I don't think French women are slimmer because they smoke and I see it as a lame excuse.
We don't eat fried food every single day, be it the chips, the crisps, fried fish or meat, fried bacon , fried eggs, we don't eat in the street or the car. We don't carry food around, don't eat in between meals, or in front of the tv, we eat at a table all together.
I also don't agree with the PP saying that now the variety is bigger. I don't see variety here. People eat the same 10 meals over and over. There is no difference according to the seasons, the same 5 or 6 veggies max during the week (cucumber, lettuce, tomato, broccoli, brussel sprouts), no artichokes, asparagus, fennel, celery, green beans, radicchio, ...very often a meal on a French doesn't have a name, it is a steak, chicken breast, a fish cooked in a pan, with 2 veggies (one cooked, one salad) and maybe some potatoes, not flooded with an artificial sauce, yes the meat will be cooked with a knob of butter, cracked pepper and crystal salt. That's it. We eat soups, salads from the toddler years, the grated carrot salad is a French classic.
When in season we will eat mussels or clams, but also pasta with eggplants, or a tuna sauce.
It doesn't take ages to cook, but then we don't eat at 5 or 6pm, but around 7.30 - 8.
And if we can avoid it, we never have a sandwich at lunch. We will sit in a cafe having the menu du jour. Here people eat sandwich every single day of the year, with artificial cheese, poor quality processed meat, and fake spreadable butter.
I bake quite a lot, a cake will last 3 days, kids have a slice for breakfast and one for afternoon tea. Sometimes if a friend comes over for coffee, I will have one myself so my guest doesn't feel awkward , but usually not. I don't crave cakes or snacks.
It is the whole culture or lack of culture around food that is to blame, from the baby years, not the cigarette.