Dietary transition to an Indigenous Greenlandic diet induces instant shifts in gut microbiota composition – a pilot intervention study

Introduction Non-Western diets are increasingly studied for their relationship to gut microbiota composition and diversity, although most research in this area has focused on plant-based, fiber-rich diets. Here, we present a single-participant longitudinal study investigating gut microbiota dynamics during a transition from a Western diet to a 12-week Indigenous Arctic animal-based diet composed of minimally processed raw, dried, and fermented animal-source foods. During one month of this period, the participant consumed dried whole fish ( ammassak ), including intestinal contents, representing a form of gastrophagy, a practice common to the Arctic diet, that may increase exposure to food-associated microbes. Methods Fecal samples (n = 29) were collected before, during, and after the Arctic diet phase. 16S rRNA gene sequencing of the V3-V4 region was used to profile bacterial communities. Diversity metrics, Firmicutes/Bacteroidota (F/B) ratios, and taxonomic composition analyses were performed to assess compositional shifts across diet phases. Results Alpha diversity remained relatively steady throughout the study, with a tendency toward higher values during the Arctic diet. The F/B ratio increased from 1.31 to 2.12 during the Arctic diet phase and remained elevated (2.38) after returning to a Western diet. Beta diversity analysis revealed significant restructuring of the gut microbiota at the onset of the Arctic diet, followed by partial reversibility upon returning to a Western diet. Fiber-associated taxa like Prevotella 9 disappeared, and Bifidobacterium declined, while protein- and fat-associated taxa, including Bacteroides , Lachnoclostridium , and Alistipes , increased. Several genera appeared during the Arctic diet phase that were absent during the preceding Western diet phase, consistent with altered microbial exposure. Among those, Photobacterium was also detected in the ammassak, suggesting potential microbial exposure during the gastrophagy period. Discussion These results provide preliminary evidence that the gut microbiota can shift substantially during an Indigenous Arctic dietary transition. Because the Arctic diet also substantially overlapped with sustained high physical activity, the observed changes should be interpreted in the context of a combined dietary and lifestyle transition. These findings highlight the need for a better understanding of underrepresented dietary patterns, such as those of Arctic Indigenous communities, and their relationship with the gut microbiota.