Epistemic understanding of science is essential for critical evaluation of scientific claims. In principle, developing students' epistemic understanding would enhance students' capability in evaluating scientific claims. However, findings on this "expected" connection have been inconclusive. This paper seeks to examine this discrepancy between epistemic understanding in theory, and the practical application of this understanding. It uses the concept of "adherence" from the literature on conceptual change when accounting for this discrepancy. Questionnaires were used to examine adherences to epistemic understanding in evaluating health-related claims by 42 college-level nonscience majors. Follow-up interviews were conducted to explain their adherences to epistemic understanding during their evaluation. The analysis revealed that: (a) Students tended to adhere to process of inquiry much stronger than the nature of scientific knowledge and the social context of science. (b) Students' low adherence to the nature of scientific findings and generation process was found to relate to an interplay among various epistemic aspects of science. (c) Students demonstrated low adherence in practicing epistemic understanding due to difference in contexts between giving declarative statements "about" science and using epistemic understanding to evaluate scientific claims. These findings have theoretical implications on the discrepancy between theory and practice in relation to the role of epistemic understanding of science, and on what constitutes informed epistemic understanding. They also have practical implications in terms of enhancing students' adherences to epistemic understanding in evaluating scientific claims.