Thought I would update this thread since I have just returned from another 2 weeks in Italy. I was thinking about this thread - believe it or not - as we drove a few thousand kms. around rural Italy plus spent 2 days in Rome. What struck me upon landing in Rome and especially upon returning to Toronto was the enormous difference in weight between the typical Italian and the typical North American. Almost all Italians we saw are slender. Yes, there are a few moderately hefty ones, but that was rare. What struck me even more was that Italians wear very tight fitting pants. Italians have always been very fashion conscious and skin tight pants (especially leather) on women greatly distracted me from viewing the sights of Rome.

You can easily pick out the American tourists by their size and their clothing.
Most North Americans misunderstand the Mediterranean diet. It's not just better quality, less processed food, but also far less of all food. The portion sizes are significantly smaller, with the emphasis on fresh, natural tastes and far less use of salt & spices than we are accustomed to. You almost never see french fries or hamburgers on a menu and McDonalds puts the emphasis on McCafe not burgers. Meat portions in particular are half or less than we see in American restaurants.
The average Italian walks a lot more than we do. Even in large cities, walking briskly to/from cars or transit is normal. At home, I pass almost everyone when walking. In Italy, I had to step up my pace to be average. Actually, they do everything faster especially driving. It's the same phenomena we notice when going the the Caribbean, where everything slows down significantly. In Italy, the pace speeds up compared to our normal. It's also not just walking but a ton of steps and steep inclines. Rome was built on hills, Venice is full of bridges, rural towns are almost always on the tops of mountains and everywhere you go, you're climbing.
So IMHO, it's all about smaller portions, natural ingredients and a lot more exercise if you want a longer, more healthy life.