BIG Mac is not bigger than I expected

American BIG Mac is not bigger than I expected. It looks same as that in Japan. However, it is usually enough for my stomach. Even though I think that it is not enough soon after eating, the feeling of fullness lasts for a long time. Does it have a trick for our fullness? Fundamentally the taste of burgers and fried potato in America is same as that in Japan. People say the taste of MacDonald products is not different around the world. I also think so. The taste of MacDonald is always at between "very good" and "bad".