Fat of the land

Having just returned from the south of France, it's striking how few people there are overweight, particularly in comparison with where I live in London where probably two-thirds of the population is obese (and the other third emaciated). This French sveltitude is even more striking when you consider the local diet: lots of courses of meat, cheese, desserts; and lest you Atkinsites say otherwise, loads of carbs: breads, patisseries, rice, pasta and all sorts of potato-based dishes. So where are the fat people?
Most authorities recognise obesity as a symptom of poverty; it's pretty obvious when you see how people live that a French peasant is better off than your typical chav. But does the way people eat affect how much they consume? An all-you-can eat restaurant is as inconceivable to your average rural Frenchman as eating an unbattered chicken thigh not served from a bucket would be to most people where I live.
Though it is certainly on the rise, the fast food culture of huge portions in one rapid course remains the exception in France where people take two hours for lunch that will have a minimum of four courses: starter, meat, vegetables (typically served separately), probably cheese and then fruit or some other dessert. While many may mock the vast plates and apparently tiny portions of nouvelle cuisine, few leave a French dining table feeling unsated. Bigger simply isn't best; it's just bigger.