A client once asked me, completely sincerely, whether she could feed her adult Labrador and her adult cat the same food to simplify her shopping. She'd been doing it for three years. The cat was fine in some respects, the Lab was also fine — but the cat had been slowly developing taurine deficiency-related issues that we only caught on a routine exam. The cat's retinas were showing early signs of degeneration.
Dog food doesn't contain taurine. Cats need it. These are not interchangeable diets.
I tell this story not to alarm anyone — we caught it, changed the diet, and the cat recovered — but because it illustrates something important about feeding adult pets: dogs and cats have genuinely different nutritional needs, and understanding those differences is the foundation of feeding either one well.
Dogs: Omnivores with Flexible Needs
Dogs evolved alongside humans eating a varied diet, and their digestive systems reflect that. They can synthesize many nutrients their bodies need, have a functional pancreatic enzyme system for starch digestion, and are generally adaptable in what macronutrient ratios they thrive on.
That said, adult dogs do need adequate protein — more than the old guidance suggested. The minimum AAFCO standard for adult dog maintenance is 18% protein on a dry matter basis, but many veterinary nutritionists now recommend higher amounts, particularly for active dogs and those maintaining muscle mass as they age — a position supported by research showing that older dogs actually need protein levels higher than the minimum to prevent sarcopenia, rather than less. Fat is the primary energy source for dogs and also provides essential fatty acids (specifically omega-6 and omega-3 precursors) that dogs can't synthesize. Carbohydrates aren't strictly required, but they're a perfectly valid energy source that most dogs handle well.
What does this look like in practice? For most adult dogs at maintenance, a complete and balanced commercial food with protein as the first ingredient, moderate fat (around 10–15% on a dry matter basis for inactive dogs, higher for active ones), and adequate fiber is the baseline. The specific macronutrient numbers matter less than whether the dog's body condition score stays in the appropriate range.
Cats: Obligate Carnivores, Non-Negotiably
Cats are a different physiological story entirely.
Cats cannot synthesize taurine, arachidonic acid, or niacin in adequate quantities — these must come from dietary animal tissue. They have very limited ability to regulate protein breakdown (meaning they continue breaking down protein for energy even when dietary protein is low, unlike dogs). They have a low thirst drive and evolved to meet most of their water needs through prey tissue, which is why dry food-only diets often produce chronic mild dehydration in cats, contributing to urinary problems over time. And their livers process certain things differently — including the fact that they cannot safely metabolize certain fats and synthetic additives that dogs handle easily.
The practical implications are significant. Adult cats need protein levels that most dog foods don't provide. They need fat that includes arachidonic acid from animal sources. They benefit substantially from dietary moisture — wet food, raw food, or at minimum consistent water intake alongside dry. And they cannot thrive on vegetarian or vegan diets. Full stop.
Taurine deficiency is one of the most preventable serious conditions in cats, and it happens when owners feed dog food, homemade diets without supplementation, or very low-quality cat foods that don't meet AAFCO standards for cats. The consequences — dilated cardiomyopathy and feline central retinal degeneration — were established definitively in research from the 1970s through late 1980s, leading to widespread cat food reformulation. Unlike dogs, cats cannot synthesize adequate taurine endogenously; it must come from dietary animal tissue. If your cat's food doesn't say "complete and balanced for adult cats" or cite an AAFCO or equivalent nutrient profile for cats, it's not meeting these requirements.
Life Stage: Why "Adult" Matters
Both dogs and cats need different nutrient profiles at different life stages: growth (puppy/kitten), adult maintenance, and senior. The transition from puppy or kitten food to adult food is typically recommended at:
- Small and medium breeds: 9–12 months
- Large breeds: 12–15 months
- Giant breeds: 15–18 months
- Cats: typically 12 months, though some nutritionists suggest extending kitten feeding if the cat is still lean
Why does this matter? Growth foods are formulated with higher protein, more calcium, and more calories per gram to support rapid development. Continuing to feed a growth formula to an adult dog or cat who's done growing can contribute to weight gain and, in dogs, potentially to excessive mineral intake over time.
The reverse is also true: feeding an adult maintenance food to a growing puppy or kitten can leave them short on the building blocks they need. The lifecycle designation on the bag isn't marketing — it reflects genuinely different formulation targets.
Protein Quality: Not Just How Much, But What Kind
Protein quantity on a pet food label tells you less than you'd think. What matters is protein digestibility and amino acid completeness — neither of which appears on the guaranteed analysis.
High-quality animal proteins (chicken, turkey, fish, beef, egg) have excellent amino acid profiles and digestibility rates. Some plant proteins (corn gluten meal, soy protein isolate) have decent amino acid profiles but lower digestibility. Meat byproduct meals vary widely — some are excellent nutritional sources, some are not — and the label doesn't tell you which.
In practice, the best indicator of protein quality isn't parsing the label — it's the AAFCO feeding trial statement or nutrient profile certification. A food that passed an AAFCO feeding trial for adult maintenance has been verified to maintain animals on that diet, not just to contain the right numbers on paper. That's the more meaningful quality signal.
Body Condition Scoring: The Real Metric
All the guidelines about what to feed and how much ultimately serve one practical test: is your pet at a healthy body condition score?
Body condition scoring (BCS) uses a 9-point scale where 1 is severely emaciated and 9 is severely obese. The target for most adult dogs and cats is 4–5: ribs easily felt without excess fat cover, visible waist from above, a slight abdominal tuck when viewed from the side. Cats at ideal BCS typically have a slight fat pad over the belly but not a pronounced pouch.
BCS is something you assess with your hands as much as your eyes. Run your hands along the ribcage. If you can feel the ribs without pressing hard, that's normal. If you have to push through fat to locate them, the animal is overweight. If they're visible without any pressure, the animal is underweight.
I show clients how to do this at every annual exam. It takes fifteen seconds, requires no equipment, and gives you an ongoing monitoring tool that's more responsive than a quarterly weigh-in.
How Much to Actually Feed
The single most useful thing I can tell you about feeding amounts: the bag guidelines are a starting point, not a prescription.
Pet food companies calculate feeding guidelines based on average dogs or cats of a given weight. Your dog or cat is not average. Body condition, activity level, whether they're spayed or neutered (neutering reduces caloric needs by approximately 20–30% — a figure consistent with research published in Nutrition Research Reviews (2020), which documented reduced basal metabolic rate following gonadectomy in both dogs and cats), metabolic rate, and health status all affect how much food is appropriate. The guidelines tend to run generous, because it's better commercially to have pet owners feeding more.
Start with the lower end of the range for your pet's weight. Weigh your pet monthly. Adjust portions by 10–15% up or down based on body condition trends. That's the actual protocol.
For more detail on how activity level and size change the equation for dogs, see adjusting your adult dog's diet for activity level and size. For cats specifically, what and how much to feed an adult cat covers the unique factors that make feline feeding calibration its own topic.
When the Current Diet Isn't Working
Signs that a current diet needs adjustment include:
- Consistent weight gain or loss despite appropriate portions
- Coat quality that's deteriorating: dry, dull, excessive shedding
- Chronic soft stool, frequent gas, or intermittent vomiting
- Low energy or poor muscle condition in a dog or cat who should be thriving
- Skin issues that don't resolve with other treatment
These signs don't always point to diet — plenty of health conditions produce them too. But if bloodwork and a physical exam have ruled out underlying disease, food is a reasonable next place to look. Working with a veterinary nutritionist for a reformulation recommendation is worth doing rather than experimenting on your own, particularly for cats.
A Few Things I Wish Pet Owners Knew
Grain-free doesn't mean healthier. The FDA investigated a potential link between grain-free diets and dilated cardiomyopathy in dogs between 2018 and 2019, publishing an alert identifying certain grain-free legume-heavy diets in association with DCM reports. The investigation did not establish a definitive causal mechanism, and the FDA has not mandated recalls, but the episode underscored that trendy is not the same as evidence-based.
Raw feeding is not automatically superior. Done correctly with appropriate supplementation, raw diets can support health. Done incorrectly — which is common — they lead to nutritional deficiencies and food safety risks. The appeal is understandable; the risks are real.
Cats eating only dry food are in a chronic state of mild dehydration in many cases. This isn't dramatic — cats evolved to be efficient — but it does contribute to urinary tract issues over time. If your cat refuses wet food, water fountains, ice cubes, and flavor additions to water bowls are worth trying.
And finally: if your pet is doing well on a diet — good body condition, great energy, excellent coat, normal digestion — don't fix it. The best diet is the one your individual animal thrives on, not the one currently trending in pet nutrition circles.