In physiology, to act as an intermediary that carries or transfers a substance, signal, or effect between different parts of the body. Hormones mediate communication between organs, neurotransmitters mediate signals across synapses, and carrier proteins mediate the transport of nutrients across cell membranes. In nutrition science, researchers describe how dietary components mediate health effects: for example, fibre mediates cholesterol lowering partly through bile acid binding. Understanding mediation helps explain chains of causation, distinguishing direct effects from those operating through intermediate steps. The concept is central to interpreting how foods and nutrients influence complex bodily systems.