My kitten in 3 month old and losing weight due to diarrhea. Before de-worming, diarrhea was with blood, but now it is just stool. We give boiled chicken and kitten food (ROYAL CANIN). And sometimes yogurt and boiled rice. I asked the Vet but he says change the cat food. It is the same cat food that he suggested me during de-worming. So I bought 2kg bag. I am confused now what to feed to my kitten. Is it boiled chicken? Or the kitten food causing diarrhea.
Ask your vet to clarify what they meant by changing the cat food.
My recommendation would be to feed only the Royal Canin kitten food. The yoghurt or boiled rice could be causing digestive issues, and are not part of an appropriate diet for a kitten or cat. Small amounts of chicken are likely not be a problem as long as the chicken is not flavoured and fully cooked, however until the diarrhea has resolved I would feed only the kitten food.
There are hundreds of different causes of diarrhea in kittens, ranging from the simple-to-treat (parasites) to difficult-to-treat (allergies), with every bacterium and virus in between. Some kittens will respond well to simplifying the diet, while others need further workup (bloodwork, fecal, possibly x-rays, etc) to get to an answer and appropriate treatment. Some kittens will become very dehydrated with severe diarrhea so it is important to not let diarrhea go untreated for too long.
Only have two things to add to the other answer:
Watch the cat throughout the day, make sure they're not eating something they shouldn't be (like plants or carpet fibers). If you can't do that, maybe put them in a clean room where they can't get anything bad.
Also, please take your cat to get a workup at the vet! Would you like to have horrible chronic diarrhea? It probably won't be that expensive. Think of it as an investment that will pay out over 10-20 years of your cat's friendship.