They found ibex adipose tissue as the most likely fat source. Half the stomach contents were composed of adipose fat. They expected the high-fat diet because of the extreme alpine environment where the Iceman lived and was found.
"The high and cold environment is particularly challenging for the
human physiology and requires optimal nutrient supply to avoid rapid
starvation and energy loss," said Albert Zink, who also participated in
the study. "The Iceman seemed to have been fully aware that fat represents an excellent energy source."