Project Summary/Abstract We are seeking to acquire a Delta Q Isotope Ratio Mass Spectrometer (IRMS) along with its peripherals for the UW Isotope Ratio Laboratory. The need for this instrument arises because our current Delta Plus and Delta V instruments are obsolete and no longer, or soon to be no longer, supported by the manufacturer and pose extreme challenges in terms of operability and repairs. The upgraded Delta Q IRMS is a versatile and high- performance instrument that accurately measures stable isotopic ratios in both gaseous and solid samples. Its enhanced capabilities and efficient sample analysis per isotope will ensure the continuity of our lab's operations. Specifically, this instrument will play a vital role in measuring stable isotopic ratios of hydrogen and oxygen, with a specific focus on doubly labeled water studies. These studies are of utmost importance in the fields of nutritional sciences and obesity research. The precise measurements and advanced technology of the Delta Q IRMS will provide reliable data for investigating energy balance components, thus making a significant impact in the obesity field. Accurately measuring energy intake and expenditure is crucial for comprehending human energy balance, and the doubly labeled water method stands out as the most precise approach for this purpose [1]. Conventional methods that rely on self-reported data through diet records and questionnaires are susceptible to errors and bias[2], while the doubly labeled water method, coupled with changes in body energy stores, has been advocated by Ravelli and Schoeller, 2021 [3]. As a result, the doubly labeled water method, which relies on isotope ratio analyses, is indispensable for understanding energy balance, preventing obesity and chronic diseases, and also addressing malnutrition [4]. Access to isotope ratio analyses is limited to a few expert labs worldwide, and our lab has been at the forefront of pioneering the doubly labeled water method for the past 25 years [5]. We have provided analyses to 28 investigators leading to 107 publications, which have been cited more than 47,000 times. To continue meeting the demands of our NIH-funded users, the acquisition of the Delta Q IRMS is indispensable. It will (1) provide precise and accurate isotopic ratio measurements, enabling in-depth exploration of energy expenditure, energy intake, body composition, and metabolic pathways in humans and animals, (2) enhance the health-related goals of our users' investigations, and (3) foster biomedical research within and beyond our institution. The acquisition of this instrument is vital for cutting-edge research and its availability in the UW Isotope Ratio Lab will have a profound impact on the scientific community. Ensuring the continuous generation of accurate data will enable valuable insights and advancements in diverse research areas that rely on stable isotope analyses. Moreover, it will empower researchers to make significant strides in vario...