Donald R. Davis, a former research associate with the Biochemical Institute at the University of Texas, Austin, claims the average vegetable found in today's supermarket is anywhere from 5% to 40% lower in minerals (including magnesium, iron, calcium and zinc) than those harvested just 50 years ago. [Eating Your Veggies: Not As Good For You?, (Time)]

His study, published in the February 2009 issue of the Journal of HortScience, points to the genetic dilution effect and earlier harvesting -- both results of industralized agriculture where yield is created at the cost of nutrients.  While we have larger produce than ever, the product themselves actually contain less nutrients than ever.

The genetic dilution effect happens when breeding to increase crop yield.

Because nearly 90% of dry matter is carbohydrates, "when breeders select for high yield, they are, in effect, selecting mostly for high carbohydrate with no assurance that dozens of other nutrients and thousands of phytochemicals will all increase in proportion to yield."

This has led to declines in protein, amino acids, and minerals.

Additionally, modern crops are being harvested faster, which means the product has less time to absorb nutrients from synthesis or the soil. Some minerals in chemical fertilizers and pesticides also inhibit nutrient absorption and creation (plants that have to battle the elements produce healthy chemicals). Monoculture farming practices often lead to soil-mineral depletion, which affects the nutrient content of crops as well.

More and more the evidence shows that the bigger and faster options are unhealthy and destructive.