Functional food plays an increasingly important role in shaping healthy dietary habits by integrating health-promoting components into consumers’ everyday diets and helping reduce food waste. Products developed using by-products and raw material streams from food processing can support the principles of the circular economy (CE) by improving resource efficiency and lowering the environmental footprint of the food system. In Poland, as in many countries worldwide, functional food is a rapidly growing category that can contribute to public health and serve as a driver of economic development. However, the excessive and scientifically unsupported use of the term “functional food” for marketing purposes may mislead consumers and weaken trust in this product group. From a CE perspective, transparent communication and informed consumer choices are essential, as they promote environmentally responsible behaviors and support sustainable production models. The aim of this study was to assess the level of knowledge about functional food among residents of Eastern Poland, which is a less industrialized and predominantly agricultural region. The analysis focused on awareness of health benefits, consumption frequency, consumer attitudes, and interest in educational initiatives promoting functional food within CE principles. The study also examined whether consumers associate functional food with sustainability-oriented practices. The findings offer insights for educational and marketing strategies grounded in scientific evidence and highlight the potential of functional food in building a sustainable, resource-efficient food system.