Declining Fruit and Vegetable Nutrient Composition: What Is the Evidence?, American Society for Horticultural Science, February 2009
Three kinds of evidence point toward declines of some nutrients in fruits and vegetables available in the United States and the United Kingdom:
1) Early studies of fertilization found inverse relationships between crop yield and mineral concentrations — the widely cited “dilution effect.”
2) Three recent studies of historical food composition data found apparent median declines of 5% to 40% or more in some minerals in groups of vegetables and perhaps fruits; one study also evaluated vitamins and protein with similar results.
3) Recent side-by-side plantings of low- and high-yield cultivars of broccoli and grains found consistently negative correlations between yield and concentrations of minerals and protein, a newly recognized genetic dilution effect.
The evidence for nutrient declines began to accumulate in the 1940s with observations of (environmental) dilution effects on minerals in many foods and diverse other plants. Recent studies of historical nutrient content data for fruits and vegetables spanning 50 to 70 years show apparent median declines of 5% to 40% or more in minerals, vitamins, and protein in groups of foods, especially in vegetables.
Recently, limited numbers of side-by-side comparisons of low- and high-yield cultivars of the same food have proven the existence of genetic dilution effects in which yield increases derive from selective breeding rather than environmental measures such as fertilization.
In fruits, vegetables, and grains, usually 80% to 90% of the dry weight yield is carbohydrate. Thus, 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. Thus, genetic dilution effects seem unsurprising.
So … as yields have increased, nutrient content has decreased.
Our bodies likely have fewer of the nutrients they need and more (a whole lot more) of the chemicals they don’t need than they did 80 years ago.
Body Burden: The Pollution In People