The scores
Diamond Naturals Adult Dog Chicken & Rice: B (78/100) — Good. Chicken plus chicken meal opens, then a brown-rice-and-barley whole-grain base, chicken fat preserved with mixed tocopherols, fish meal for marine protein, salmon oil for DHA, and an extensive vitamin-mineral premix. Independent-pet-store value standard.
WholeHearted Grain-Free All Life Stages Chicken & Pea Recipe: B (77/100) — Good. Chicken plus chicken meal opens, then a three-form pea stack (peas, pea starch, pea protein), tapioca starch, and supplemental taurine. Petco-exclusive grain-free private label.
How the ingredients compare
The top five ingredients:
Diamond Naturals: Chicken, Chicken Meal, Whole Grain Brown Rice, Cracked Pearled Barley, White Rice
WholeHearted: Chicken, Chicken Meal, Peas, Pea Starch, Pea Protein
The two formulas open identically — whole chicken first, then chicken meal — and diverge at position three. Diamond Naturals goes whole-grain (brown rice, pearled barley, white rice), giving the formula a fiber-rich, B-vitamin-dense carbohydrate foundation. WholeHearted goes grain-free with a three-form pea stack (whole peas + pea starch + pea protein), which delivers carbohydrate volume but stacks pea-derived protein concentrates that the rubric flags as a protein-density inflator.
Past position five, Diamond Naturals continues building density: dried yeast (B vitamins), chicken fat preserved with mixed tocopherols, egg product (complete amino acids), dried beet pulp (fermentable fiber), natural flavor, fish meal (marine protein + omega-3 base), flaxseed (plant omega-3), salmon oil (the key DHA/EPA delivery), and supplemental taurine. The fish-meal-plus-salmon-oil combination is meaningful — that’s real EPA and DHA arriving through marine sources, not just plant-derived ALA. WholeHearted’s deeper list is shorter and tighter: chicken fat, tapioca starch, natural flavor, dried beet pulp, flaxseed, and supplemental taurine — no fish oil entry, no salmon oil, no marine-protein source.
The FDA DCM investigation context applies here. Grain-free formulas with high pea-fraction loads remain under scrutiny in genetically predisposed breeds — Diamond Naturals’ grain-inclusive whole-grain architecture is the safer default. WholeHearted is a legitimate grain-free option for dogs with documented grain sensitivity, but for the average dog without a diagnosed sensitivity, the grain-inclusive formula is the recommended pick.
Where Diamond Naturals pulls ahead
Whole-grain carbohydrate foundation. Brown rice, pearled barley, and white rice deliver intact whole-grain fiber, slow-release energy, and naturally-occurring B vitamins. The rubric rewards whole grains over fractionated pea concentrates, and the FDA DCM investigation context favors grain-inclusive formulas for predisposed breeds (Goldens, Dobermans, Boxers, Cocker Spaniels) without requiring a sensitivity workup first.
Direct marine omega-3 sources. Diamond Naturals carries both fish meal and salmon oil — meaningful EPA and DHA arriving through marine sources. Dogs convert plant-derived ALA (from flaxseed) to EPA/DHA inefficiently. The marine sources matter for skin, coat, joint, and brain health, and WholeHearted’s flaxseed-only omega-3 profile does not match this delivery.
Independent pet store distribution. Diamond Naturals is widely available through independent pet stores, online retailers, and feed supply stores nationwide — not locked to a single retail channel. For owners who don’t shop at Petco or who want flexibility on where they restock, the broader distribution is operational value. Shop on Amazon →
Where WholeHearted holds its own
Grain-free for grain-sensitive dogs. Dogs with diagnosed grain sensitivity or specific intolerance to wheat, corn, or rice need the grain-free option, and WholeHearted delivers it at value-tier pricing. Tapioca starch and pea-based carbohydrates fuel the formula without grain. For the small population with documented adverse food reactions to whole grains, this is the right pick.
All Life Stages formulation. WholeHearted meets AAFCO All Life Stages nutritional adequacy — one bag spans puppy through adult through senior. For multi-dog households or owners who want operational simplicity, that single-formula approach is meaningful.
Petco-aisle convenience. For owners already at Petco for other supplies (treats, toys, grooming), WholeHearted is a one-stop pickup. Diamond Naturals isn’t carried at Petco — it requires a separate trip to an independent pet store or a separate online order. Single-store convenience has real value when you’re already there. Shop on Amazon →
The bottom line
If your dog tolerates grains and you have access to an independent pet store or online ordering, Diamond Naturals Adult Chicken & Rice is the one-point winner — B/78 with whole grains, marine omega-3s, and broader distribution. If you’re shopping at Petco specifically and want a grain-free pick at value-tier pricing, WholeHearted Grain-Free Chicken & Pea at B/77 is a legitimate alternative on a single shelf. The choice often comes down to where you shop and whether you need grain-free — both clear the C-tier line. For more value-tier picks, see our best affordable dog food guide.