Abstract Controlled feeding studies have been useful in assessing the relationship between isotope values from dietary sources and consumer tissues. We report the organic oxygen and hydrogen values of animal tissue from a porcine controlled dietary study. A complex mixture of fractionation and incorporation is revealed. In both δ D and δ 18 O, differences in the absolute values and the amount of variation between and within consumer tissue are documented. Significant differences in δ D and δ 18 O are observed between protein sources such as keratin and collagen. Copyright © 2008 John Wiley & Sons, Ltd.