Changes that have occurred over the past century
Food has been optimized for calories, color, ability to appear fresh for a long time, ease of harvest, but never optimized for nutrition
Food typically highly processed - often significantly reducing the vitamin content
Fertilizers - synthetic and incomplete have produced food with less vitamin content
Use of pesticides have created crops which do not have their own pesticides (i.e. far less resveratrol, etc. now)
People eat far more "empty calories" than before - depleting the nutrients which they get from good food
Farmed fish - far less fatty acids, and 1/3 as much vitamin D.
Factory Farms - where the animals are not free-roaming - getting far less of the trace elements and have no ability to influence their diet
I have some good documentation to back up many of the above points, but not enough time to include it just now
Henry Lahore August 2010