Click here if you missed the overview of Nutrient Density
Dr. Donald R. Davis took a look at the data and found declines all over the place. (This is all summarized in layman’s terms in an article by Viki Godal on Organic Authority’s website). Here’s an excerpt from his results page:
Group Changes Between 1950 and 1999
We evaluated the moisture-adjusted ratios of USDA nutrient contents, R = 1999/1950, for 13 nutrients plus water, usually in 42 to 43 foods. Considered as a group, these foods show apparent, statistically reliable median decreases between 1950 and 1999 for all 3 of the minerals evaluated: Ca (–16%), P (–9%)and Fe (–15%). However, the median ash content (a robust measure of major minerals, mainly K) decreased by only 6%, not reliably different than zero (p = 0.22). Two of 5 vitamins show apparently reliable median decreases: riboflavin (–38%)and ascorbic acid (–15% before adjustment; see below). Median protein content apparently dropped slightly (–6%). There were no detectable median changes for vitamin A (28 foods), thiamin, niacin, fat, or carbohydrate.