I have moved to Switzerland where the women here actually have the lowest BMI in Europe - suprisingly not the French, but of course Swiss aren't considered "Europeans". Interestingly you see more of a median here - everyone is around the average.
What do they do differently:
They still eat fatty foods - chocolate, butter, croissants etc, but they eat less generally - food is expensive, meat is very expensive, portion sizes are much smaller. Although we claim the UK is a rip off, food is actually very cheap compared to a lot of other countries.
Birchermuesli is a popular and common breakfast dish.
They generally have a two hour lunch break here and eat their main meal at this time of the day, and a smaller evening meal.
Food is generally simple, seasonal and rarely convenience.
Majority of Swiss mums are stay at home or part time so they have time to cook from scratch.
Everyone walks, all the time, for the majority of people this is the form of exercise. Every evening, weekend you see families all out walking - round the towns, villages, forests etc for at least an hour a day.
Private healthcare - if you have to pay extra for your healthcare because you're fat (and this happened to me when I moved here
, it can cost you an extra £120 a month as a couple! Also you'll get charged extra if you have to have an op/treatment linked to your obesity. When you rely on the NHS to pick up the bill it doesn't cost you to pay for your diabetes tablets, heart tablets, high blood pressure meds etc.
If it costs you money to be fat, you'll try your best to be thin. Believe me!