Junk food - something we all know is not good for our health but still can't resist its delicious taste and fascinating texture just because of the science that is put into the process of making it. The amount of sugar, salt, timing, oil, fatness,... is calculated thoroughly to achieve a PERFECT PROPORTION. It is designed to make us addicted to it and crave more after each bite we take and disables us from stopping.
However, what we usually get is empty calories with a huge amount of fat and sodium. It affects our health drastically to the point that you immediately feel horrible after consuming a large amount of it. But then you will come back for more after the terrible feeling is gone.
After all, it's all up to you to decide if it's worth it to eat junk food. A bag of chips once in a while is not too much of a problem, but more often than that, you'd better watch out.