Several studies of fruits, vegetables, and grains have found a decline in nutritional value since the 1950s, partly because of soil depletion and modern farming techniques.

There is “considerable evidence” that such problems may be related to changes in cultivated varieties of fruits and vegetables that have led to high-yielding plants being less nutritious than historical varieties, The New York Times reports.

Other factors have contributed to the problem as well, including the extensive use of chemical fertilizers, and changes in food processing, and preparation. A 2004 study that evaluated Department of Agriculture data for 43 garden crops from 1950 to 1999 found statistically significant declines for six nutrients — protein, calcium, potassium, iron and vitamins B2 and C.

The researchers suggested that “any real declines are generally most easily explained by changes in cultivated varieties,” like possible trade-offs between yield and nutrient content.

They also noted fruits and vegetables are still nutritious and suggested the remedy was to eat more vegetables, fruits, whole grains, nuts and beans and less refined sugars, separated fats and oils, and white flour and rice.