In the Maya lowlands of Belize, carbon and nitrogen data from collagen have been analyzed from ten sites. The average C13 collagen values are -12.6 ± 1.2 per mil, indicating that C4 sources made up 50% of the ancient Maya diet. These average values change very slightly in the Early, Late, and Terminal Classic periods, with averages of -11.3 ± -2.3 per mil. In the Peten region, Preclassic values for collagen C13 average -10.2 ± -1.2 per mil, indicating that C4 sources made up 70% of the ancient Maya diet in this region. These differences in the region may be attributed to the greater access to marine and aquatic resources in Belize. As discussed earlier, there is evidence that marine animals were being brought alive to inland sites by means of river waterways. Areas of the Peten and the Yucatán may have been too far away from coastal regions for this concept to be utilized.