Why is my cat losing weight after switching to adult cat food?

I wouldn't think that a decrease in appetite and weight loss would result from a diet change. Some cats can be quite picky and will stop eating a food they previously liked or be hesitant to try a new food, but eventually these cats will eat once they get hungry enough and picky eating should not result in significant weight loss. I wouldn't be concerned about changing to an adult food in an 11 month old cat either - Kovu was probably very close to his adult height by that point. I think seeing your veterinarian to have Kovu's weight checked and for a complete physical exam sounds like a great idea, and if they feel he is in good health you can discuss trying to find good quality diet that he seems to like and then monitor his weight closely.

This kind of dramatic weight loss is almost always due to an underlying medical condition. Ask your vet if he has checked Frida Katio's thyroid levels to rule out hyperthyroidism and performed full body X-rays to scan for any masses. He should also perform full mouth dental X-rays to rule out any dental disease that may be preventing her from eating. If all of these diseases have been ruled out, you could consider switching Frida to a higher calorie canned food such as Hills Science Diet AD.

Weight loss coupled with a normal or increased appetite can be a sign of diabetes or hyperthyroidism, to name a couple of possibilities. I recommend getting Felix seen by your vet as soon as possible for an exam and labwork to determine the reason for his weight loss and get him started on treatment.

2-6 Kg is the amount he needs, if you use the dosage above this one you are risking toxicity. it is not normal at all to lose more than half of his weight, i would say it is very likely that he is suffering from a disease in the background that is causing this, i strongly recommend taking him to the vet ASAP in order to get it checked.

Weight loss is possible due to increased activity, but 9kg to 4kg is more drastic than I would expect. I would discuss doing bloodwork with your vet. Increased activity and weight loss is common in cats with hyperthyroidism. Weight loss can also be caused by kidney disease and diabetes. All 3 of these conditions can be diagnosed with simple bloodwork (CBC, chemistry, thyroid panel) and urinalysis.

Based on the photos, Ella appears to be a healthy weight - however, any unexplained weight loss is always worth investigating. Your friend is correct that worms can cause weight loss. Other possibilities include decreased appetite, vomiting, increased activity, or possibly something more serious. It would be ideal to establish care with a veterinarian so that you can start a log of her weight over time, to determine how much she is losing. Your veterinarian can check a fecal sample for parasites and perform any additional tests as needed.

I would recommend taking Oliver Paul into for an exam by a veterinarian. They can do a full exam, and a geriatric blood work panel. They may also take his blood pressure. High blood pressure can cause weight loss in older kitties. It can also cause eye problems. Another common and treatable condition in older kitties is hyperthyroidism. They get benign (non-cancerous) tumors on their thyroid gland that causes them to produce too much hormone which up regulates their metabolism. They will eat a lot and continue to drop weight. A veterinarian can get Oliver on a plan to recovery! Thanks for reaching out to Petco Pet Education Center, formerly Petcoach!