Find out what the cat was already eating
When possible, begin with the food the cat has been eating in foster care or at the shelter. A move already changes smells, routines, people, and territory. Changing food at the same time can add digestive upset and make it harder to tell whether reduced appetite comes from stress, preference, or illness.
Transition deliberately
If a diet change is appropriate, mix the new food in gradually rather than replacing the old meal overnight. The pace depends on the cat and the reason for the change. Cats with medical diets or digestive problems may need a specific plan from a veterinarian. Avoid using hunger as a strategy to force acceptance of a new food.
Measure enough to notice change
You do not need a laboratory spreadsheet, but you should know whether the cat ate most, half, or almost none of a meal. For multi-cat homes, separate feeding during the adjustment period can reveal who is actually eating. Note vomiting, diarrhea, constipation, unusual thirst, or a sudden preference change.
Protect quiet eating space
A rescue cat may not eat well if another animal watches the bowl, a washing machine starts nearby, or people repeatedly approach. Place meals where the cat can see the room and leave easily. Some shy cats eat better with a person absent; others begin eating when a trusted person sits quietly nearby.
Do not wait too long on a non-eating cat
Cats can become medically unwell when they stop eating, and the risk is not something to solve with internet tricks. Contact a veterinarian promptly if a cat is not eating, especially if there is vomiting, weakness, pain, breathing changes, or another concerning sign. Appetite tracking is useful because it makes that call earlier and more specific.
This article is educational, not a diagnosis. Sudden appetite loss, breathing difficulty, repeated vomiting, trouble urinating, severe lethargy, pain, collapse, or other urgent changes need professional veterinary advice.