Several fat-soluble compounds such as cholesterol and fat-soluble vitamins have important physiological activities in the body, and their excess and/or deˆciency have been reported to be closely associated with the onset and progression of several conditions such as lifestyle-related diseases. It is important to clarify not only the physiological activities but also in vivo kinetics of fat-soluble compounds to understand their in vivo activity (toxicity). This review introduces our recent (reverse) translational research in a combination of basic and clinical studies to reveal the regulatory mechanisms of in vivo behaviors of fat-soluble compounds and eŠects of their disruption in humans.