At the Fancy Food Show, five or six booths sold probiotic foods, usually yogurt. At each booth I asked what they could tell me about the health effects of probiotics. Mostly the question seemed to annoy them — especially the employees hired for the event.
But at the Oixos booth — Oixos is a Greek yogurt made by Stonyfield Farm, an organic dairy in New Hampshire — Amy Plourde, a graphic designer at Stonyfield, told me that for a long time she was “always sick” with sinus infections, colds, and even mononucleosis. During that time, she ate yogurt once/week. When she started working at Stonyfield she began to eat yogurt once/day (6 oz. at breakfast) and her health got much better. Stonyfield yogurt has relatively high amounts of live bacteria. Their website has a list of scientific papers about yogurt and the immune system.
My take is that our immune systems need a steady stream of foreign pathogens (e.g., bacteria) and pieces of pathogens (e.g., bacterial cell walls) to stay “awake”. When your immune system is working properly you fight off all sorts of bacteria and viruses without noticing. When your immune system isn’t working properly it overreacts (allergies) and takes too long to react (infectious diseases). Weston Price found twelve communities eating traditional diets whose health was excellent. Their diets varied tremendously but one thing they had in common was daily consumption of fermented foods, including cheese, kefir, sauerkraut, and fermented fish. This supports Amy’s story right down to the dosage. If you don’t eat fermented foods, you might use hookworms, which excrete a steady stream of foreign substances into the blood. (Thanks, Tom.) Hookworms definitely reduce allergy symptoms; I don’t think anyone has asked if they reduce colds and other infections.