At a diner on the rez to the north of us on Labor Day, the tsuma, onechan, imoto, and I were able to finish exactly half of the two pancake meals we ordered (one with ham and eggs on the side, one without), knowing how huge and heavy the pancakes at that place were. We spent just under $9 and still haven't finished the leftovers.
At a cheap bento place across the street from us in Fukuoka, we used to spend about the same amount of money to feed all four of us at lunchtime. Rather than just three kinds of foods, we usually got 3-5 different kinds of meats/fish, 5-7 different kinds of vegetables, and 2-4 different kinds of carb-laden things. So the volume of food was much less, but the variety of tastes and nutrients was much higher.
Perhaps this explains why we felt heavy in Japan and feel thin in the U.S.?