I dont feel like they are. Traveling France and Italy a couple years back, I found myself not finishing meals much more regularly that I do in the states, Even though I was eating a bit more because I was walking 5+ miles a day.

Maybe i was in part over ordering due to language, or menu expectations. Maybe some of thw places I was in were touristy and over doing it to match 'american portions'

But for instance, i got breakfast that was 'oefs en cocotte de compagne' at a café a couple blocks from the louvre, far enough to not be in the tourist trap surrounding area anymore.

It was massive- 4 shired eggs with a generous amount of mushrooms and gruyere, served with 4 pieces of toast. And I confirmed with the waiter that that was not a shared portion....