Probiotics are foods or dietary supplements that contain large amounts of beneficial bacteria normally found in our lower intestines. Their health benefits over a range of health conditions are only just starting to be realised. In a recent clinical trial (Journal of Sports Nutrition & Exercise Metabolism, 2011), it was shown that endurance athletes that consumed a probiotic supplementation were 27% less likely to experience an upper respiratory tract infection for a week or longer, when compared to a control group. Also, their total number of infections were nearly half that of the control group. These results strongly suggest that daily probiotic supplementation may help to support and strengthen an immune system that is already stressed from the physical demands of the endurance athlete.