Similar to Japan
Your experience in France is similar to what we see in Japan. Perhaps it is a trait of the food cultures? Japanese have small servings and are taught to eat until they feel 80% full. The theory is that the “fullness” signals from our stomach take a while to activate, and if we stop eating at 100% then our stomach is overfull.
The smaller plates and more walking relates my simplistic advice about starting out on a healthier path — which is to eat 20% less and exercise 20% more. Simplistic I know, although it worked for me. Use smaller plates and fill them to the same edge of the plate as your old larger ones. Walk more and take the stairs. Little things add up. Then start exchanging the fake food for real food.
Gradually, you are in a new stream of feeling better about food and yourself.
Thanks for the insights.