advice for an extremely fat cat !

Cats are snackers. I would change his food. Alot of the cheaper brands have alot of filler and it is just like eating junk food is for us humans. They have different types of food. Check it out next time you are in the store. Your cat needs some activity too. I would find some activities. Make him some play toys.

I've always free fed, but I've found that getting a premium "lite" food does help them lose weight.

The best way to help your cat lose weight is to switch to canned food. A cat should eat 3 oz of canned food 2X a day. That's half a can. Get a high quality food that has meat as a main ingredient and little or no grain. Switch gradually. I have 4 cats and they all eat twice a day. When they were a bit tubby, I got French cut green beans and mashed them into their canned food. About a tablespoon of beans with the food amount reduced by that much. My cats didn't mind the beans at all and it filled them up without the calories. You should get a lazer pointer so that your cat can chase it around and you don't have to move. Be careful that you don't shine it into the cat's eyes. If you don't mind exercise yourself, drag a shoe lace or a belt around the house behind you. You cat will probably chase it and get some exercise. Good luck. I hope in the meanwhile you wipe him with a cat wipe so he doesn't get matted. My daughter has to bathe her cat's butt as he can't clean himself.

my cat wighing 5,2 kg, held his stomach if he was angry. he may be embarrassed with a fat stomach, my cat be too fat because the work just to eat and sleep

Oh dear. I think the problem is that some cats can be trusted to self-feed, and some can't. First, see if your vet can maybe recommend something that is good for controlling a cat's weight, and have that food available all the time. Try and get your cat interested in something other than food - playing perhaps, which might even be good exercise. If you give him snacks, try to impose some limits (I know, I know, you end up feeling like a total meanie). See if something like a catmint toy can get your cat interested in something other than food. About the grooming, maybe the reason he swipes at you is because it hurts him when you try to get rid of the clumps. All of our cats love being groomed, so I think if you persist, get rid of the clumps and keep doing it, your cat might grow used to it and even grow to love it.