I let my daughters tell me if they want to eat or not when they get sick. I am not worried if they don't want to eat for a while. Your body really does sometimes need to concentrate on getting the toxic crap out. Drinking broth should provide you all you need until your hunger returns. If you nibble around and don't want more right now, you are still doing okay. I have done two 10-day fasts before and not wasted away to nothing, so a few days of low-eating because you are sick won't harm you. Your hunger will return soon.
I don't know how many calories my daughters consume because we don't track anything at all. We just make sure the food is safe (as two of my four have allergies and such), of high quality, and that there is enough there to make everybody stuffed if that is how they all are feeling at mealtime. Over a week's time, it all balances out.