Carbon and nitrogen stable isotope analysis of bone collagen from Mesolithic human individuals of the Iberian Peninsula typically reflects a substantial contribution of terrestrial resources, with variability likely related to environmental contexts. Unfortunately, bulk collagen stable isotope analysis lacks the necessary resolution to quantify dietary components or detect low, but still significant, marine consumption, a fact that could bias the dietary reconstruction of Mesolithic people. Carbon and nitrogen isotopic analysis of single amino acids offers a more direct means to discriminate different dietary sources, in particular marine from terrestrial sources of protein. By applying multi-isotopic statistical models, we can improve quantitative estimations not only of protein but also of caloric intake, as well as exploring levels of protein in diets and their socio-ecological implications. 

Here we present the many possibilities of Compound Specific Isotope Analysis of Amino Acids (CSIA-AA) to offer an unprecedented insight into the dietary reconstruction of the Mesolithic site of El Collado (Spain). Results will certainly shed light on the proper proportion of marine resources that this population, inhumed in one of the most impressive shell-middens of the NE Iberia, consumed on a regular basis.