hill's Science Diet for the complete analysis.