A diet rich in fiber...
According to a new preclinical study by researchers from the University of Lausanne and Monash University, a diet rich in fiber blunts harmful immune responses in the lungs while boosting antiviral immunity by activating T cells; and these dual benefits are mediated by changes in the composition of gut bacteria, leading to an increase in the production of short-chain fatty acids through the microbial fermentation of dietary fiber.
http://www.sci-news.com/medicine/dietary-fiber-influenza-06009.html