Having just spent a few in Europe I can tell you why Europeans are thinner. Having been overweight most of my adult life I am very aware of how I am looked at. It's not because their diet is any better. What they eat is completely classified as unhealthy here. It's not because they are more fitness conscious. It is because they walk and walk and walk some more, out of necessity, not exercise. The streets are difficult to traverse due to cobblestone surfaces, there are hills and so many huge staircases that allow moving from one level to another either in natural landscape or subways, etc. They just do not sit on there butts and drive cars everywhere there is to go. The price of fuel is a major force in creating that life style and their public transportation system is so good that driving isn't really the best way to do things. However, getting to that transportation requires the flexing of muscle that Americans have not flexed in years. Poverty may contribute to obesity, but, it isn't the cause... it's lack of activity. But hey, it is always fun to look down our noses at fat people, it makes us all feel so much better about ourselves. (Yes, that was sarcasm)
I spent two weeks plus portions of 5 days walking the mean streets in France, Italy and Spain. Those last five days were Ports of Call from a Cruise Ship. I didn't have a way to weigh myself (or desire), but, the last fourteen days were on a transatlantic cruise. Anyone that has ever been on a cruise knows the lure of the sea is mostly unlimited food supply. In spite of that last 14 days, when I arrive home I was 5 lbs. lighter then when I left. ***
*** It is estimated that, on average, cruise passengers will gain 3 lbs. per day, due to inactivity and massive caloric input, so just doing a little math will tell you how much weight must have been lost during the beginning of the trip.