Thanks for your answers
well I did an experiment, separated a sick kitty alone with a bowl of food and made a small script to send me the food status every hour, at first day she ate 14% of the food bowl.
She was at 60% energy when I first rezzed her, so she had around 5 hours to eat before she sleeps for 8 hours then up and eating for more 8 hours then she slept again.
so she been awake for 13 hours to eat during the first 24 hours and the food reached 86%.
I know they don't eat exactly the same every day because it depends on their sleeping hours, but 14% is around 4 days food? I guess hungry kitties eat the normal rate PLUS 3 days food to compensate the 3 days food they starved.
So if you put a kitty in inventory for 3 days it is pointless because they will eat these 3 days food anyway when they have access to food.
And if you have a sick kitty, be sure to have around 14% of food bowl dedicated to it at its first day of recovery.
These are the conclusions I wanted to reach
and I hope I'm right.
I'm still at second day with my sick kitty, 12 hours passed and the food is at 84% so I guess she is eating at normal rate now because she is not very hungry anymore.
Thank you Saga and Tad for the help