Like the French, Italians also drink loads of Wine. There's some theory that this has an impact. They also walk a lot more than Americans.

Looking at the UK and Ireland, my few times in those countries (especially Ireland) showed me that fast food and a lack of veggies is pretty common, especially out in the local villages. There were a few entire days while traveling throughout Ireland (as a visitor) where my choices for food in some local village were basically the local fish & chips/pizza place or the pub and that was it. The local children were pretty hefty, but the farmers and other locals were about as fit as that kind of life can make you. I did manage to find a few great local restaurants, but the meals were basically local pork in cream sauces and potatoes with a few greens. It was great food if you're working a farm or something similarly labor intensive, but sedentary lifestyles are not compatible with it.