Suitability is a slow verdict, not a single meal
An upset stomach after a stolen kebab or a too-fast dinner says little about a dog's regular food. A food that genuinely does not suit him declares itself slowly, across weeks of ordinary feeding, in systems far from the bowl. Because the signs creep in, owners often adapt around them, scratching cream here, ear cleaner there, without stepping back to ask whether the one constant in his life, the food he eats twice a day, sits underneath the pattern.
The way to answer that question is observation with dates. Single episodes are noise; a sign that recurs, persists or slowly worsens while the food stays the same is a signal worth taking to your vet with a timeline in hand.
Skin, coat and ears tell the earliest story
Persistent itching is the classic non-stomach clue. A dog who licks his paws in the evenings, rubs his face along the carpet or chews at the base of his tail may be reacting to something he eats, although parasites and pollen sit on the same suspect list.
The coat reports alongside the skin. A suitable food usually supports a coat with shine and a skin without constant flaking; a coat that turns dull, brittle or greasy, with dandruff that returns days after a bath, suggests the diet's fats or overall balance are not serving him. Ears complete the trio: repeated head shaking, brown waxy build-up and ear infections that clear then return are frequently seen in dogs whose food is part of the problem, and vets often explore diet when ears relapse for the third time.
Digestion beyond the obvious upset
Suitability also hides in the almost-normal. Stools that are never reliably firm, swinging between acceptable and soft without any dietary indiscretion, point to a gut that tolerates rather than thrives on its food. Relentless wind that clears a room most evenings, frequent grass eating followed by small vomits, borborygmi loud enough to hear across the sofa, and poos of surprising volume for the amount fed, suggesting much is passing through undigested, all belong on the list.
Appetite itself is evidence. A dog who once arrived at the bowl keenly and now sniffs, wanders off and returns reluctantly may be bored, unwell or quietly associating meals with feeling off afterwards. Reluctance plus any of the signs above deserves more respect than reluctance alone.
Weight and energy drift
A food can fail a dog by calibration as much as by ingredient. Steady weight gain on honestly measured portions suggests the food is more energy-dense than his life requires, while a dog who thins despite generous bowls may not be extracting what he needs or may need a vet's wider look rather than a bigger scoop. Energy follows the same logic: a dog who sleeps excessively, tires oddly on familiar walks or loses his sparkle across a season, while eating a food mismatched to his age or activity, is showing you a whole-body review is due.
None of these signs belongs to food alone. Thyroid trouble, pain, allergies to the environment and simple ageing imitate dietary failure convincingly, which is precisely why the response is a veterinary conversation, not an impulsive tour of every protein on the shelf.
What to do with a pattern once you see it
Take the timeline first: when each sign began, how often it occurs, what has already been tried. Change one thing at a time under your vet's guidance, because swapping food, treats, chews and shampoo in the same fortnight destroys the very evidence you need. If a food change is advised, transition gradually and allow a proper settling period before judging it, since skin and ears improve on a slower clock than stomachs.
Recording those dated observations, foods tried and vet findings together in KinsLe Pet Passport turns a vague feeling that his food never quite suited him into a clear history your vet can act on at the first visit.