As a first generation German who spent time living in Germany as a child I think I can put some of this in perspective.
1. There is intense pressure in Germany to conform and follow the rules. Being fat is a major sin and will bring about all sorts of abuse and very overt condemnation, much worse than what is found in the states. Usually in the U.S. the merciless teasing abates after High School, in Germany it never ever ends. The only acceptable obese person in Germany is an elderly man, kinda like Schultz from Hogan's Hero's. I think Levi, that many of the very obese "Do the right thing" and stay out of the public eye, or commit suicide.
2. Europe has free medical care. In the U.S. many of the very obese are low-income and therefore have no health insurance therefore they get no care, none, nada, zilch.
3. Most German schools are much more physical education minded. Many American schools have completly removed these programs from the curriculem. (To save money). Yes it's true, it's all about the dollar in America.
4. If I remember correctly the Germans have one big meal a day at lunchtime, this was the hot cooked meal of the day were all the carbs are. Plenty of time to burn em off. Dinner is usually cold cuts and high grain breads. There's no Wonderbread in Germany!
5. Childrens TV in europe is much more responsible. No commercials till the end of the show and the pushing of carb-filled suger treats much less intense. (All about the money)
6. I was hard pressed to find Potato or Corn Chips until the 80's in Germany. God I hated that, though the peanut butter cheese puffs were pretty damm good.
7. Much less processed foods in Europe. I think Europe is catching up though.
Here's me in 1972 in my lederhosen. My parents thought I had a weight problem! I do now.