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Omic, Microscopic Analysis Elucidates Otzi's Last Meal

Otzi gastrointestinal tract.

NEW YORK (GenomeWeb) – Genetic data, ancient protein profiles, metabolite analyses, and microscopy fed into a new omics-based analysis of Otzi the Iceman's final meal, revealing a fat-heavy diet of ibex and red deer material accompanied by einkorn wheat and a touch of toxic material that appeared to stem from bracken ferns.

As they reported in Current Biology today, researchers from Italy, Austria, Singapore, and elsewhere did PCR- and targeted sequencing-based analyses of ancient DNA in several stomach and small intestine biopsies that were painstakingly removed from Otzi's 5,300 year old mummified remains — originally found in the Eastern Italian Alps in the early 1990s. Together with metabolite, lipid, glycan, stable isotope, and microscopic analyses, the sequence data suggested that Otzi had an omnivorous diet made up of both animal and plant material.

"Our multi-pronged approach provides unprecedented analytical depth, deciphering the nutritional habit, meal composition, and food-processing methods of this Copper Age individual," co-first author Frank Maixner, an investigator with the Eurac Research Institute for Mummy Studies, and his colleagues wrote. "Reconstruction of past subsistence appears to be vital to our understanding of past societies."

Following from a 2011 study in the Journal of Archeological Science, which suggested that Otzi died with a full belly, the researchers turned to microscopy and their multi-'omics approaches to analyze 11 biopsies of gastrointestinal contents found in the stomach, small intestine, or large intestine.

These samples contained minerals such as iron, calcium, zinc, magnesium, and sodium, the team reported, along with trace levels of copper, selenium, and other nutrients. Some of the ancient DNA reads in Otzi's gut lined up with eukaryotic organisms, including sequences from fungi, the ibex goat (Capra ibex), red deer (Cervus elaphus), Triticum wheat, and Pteridium aquilinum fern plants from the aquilinum sub-species. Many of the reads also represented microbes that may have inhabited Otzi's gut.

Likewise, the researchers' proteomic analysis led to 167 animal and plant proteins in the stomach and gut biopsy samples. These included protein sequences that lined up with those attributed to Triticinae plants, Caprinae ruminant animals, and Cervinae deer.

"The microscopic and molecular data presented support the presence of three major components of the Iceman's last meal: fat and game meat from ibex and red deer supplemented with cereals from einkorn," the authors wrote, adding that the "pervasive presence of bracken particles" could reflect consumption of the plant, despite its toxicity, or the use of fern leaves for wrapping other food items.

There were other clues about the Iceman's last meal, too. For example, charcoal particles in the gut samples hinted that he may have used fire to prepare parts of the final feast, though the team noted that the meat he consumed could also have been smoked or slow dried based on their microscopic and spectroscopic measurements.

"Drying meat by smoking or in the open air are simple but highly effective methods for meat preservation that would have allowed the Iceman to store meat long term on journeys or in periods of food scarcity," the authors concluded, noting that the analysis pointed to a meal that was "well-balanced mix of carbohydrates, proteins, and lipids, perfectly adjusted to the energetic requirements of [Otzi's] high-altitude trekking."