As others have already said - Portion size!

It really amazed me that US portions are like European serving platters and that is no exaggeration.

Normal plates in the Eu and Aus are around 20-23cm - In the US I have seen plates as big as 34cm across and they are piled with food. I don't know how someone eats 3 x meals a day at that size.

Asia is another good example - They do eat noodles/rice but the portion is much smaller and the ratio compared to meat and veggies is different than say if you went and bought Japanese take away in the US.