The current understanding of the mechanisms underlying the fat mimicking properties of fat replacers, such as microparticulated whey protein (MWP), is limited. MWP is known to provide fat-related mouth-feel in specific foods, such as yoghurts and cheeses. Tribological and rheological properties are well known to contribute to the perception of fat related sensory attributes. This study investigated the tribological and rheological properties of MWP in liquid and semi-solid model foods to reveal the mechanisms underlying the fat mimicking properties of MWP. In liquids, addition of MWP reduced the friction coefficient effectively. After scaling out the impact of viscosity on lubrication, results provide strong evidence that the reduction of friction of MWP in liquids is mainly due to ball-bearing lubrication. In semi-solid gels, addition of MWP also decreased the friction, but to a smaller extent compared to liquid model foods. The mechanism underlying the lubrication behavior of multi-component semi-solid foods that contain fat droplets, emulsifier, fat replacers such as MWP embedded in a gel matrix is complex. We conclude that different components affect the lubrication properties of the composite food through different mechanisms. Fat droplets reduce friction due to the formation of a fat film following a plate-out mechanism. We suggest that emulsifiers influence the formation of a fat or emulsifier film, whereas MWP is suggested to reduce friction due to a ball-bearing mechanism. In addition, the influence of bulk viscosity, gel fracture behavior, and the interactions between the MWP and its surrounding matrix and emulsifiers, need to be accounted for.