Yogurt

The "good" bacteria in yogurt - known as probiotics - make an essential contribution to a healthy immune system. The stomach and intestinal tract contain more than 500 different varieties of bacteria, and probiotics help maintain a balance between the good and bad bacteria by crowding out pathogens and preventing them from attaching to gut walls. Probiotics also feed on nondigestive fibers called prebiotics, producing short-chain fatty acids that decrease acidity in the colon. The decreased acidity makes the colon uninhabitable for most infection-causing pathogens, which, in turn, allows for increased mineral absorption. Research suggests that probitocs can also enhance the body's immune response by increasing levels of key players, says Beth Reardon, RD, an integrative nutritionist at Duke Integrative Medicine, North Carolina, including natural killer cells. Studies from the University of California have shown that yogurt specifically helps the body build a protein called gamma interferon, which aids the body in developing white blood cells.