Several studies over the past few years have found that there has been a decline in the nutrient levels of fruit and vegetables over the past few decades. The USA Department of Agriculture found in 2004 that 43 garden crops had had statistically significant declines in protein, calcium, potassium, iron, copper and vitamins B2 and C, with some nutrient values 40% lower in modern plants.
While others, especially permaculturists have pointed the finger at increased use of chemicals or a need for soil remineralisation, the leader of the study at the time concluded that it was actually our preference for growing higher yielding varieties that was causing the decline.
Decades of plant breeding for faster growth, bigger plants, tighter heads on broccoli and cabbage, larger capsicums, and more potatoes per plant create a dilution effect, where the nutrients are spread over more kilos (or pounds) of produce.
It looks like the answer is to not seek out and grow those varieties that promise high yield or even bigger fruit – and, of course, to eat even more fresh vegetable and fruit.