Regular consumption of junk food is one of the leading factors responsible for obesity. Junk foods don't provide you with any essential nutrient, even though they can be very much sufficing, you feel weakened.
Fast food is grossly filled with refined foods, sugars and salts. If you have high blood pressure or cholesterol, it is probably one of the worst things you can have.
Fried foods taste good, but they are terrible for you, especially foods fried in partially hydrogenated or trans fat oils. These oils lower good cholesterol and increase bad cholesterol.