Came across this nifty infographic at Matt Yglesias' blog. The interactive version is here at Civil Eats. The infographic shows the daily available calories in the American diet, adjusted for food that is not eaten. In other words, they measure how much food is produced, subtract the food that is wasted, and come up with the per-capita number, assuming that what's not wasted is eaten. Go to the USDA site for more information on this way of measuring the American diet.
The added fat seems to be the greatest change. A follow-up question is, where is this added fat coming from. I need to look more closely at the numbers but if I had to bet on it, I'd say that cheese is the number one culprit. Here's the chart from the USDA on the daily calories of cheese consumption over the years.