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Brazil nuts

These rich, creamy nuts are high in protein, healthy fats, and selenium, a mineral that's essential for proper immune function and may help guard against infections and flu. In a 2001 study, University of North Carolina researchers found that mice infected with the flu virus showed higher levels of inflammation if they were deficient in selenium.

Your body only needs a small amount of selenium, though, and getting too much may actually raise your risk for certain diseases. Just one nut contains more than a day's recommended value, so eat these treats sparingly.

Next: Carrots and sweet potatoes