We've been in Paris for over a week now and everywhere we go it (happily) surprises me to see so few obese folks. Forget about obese, there is rarely a fat Parisian to be found!
Unfortunately I can't say that I'm happily amazed at their healthiness because the majority smokes like a chimney but other than that they look very good.
Being here and enjoying delicious, DELICIOUS food, I've noticed how intense flavors and smells are. A strawberry doesn't taste like a normal strawberry, it's like strawberry infused with strawberry juice.
Besides the fact that people walk every day around the city, I think that this richness in the food is the key to their slim figures. When you eat something that tastes so intense you can't eat as much! ;-)
What if we all have a flavor quota? What if you can only tolerate a fixed amount of a flavor per meal or per day? You enjoy the food immensely but you eat less! And you're walking around everywhere, burning calories!
Voila! The formula to a life full of delicious French cheese, wine, foie gras, macarons, croissants, croque monsieur, baguettes... You name it!