Cardiometabolic disease (e.g., type 2 diabetes or cardiovascular disease) is a leading cause of disability and mortality in the United States, and especially so among Veterans. Posttraumatic stress disorder (PTSD) – a salient health concern for many Veterans and their families – is linked to an increased risk of cardiometabolic disease and premature mortality. The precise mechanisms of this relationship are not fully understood. However, recent research suggests that a diagnosis of PTSD increases the risk for hypertension, dyslipidemia and obesity, all of which are known predictors of cardiometabolic disease. A better understanding of what modifiable factors (e.g., lifestyle) influence the link between PTSD and cardiometabolic health and functioning will aid in the development of novel rehabilitative nonpharmacological interventions (e.g., exercise) for cardiometabolic disease and disability in Veterans with PTSD. Physical activity (PA) and diet are promising examples of modifiable lifestyle factors. For instance, regular PA and a healthy diet strongly reduce the risk for cardiometabolic disease through numerous pathways, such as reductions in blood pressure, blood lipids, adiposity, and by promoting blood glucose control. Simply put, 80% of all new cases of type 2 diabetes are attributed to physical inactivity and poor diet. Low cardiorespiratory fitness (CRF) is also a critical factor in the risk for disability and mortality due to cardiovascular disease. Despite the clear value and potential impact, there is little research examining relationships between PA and diet, cardiometabolic health, and functioning in Veterans with PTSD. This is a critical research gap. Physical inactivity and poor diet increase the risk of cardiometabolic disease and PTSD likely compounds this risk. Veterans with PTSD often lead sedentary lives and make unhealthy dietary choices placing them in a perfect storm for developing cardiometabolic disease and related disability. The purpose of this project is to examine the influence of several modifiable yet understudied lifestyle factors (i.e., PA and diet quality) on indicators of cardiometabolic health, and functioning in post-9/11 Veterans. The aims of this project are: Aim 1: To examine PA participation as a mechanism linking PTSD to cardiometabolic health and functioning in post-9/11 Veterans. I will longitudinally assess associations between PTSD diagnosis, PA, cardiometabolic health, and functioning over time in 250 TRACTS participants. H1-1: Total self-report PA will mediate the effects of PTSD on cardiometabolic health and functioning over time, such that lower PA will increase the detrimental effect of PTSD on cardiometabolic health and functioning. H1-2: PA intensity will moderate the effect physical activity has on cardiometabolic health and functioning. Supplemental Aim 1A: To validate the use of a self-report clinical measure of PA against objective measure obtained via accelerometry. Objective measurement o...