Crop yield and farming systems affect the nutritional value of plant foods

Three kinds of evidence will be presented that plant foods in the United States and the United Kingdom have lower nutritional value now than they did a half-century ago. The declines appear to be caused mainly by “dilution effects” resulting from large increases in crop yields. Environmental and genetic dilution effects occur when the increased bulk of a crop is not matched by equal increases in the synthesis or uptake of nutrients. Historical food composition data suggest median declines of at least 5% to 30% in the concentrations of protein and about half of the minerals and vitamins studied. Recent comparisons of conventional with organic fruits and vegetables have found roughly 30% higher average levels of beneficial phytochemicals in organic crops. Both conventional and organic farmers are paid primarily by their yield, so for several decades there have been intense efforts to increase crop yields. As we learn more about the effects of yield and farming systems on food quality, plant breeders and farmers may shift their priorities toward increasing nutritional value. Meanwhile, consumers concerned about nutrient declines need to become more concerned about post-harvest refining losses associated with major staple foods (added sugars, added fats and oils, and milled grains). These post-harvest losses are much broader and deeper than historical declines in nutrients. There is much that consumers can do now to improve their diets, by eating more of our current fruits, vegetables and whole grains and less of the badly depleted staples.