There was a nutritional study done on Chinese villagers some decades ago, whose diet did not seem to include enough vitamins for human health.
Sure enough, when they subjected undergraduates back in Connecticut to an imitation of that same rural diet, they got nutritional deficiencies.
It turned out that, in China, they were not washing off the veggies as thoroughly as the Yale researchers did. The small amount of soil bacteria in the small amount of soil that clung to leaves and stems provided enough vitamins for health.
"Eat dirt, be healthy!"
