The majority of people report eating highly palatable, calorically-dense ?comfort? foods as a means of stress relief. Indeed, individuals with a history of eating palatable foods have improved mood and reduced physiological and emotional responses to stress. However, comfort feeding comes at a significant cost to metabolic health, as stress-related eaters have higher BMIs and have more difficulty losing weight. Despite clear evidence that comfort feeding is a primary cause of obesity for many people, we know very little about why this is the case. This proposal addresses two critical gaps in our knowledge. First, it determines the mechanisms by which comfort feeding gives stress relief in normal weight individuals. Second, it identifies the extent that this stress relief is impaired during diet-induced obesity (DIO). This has important health implications, as it suggests a vicious cycle whereby obese individuals continually increase their consumption of palatable foods to maintain effective stress relief at the cost of worsening metabolic health. We propose to study these relationships using a palatable ?snacking? paradigm in which rats are given twice-daily access to a small amount of palatable sucrose solution, or water as a control. Rats given this limited sucrose intake (LSI) paradigm reduce their chow intake to compensate for the calories in the sucrose and maintain normal body weight, allowing us to isolate the mechanisms by which LSI reduces stress responses in normal weight individuals. Indeed, LSI rats have attenuated neuroendocrine (HPA axis), behavioral, and metabolic (energy mobilization) responses to a stress challenge. Moreover, LSI is unable to provide stress-blunting in DIO rats, suggesting that obesity may increase the amount of palatable food needed to obtain stress relief. The LSI paradigm therefore provides the unique opportunity to determine the mechanism underlying effective stress relief in normal weight rodents, how these mechanisms are disrupted by DIO, and whether DIO escalates sucrose intake thereby restoring effective stress relief at the cost of worsening metabolic health. Furthermore, our prior work implicates the basolateral amygdala (BLA) as a key site for LSI stress relief, though the intra- BLA mechanism that mediates this stress-blunting is not known. Our new preliminary data point to endocannabinoids (eCB; endogenous marijuana-like molecules) acting within the BLA as this mechanism. For instance, restraint stress rapidly increases BLA eCB (anandamide) content in LSI rats, but not water controls, and eCB signaling in the BLA is known to blunt stress responses. This proposal therefore addresses the hypothesis that palatable foods curb stress responses by increasing eCB signaling in the BLA during stress. The proposed experiments determine the contribution of BLA eCB-signaling to LSI stress relief in vivo, and to post-stress neuronal function and plasticity in BLA slices in vitro. Experiments also determine the extent to which DIO interferes with BLA eCB signaling after LSI, as well as the ability of escalated sucrose consumption to recover BLA eCB signaling and stress-blunting during DIO.
Most people report eating tasty, high-calorie ?comfort? foods to help relieve stress, but this stress-eating promotes obesity and thwarts weight loss interventions. This project seeks to understand how eating tasty foods curbs stress, and further asks if this stress relief becomes less effective in obesity. This has important implications for health, as it suggests a vicious cycle wherby obese individuals continually increase their comfort food consumption in order to maintain effective stress relief, at the cost of worsening metabolic health.
