Some industrial pipelines have a sharp pipe diameter reduction such as that found in an orifice flow meter or at the inlet zone of certain equipment. For such processes some researchers have claimed that particle breakage occurs just before the contraction though not after it. In the present work we studied the breakage of whey protein aggregates in a sharp pipe diameter contraction and in a smoother one. CFD was used to model the flow field in both contraction types at different bulk fluid velocities. The CFD simulation results coupled with the experimental data concluded that the pipe contraction type has a strong influence on the particle breakage and the particle size reduction occurs along the entire pipe length and not only in the contraction region. The experimental results show that at the same mass flow rate more particle breakage occurs for the sharp transition than for the smoother one and that the particle size reduction is a function of both the mass flow rate and the exposure time. The CFD simulation results show that at the same mass flow rate there are important variations in the flow field between sharp and smooth transition, e.g., the turbulence eddy dissipation rate (ε) for sharp transition is much higher than for the smoother one. It was observed that for sharp transition there is a region with very high eddy dissipation rates that starts just before the contraction and remains for 5 mm after it, while for smooth transition this region is practically avoided. This difference in ε can lead to more particle breakage and it was used to explain our experimental results.