Purpose <p>A vegan diet is associated with health benefits but may also lead to inadequate intake of essential nutrients. Due to the lower selenium content in plant-based compared to animal-based foods, many vegans do not reach the recommended selenium intake in Europe. The only plant-based food with high selenium content is the Brazil nut, even though there is also a high variability. Therefore, we investigated the effectiveness of Brazil nut butter compared to a dietary supplement as selenium source to improve the selenium status of vegans and omnivores.</p> Methods <p>44 vegans and 42 omnivores were randomly assigned to one of three intervention groups, either receiving placebo or consuming additional 55&#xa0;µg of selenium daily as Brazil nut butter or supplement for two weeks. Serum selenium concentrations, glutathione peroxidase&#xa0;3 (GPX3), and selenoprotein P (SELENOP) were measured at baseline and after intervention. Additionally, dietary selenium intake was estimated using a five-day dietary protocol.</p> Results <p>The estimated selenium intake was significantly lower in vegans compared to omnivores and correlated with all three selenium biomarkers. Independent of the dietary pattern (vegan or omnivore), Brazil nut butter as well as supplement significantly increased serum selenium and SELENOP concentrations, while there were no changes in the placebo groups. Both interventions were equally effective in increasing selenium levels, but the upregulation of SELENOP was more pronounced in vegans than in omnivores.</p> Conclusion <p>Brazil nuts are a plant-based source of selenium suitable for vegans and omnivores to improve their selenium status when consumed once in a while.</p> Trial registration number and date of registration <p>Clinical trials registration number: NCT05814874, April 18 2023.</p>