A food trial fails as evidence long before it fails as a diet, usually because three things changed in the same fortnight and nobody wrote down the order. Your vet needs a clean sequence: what the cat ate before, exactly what changed, on which day, and what the body did next. A simple daily log, kept with discipline, provides that sequence.
The Fields, Kept Identical Every Day
Use the same nine fields for every entry: day; food served, copied exactly from the packaging; amount offered, weighed in grams; amount eaten, also weighed; appetite, noted as keen, picky or unchanged; stool, described as formed, soft or absent; vomiting, recorded as none or timed; skin and coat; and energy, noted as normal, flat or restless. Identical fields matter because gaps are invisible in free-form notes; an empty stool column on the day you were busy is obvious in a structured log, and the vet can scan a month in minutes.
Record amounts in grams weighed, not handfuls or scoops described loosely, and name the food served precisely: flavour, protein source and form, wet or dry, copied from the packaging you photographed at the start. If the recipe changes mid-trial because a flavour was unavailable, that is a new entry and a break in the trial, and the log should say so rather than smoothing it over.
A Worked Example With Real Values
One honest day might read: Day 8; food served, new single-protein wet food, turkey recipe; amount offered, 85 grams at breakfast and 85 grams at dinner; amount eaten, 70 grams in the morning and all 85 grams in the evening; appetite, keen, finished dinner quickly; stool, one formed stool, no diarrhoea; vomiting, none; skin and coat, scratched ears twice in the evening, coat unchanged; energy, normal, played for ten minutes after dinner.
That entry took under a minute and it answers the vet's real questions: exposure was almost complete, intake was good, one symptom appeared once, and nothing else changed that day. Thirty entries like it show a trend no memory can reconstruct.
Trial Discipline the Vet Will Ask About
Change one thing at a time. Introducing a new food, a new treat and a new supplement in the same week makes every later symptom unassignable, and the trial has to restart. Stage the changeover over several days as your vet directs, mixing increasing proportions of new food with the old, and log the proportions during that week because symptoms during transition mean something different from symptoms on the full new diet.
Hold the trial for the full length agreed with your vet, which is often several weeks for skin or digestive questions, and resist judging it at day five. Log treats, dental chews, flavoured medicines, table scraps and food stolen from another pet's bowl, because all of them are exposure, and a trial described as strict that quietly included daily treats misleads everyone.
What the Log Can and Cannot Tell the Vet
Bring the log, the packaging photographs and a note of the exact day each change happened to the appointment, and let the vet interpret the pattern. Improvement during a trial can have several explanations, and symptoms can persist for reasons the log alone cannot separate; the article you are reading cannot diagnose an allergy or an intolerance from your entries, and neither can the log by itself.
What it can do is remove guessing. Instead of reporting that the cat seemed a bit better sometime last month, you can show intake, symptoms and timing day by day, which lets the vet decide whether to extend the trial, test a further change, or investigate something unrelated to food.
Stored with the rest of the health history in KinsLe, the trial log sits inside your cat's Pet Passport ready for the next appointment or a locum vet.