Food of today has diminished nutrients in comparison to food prior to industrialized agricultural practices.
Due to mono-cropping, poor animal feeding processes, and the use of herbicides, soil contains fewer and fewer nutrients and that void is passed onto us through our food. While foods still have the same number of calories, the vitamins and minerals that you consume with those calories are much less than when your grandmother was eating the same foods.
Davis, D., Epp, M, & Rjordan, H. (2004). Changes in USDA Food Composition Data for 43 Garden Crops, 1950-1999. Journal of American College of Nutrition; 23(6):669-82