“Fast food makes you sick.”
[That was probably writing by a person who can readily afford tablecloth dining.]
Not all of it. And probably not even the majority of it.
I suspect fried food is rather bad for human health.
I suspect the soda, more than the food, leads to obesity. This is from the carbohydrate sweeteners and also from the carbonation breaking up the food much faster in the stomach.
Not must fast food is cheaper than cooking economically at home.