[Answerawake]

I agree with you. I also feel ill after eating KFC. It seems more greasy than something like Popeyes. My body feels like it has had a sucker punch after eating KFC so I try to stay clear. My theory is that it is a combination of something in the breading they use + the method of frying.

KFC uses a Pressure Fryer: https://youtu.be/9ZLKj2a_OPM?t=546

Wendys and Chickfila also use a pressure fryer but notably their sandwiches are not dripping with oil when you order them.

Here is the same pressure fryer Wendys uses but to fry chicken wings instead of sandwich patties, noice that they are dripping with oil: https://youtu.be/7owZz26W1_U?t=176

Popeyes uses a standard fryer plus a thick coating of buttermilk(as seen earlier in the video) and their chicken seems to come out cleaner: https://youtu.be/31dGYRnhS8k?t=113

Seems like Pressure fryers + breading might be the culprit but really, this is just a wild guess. If there are any fried chicken masters here, feel free to jump in.