Table 4 of the original report gives more detailed numbers. In the period 1909-1919, grains, potatoes and sweeteners together contributed 54.4% of American calories. In 2004, it was down to 43%.
https://docs.google.com/viewer?url=http%3A%2F%2Fwww.cnpp.usd...
On the other hand, fat consumption nearly doubled over that period (from 12.6% to 23.9%).
For example, even though a cherry has much higher GI than a potato, you eat more sugar/carbohydrates in one potato than in one cherry, so a potato has higher GL and thus higher insulin response.
The "complex carb" and glycemic index thing is pretty well nonsense. A carb is a carb. The only question is whether you have a properly functioning metabolism and insulin sensitivity. They call a screwed up insulin sensitivity "metabolic syndrome". If you've developed one, typically through many years of poor eating, you need to cut out starch, because your fat cells and pancreas can't handle it properly. If you're thin, well then the glycemic index thing is useless. Your pancreas and fat cells work fine.