A thorough quality assurance (QA) program upholds the integrity of nutrition research studies by yielding reliable data and results. Continually evaluating the implementation of a procedure against a goal and making adjustments when needed enhance the quality of a study's conduct and outcomes. Controlled diet studies require QA processes at various steps beginning with the screening of study participants, through diet preparation and delivery to data collection. Staff training and observations with monitoring activities, are important so tasks are completed according to protocol. When several clinical sites participate as partners in a controlled diet study, uniform procedures must be followed and a formal standardized QA program will assist. The Dietary Approaches to Stop Hypertension (DASH)-Sodium study employed such a program, described in this article, that included training staff, observing procedures, monitoring data for completeness and accuracy, evaluating processes, giving feedback, and documenting that tasks were done according to protocol. Furthermore, QA processes were used in the areas of participant screening, orientation, diet adherence, food procurement and preparation, and exit interviews. Other researchers may implement similar activities to ensure quality in their nutrition research programs.