From the USDA's Dietary Guidelines for Americans, http://www.dietaryguidelines.gov/DGAs2010-PolicyDocument.htm
I am fascinated by this chart, and I’m not sure what to say about it except “sounds about right.”
At first glance it looks like folks are getting most of their calories from grain and chicken which, environmentally-speaking, is pretty good! I imagine there’s a fair bit of red meat concealed in the ‘pizza,’ ‘taco,’ and ‘pasta’ categories, though.