Compound-specific isotope analysis of amino acids in human collagen from Yuzhniy Oleniy Ostrov reveals δ¹³C essential amino acid profiles that are nearly identical to those of freshwater fish (zander and vendace), demonstrating that aquatic resources constituted the primary protein source in the diet, rather than terrestrial plants or game, despite model-estimated high plant intake.

When people eat fish, the essential amino acids in the fish's proteins pass into their bodies unchanged. These amino acids carry a unique carbon fingerprint from the algae and bacteria at the bottom of the lake food chain. The body uses these amino acids to build collagen in bones and teeth, so the carbon signature in the collagen matches the fish, not plants or land animals. Nitrogen in the collagen also becomes heavier because the body gets rid of excess nitrogen from eating lots of protein, leaving behind more of the heavy nitrogen isotope.