A whey-based puffed snack food was produced on a twin-screw extruder to determine the effect of varying starch type (normal corn and pregelatinised waxy), protein type (regular and instantised whey protein concentrate) and protein concentration (16%, 32% and 40%) on the physical and chemical characteristics of an extruded-expanded snack food. Increasing protein concentration and normal cornstarch significantly reduced extrudate expansion ratio, air cell size, water solubility index and increased extrudate density, and breaking force. Protein concentration and starch type significantly affected the water absorption index and water-soluble carbohydrate. Total soluble protein was influenced by protein concentration and the interaction of starch type and protein type. With normal corn starch, a covalent complex between amylose and protein was likely formed while protein:protein interactions were favoured with low pregalatinised waxy starch concentrations.