Our diets are crap. The combination of cash cropping and water borne sanitation ensures that the five dozen bio-essential element that are differentially extracted from soil by food crops are washed to the oceans and lost to the land.
Food grown on chemical fertilizers, which restore three to ~12 elements, has 75% lower concentration of vitamins, biol-flavenoids, anti-oxidants, immuno-support complexes. Agonomists missed this because their mission was kilos per hectare, and the other four dozen elements do not affect mass yield in laboratories ("scientific control of minimized variables").
They do, however, affect the plant immune responses to weeds, insects, moulds and worms so we now need herbicides, insecticides, fungicides and vermicides to get crops to market.
Further, the other four dozen elements were part of the mammalian exo-metabolism, our mutualistic plant species producing pre-cursors, co-enzymes and other molecules we need on occasion but can't synthesize internally. This accounts for our increased susceptibility to bacterial and viral infections, heart disease and cancer, all of which are worse now than in the 19th Century.
Anti-biotics, anti-virals, and vaccines are all symptoms of soil depletion that surrounds all cities going back to Harappa and Giza! Those and dozens more ancient civilizations than we know of collapsed due to dietary deficiencies leading to plagues and created the major deserts of this world.