Saturated fats, trans fats and in fact all fats are bad for you. imitation sugars can cause cancer in lab rats and ice cream can give you a headache. Allergic reactions can happen with any drug and can range from itching and rash all the way up to a life-threatening anaphylactic reaction. You could step off a curb practicing for your 10k run tomorrow and get hit by a bus..
Of course worrying about all these things are bad for you health too, so just enjoy life!!!