Many physiological functions, such as the digestive function, are broad, complex scientific topics. Therefore, to build relevant, accessible claims about functional foods that relate to these functions, marketers need to understand what consumers know about them, in terms of the associated symptoms, diseases and health benefits. Such knowledge cannot be captured effectively through direct questioning; it requires implicit testing that can limit biases and reveal unconscious knowledge. For this study, 240 consumers were invited to participate in an implicit lexical decision task via an online platform, and their responses reveal that the concept of ‘immunity’ is associated in mothers' minds with three symptoms related to their personal experiences with their children. By measuring associations that emerge without pre-existing rational processes, this implicit measure offers a more precise picture of the semantic network for immunity, which consumers could not express explicitly in response to direct questioning. Thus the recommended protocol is not only new to market research but also adds substantial value to the tests that currently serve to dig into consumers' minds.