I think a lot of it really has to do with eating habits and type of fod ratrn.

Astudy was done in various countries and it was shown that Americans consumed more high fat meals than any other country. Part of this is because of the pace of life we lead, always on the go and fast food is our friend.

Also a majority of Americans don't do labor intensive jobs like they used to either. Technology has made many of those jobs obsolete anymore.