New Perspectives on the Old Uses of Traditional Medicinal and Edible Herbs: Extract and Spent Material of (L.) Delarbre.

(L.) Delarbre, commonly known as water pepper, possesses multifunctional potential. Our research focuses on its complex phenolic composition, bioactivity, safety evaluation and utilization in a sustainable manner. Moreover, a survey was conducted among the Serbian population to gain insight into the attitude towards traditional wild-growing herbs (i.e., ), the level of familiarity with their zero-waste culture, and to assess eating behaviors. A survey was conducted with 168 participants to assess attitudes towards traditional herbs, zero-waste culture, and eating behaviors, while cytotoxicity, in vivo toxicity, chemical analysis of secondary metabolites, and probiotic viability assays were performed to evaluate the effects of the PH extract. Notably, extract (PH) exhibits a diverse phenolic profile, including quinic acid (3.68 ± 0.37 mg/g DW), gallic acid (1.16 ± 0.10 mg/g DW), quercetin (2.34 ± 0.70 mg/g DW) and kaempferol-3--glucoside (4.18 ± 0.17 mg/g DW). These bioactive compounds have been linked to anticancer effects. The tested extract demonstrated a cytotoxic effect on the human neuroblastoma cell line, opening questions for the further exploration of its mechanisms for potential therapeutic applications. Based on the toxicity assessment in the model, the PH could be characterized with good safety, especially for the lower concentrations (LC = 0.83 mg/mL, 24 h). The utilization of the spent PH material supports the viability of psychobiotic strains (up to 9.26 ± 0.54 log CFU/mL). Based on the conducted survey, 63.7% ( = 107) of respondents mainly prefer traditional instead of imported herbs. The respondents were skeptical about zero-waste edibles; 51.2% ( = 86) would not try them, and a bit more than half were not familiar with zero-waste culture (57.7%; = 97). Only 8.3% ( = 14) followed a flexitarian diet as a dietary pattern. The use of underutilized traditional plants and their spent material could potentially contribute to the acceptance of a zero-waste culture in Serbia. Reinventing the use of neglected traditional plants and addressing ways for spent material valorization could contribute to the acceptance of a zero-waste strategy and encourage healthier eating behavior.