| Popis: |
The increased prevalence of obesity has become a worldwide problem in the last forty years (French, Epstein, Jeffery, Blundell, & Wardle, 2012; WHO, 2016). Obesity is associated with significant physical (WHO, 2016) and mental health problems (Luppino et al., 2010). From an evolutionary perspective, animals' food-seeking strategies promote the overconsumption of high-energy foods in environments where food can be scarce. Possibly, these inherited strategies are unhealthy in contemporary environments in which food is available and its energy costs low, promoting weight gain and obesity. However, this possibility has not been explored experimentally. My thesis is intended to test one such strategy in human subjects: tolerating risk to gain access to food quickly. One method of investigating our inherited food foraging strategies is to examine how we schedule our food intake, specifically intertemporal preferences to obtain food reward. My PhD used a novel task to measure individuals’ intertemporal preferences to food rewards. Participants chose between two reinforcement schedules, offering highly valued food rewards following variable or fixed delays. Overall, I found that preference for variable delay schedules was driven by the previous delivery of immediate rewards. Choice of the variable delay schedule following longer delays was enhanced following exposure to food aromas, perhaps indicating a role for food cues in tolerating prolonged delays to food rewards. By contrast, preferences for variable delay schedules were not straightforwardly related to delay discounting rates. Exploratory analyses showed only inconsistent associations with factors linked to future weight gain – body mass index (BMI), cognitive restraint, and emotional eating. However, preferences for variable delay schedules following immediate food rewards were only subtly enhanced in individuals with higher rather than lower BMIs and higher delay discounting rates. Preferences for variable delay schedules were sometimes reduced in individuals with higher restraint but increased in these individuals following exposure to food cues. This suggests that food cues might override restraint to enhance preferences for quick foods. Collectively, my findings suggest that further nvestigations of intertemporal preferences in food-scheduling behaviours might tell us about the value of quick foods in individuals vulnerable to weight gain. |
