Comment by jdietrich

The obvious answer is more calories. The obvious answer for why more calories is pretty obvious to non-Americans - your portion sizes are crazy, albeit everyone else in the world is catching up. Even if you buy a "healthy" meal in a quick service restaurant or as a pre-packaged retail product, the smallest portion size is still likely to be grossly excessive.

The obvious answer for why portion sizes are increasing is that food keeps getting cheaper, in particular relative to other costs in the food service industry. The traditional formula for restaurant pricing is 1/3 ingredients, 1/3 labour and 1/3 overheads; if your food costs have decreased over time but your rent and labour costs continue to increase, it's natural to increase portion sizes to maintain the appearance of value-for-money. The same would apply (to a moderately lesser extent) to convenience foods sold at retail. This has a quite drastic anchoring effect - when you normalise excessively large portions, reasonable portions seem meagre.