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Average retail price per pound: $3.41

Mushrooms have been used for centuries in various medicinal remedies. They help to increase the production of white blood cells, which help fight off infection. Choose shiitake, maitake and reishi varieties for the biggest dose of immunity. Surprisingly, they are a good source of Vitamin D. A cup of chanterelle, morel, shiitake or Portobello provides about 400 IUs, or 65 percent of DV.