A Kushi Institute analysis found that the nutritional value of fresh vegetables had declined between 1975 and 1997. The analysis found that calcium levels dropped 27%, iron levels 37%, vitamin A levels 21%, and vitamin C levels 30%. 
Factors contributing to nutrient decline
Monoculture: Growing only one type of crop depletes the soil of nutrients. 
Pesticides: Pesticides can destroy the balance of soil microbial populations. 
Synthetic fertilizers: Fertilizers can impact the quality of food. 
Soil erosion: Soil erosion washes nutrients away from farmlands. 
Higher crop yields: Higher yields mean nutrients from the soil must be distributed across a greater volume of crops

A carefully designed White world replaced by a rat utopia