Gaultheria Berries as Potential Functional Foods: Phytochemical Composition, Health-Promoting Properties, and Nutritional Potential

Background/Objectives: Gaultheria L. (Ericaceae) berries are edible wild fruits traditionally consumed in several regions of Asia and the Americas and used in folk medicine for the management of fever, pain, inflammation, and digestive disorders. In recent years, they have attracted increasing attention as prospective sources of phytochemicals with potential biological activity and as candidate ingredients for future food applications. This review aimed to critically evaluate the current knowledge on the nutritional value, phytochemical composition, biological activities, and functional food potential of Gaultheria fruits. Methods: A comprehensive literature review was conducted using major scientific databases (Web of Science, Scopus, PubMed, Google Scholar, and ScienceDirect) to identify studies investigating the chemical composition, nutritional constituents, biological activities, and potential applications of Gaultheria berries. Published evidence from phytochemical analyses, cell-free assays, cellular models, and available nutritional studies was critically assessed and comparatively summarised across different Gaultheria species. Results: Available evidence indicates that Gaultheria berries are rich in polyphenols, including anthocyanins, proanthocyanidins, flavonoids, hydroxycinnamic acid derivatives, and chlorogenic acid isomers, together with characteristic salicylate glycosides, iridoids, volatile methyl salicylate derivatives, vitamins, and mineral elements. Experimental studies, predominantly performed in vitro using chemical and cell-based models, provide preliminary evidence of antioxidant, anti-inflammatory, antimicrobial, anti-diabetic, neuroprotective, photoprotective, cytoprotective, antiproliferative, dermatological, and enzyme-inhibitory activities. Despite these promising findings, comparative investigations across species remain limited, and evidence regarding bioavailability, metabolism, mechanisms of action, and clinical efficacy remains insufficient. Conclusions: Current evidence suggests that Gaultheria berries represent underutilised sources of structurally diverse bioactive compounds that warrant further investigation as potential food and nutraceutical ingredients. However, their health-promoting effects in humans remain unestablished. Future research should prioritise comprehensive metabolomic profiling, standardisation of phytochemical composition, bioavailability and safety assessment, in vivo validation, and controlled human studies before specific health benefits or therapeutic applications can be substantiated.