Part 30 includes just two supplements: potassium and prebiotics. The role of potassium in exercise metabolism has been well documented in the literature but it seems that its appearance as a component of electrolyte-replacement products is a custom, rather than a necessity, since it is widely found in the diet. By contrast, prebiotics are at the beginning of an investigative story which may conclude by finding some beneficial uses for athletes to promote immune or gastrointestinal (GI) health during times of increased stress.