The scores
Purina Pro Plan: C (62/100) — Average. Chicken leads, but by-product meal and soybean meal bring it down.
Hill's Science Diet: C (61/100) — 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
With a single point separating them, there's no meaningful winner here. Both Purina Pro Plan and Hill's Science Diet are solidly average C-grade foods that do the job but don't impress on ingredients. Pro Plan leans on plant proteins and by-products; Hill's leans on grains. Different paths to the same result.
If your dog is thriving on either brand and your vet approves, there's no urgent reason to switch. But if you're shopping fresh and want more for your money, brands like Blue Buffalo, Taste of the Wild, and Diamond Naturals all score B (78/100) — a full grade higher — at comparable or lower prices. Read our full reviews of Purina Pro Plan and Hill's Science Diet for the complete analysis.