I think I may have figured it out now. I made a funny observation at my Burger King restaurant: I did not see one obese person, including the personnel. 90% were actually pretty slim, 10% maybe a little overweight, all were enjoying life, eating foods they like. That only leaves one conclusion: In the US, they add a secret ingredient called "junk" to all the delicious foods we like to eat in Europe. This ingredient makes people fat. That's my new theory.