The scores
Iams ProActive Health Healthy Aging Adult 7+: C (64/100) — Average. Named chicken first, but chicken by-product meal in second position and multiple corn-family grains hold the score in C territory.
Hill’s Science Diet Adult 7+ Chicken Meal, Barley & Brown Rice: C (64/100) — Average. Named chicken meal first and a grain stack of barley + brewers rice + whole grain wheat + whole grain corn. The formula is built around veterinarian-recommended senior nutrition principles, but the ingredient deck keeps it in C range.
How the ingredients compare
The top five ingredients:
Iams Healthy Aging: Chicken, Chicken By-Product Meal, Ground Barley, Ground Whole Grain Corn, Ground Whole Grain Sorghum
Hill’s Science Diet Adult 7+: Chicken Meal, Cracked Pearled Barley, Brewers Rice, Whole Grain Wheat, Whole Grain Corn
Both formulas are grain-inclusive and built around a single named animal protein. The structural difference is in how they execute the protein slot. Iams leads with fresh chicken (80% moisture in raw form, shrinks substantially during extrusion) and backs it with chicken by-product meal — which is AAFCO-defined as clean, ground, rendered parts of the carcass excluding feathers, hair, horn, teeth, hooves, and contents of the digestive tract. Nutritionally, by-product meal is dense in bioavailable organ meats and delivers more post-extrusion protein than fresh chicken alone. Hill’s uses chicken meal (rendered skeletal muscle + bone, no organs) in position one, which is the cleaner-sounding choice but not automatically nutritionally superior to by-product meal. Both approaches satisfy AAFCO senior-maintenance requirements.
Further down, Iams adds chicken fat, dried plain beet pulp, egg product, natural flavor, fish oil, flaxseed, a vitamin/mineral premix, and L-carnitine. Hill’s adds chicken fat, soybean meal, egg product, dried beet pulp, flaxseed, chicken liver flavor, lactic acid, and a premix that includes taurine, L-carnitine, and a proprietary antioxidant blend. Both formulas hit the senior-specific talking points — L-carnitine for lean muscle preservation, omega-3 fatty acids from flax and fish oil for joint and cognitive support, moderated fat for aging metabolism.
Where Iams pulls ahead
Price per pound: Iams is materially cheaper than Hill’s Science Diet on most retail channels — often 30–40% less at Walmart, Amazon, and Chewy. For the same-score formula, that’s a real household-budget advantage, especially for owners feeding a larger senior dog or multi-dog households.
Named fresh chicken in position one: Even though chicken-first-fresh isn’t automatically better than chicken-meal-first, it’s the labeling convention most pet owners expect. Iams delivers that expectation at a budget price point.
Sorghum instead of wheat: Iams uses sorghum as its third grain where Hill’s uses wheat. Sorghum is lower on the glycemic index and is generally better tolerated by dogs with wheat sensitivity — a meaningful edge for aging dogs developing new food sensitivities. Shop on Amazon →
Where Hill’s Science Diet holds its own
Veterinary recommendation footprint: Hill’s is the single most commonly recommended brand in US small-animal veterinary clinics. The formula is engineered around published senior-dog nutrition research and the company funds peer-reviewed studies on companion-animal nutrition. That matters for owners who want a brand their vet can speak to confidently.
Named organ meat absent: By not including by-product meal, Hill’s delivers a cleaner-sounding ingredient deck for owners who prefer the clarity of chicken meal without the by-product-meal question. Whether that’s nutritionally superior is debatable; whether it’s easier to explain to a worried owner isn’t.
Added taurine + proprietary antioxidant blend: Hill’s includes taurine supplementation (supports aging cardiac function) and a proprietary antioxidant blend in the premix. Iams Healthy Aging has taurine naturally present from the chicken, but Hill’s calls out the supplemented level explicitly — a meaningful signal for at-risk breeds (Cocker Spaniels, Golden Retrievers, Newfoundlands). Shop on Amazon →
The bottom line
If your senior dog is doing well on a middle-tier kibble and you’re cost-conscious, Iams Healthy Aging is the right pick — same score, same broad nutrition profile, materially lower price. If your vet has specifically recommended Hill’s or your senior dog has complex health management needs, Hill’s Science Diet Adult 7+ is worth the markup for the clinical-research backing alone. Neither is a standout ingredient story — both are C-grade grain-inclusive formulas — but both are acceptable baseline senior nutrition. Owners looking for a clear step up in ingredient quality should read our guides to best dog food for senior dogs.