Food choice and preference have been linked to post-ingestive consequences of food consumption. Many ultra-processed foods deliver calories rapidly and are highly rewarding. In literature surrounding substances of abuse, the speed at which a drug reaches the brain affects its abuse potential; this is known as the "rate hypothesis." Here, we test whether the rate hypothesis of addiction may apply to food, specifically whether caloric availability, or the speed at which carbohydrate becomes available for use, contributes to food reward and preference. To do this, we use beverages with novel flavors (conditioned stimulus (CS)) mixed with either a slow metabolizing carbohydrate (maltodextrin and inulin; CS+Slow), a fast-metabolizing carbohydrate (sucrose; CS+Fast), or no carbohydrate (sucralose; CS-). Participants are given each of these drinks 6 times to consume (conditioning period). 2 of these consumption periods occur during in-lab sessions. In one session, blood glucose is measured over one hour post-consumption. In another, we perform indirect calorimetry to assess post-consumption changes in substrate oxidation rates. At the post-testing session, changes in self-reported liking, wanting, and ad libitum intake of each beverage are recorded. Brain response to each flavor cue (without calories) is measured using fMRI at the post-test. We hypothesize the flavor paired with the CS+Fast will be the most liked, wanted, and consumed. We expect greater BOLD (blood oxygenated level dependent) activation to the CS+Fast relative to the CS+Slow and CS- in the nucleus accumbens and hypothalamus. This is an ongoing study and, here, we present our preliminary analysis of the data. / Doctor of Philosophy / People make food choices every day throughout their lives, but why? Research in the past has shown that there are aspects of an individual's life that may be affecting their preferences for foods. One of the aspects investigated in this analysis is metabolism. The way and speed that the body uses carbohydrates plays a large role in how an individual views food options. Here, we test if the speed at which the body is able to use carbohydrates affects their choices of food and if there are any neural components to these food options. To do this, we tested multiple carbohydrates to determine which were the best for comparisons of slow- and fast-metabolizing. These carbohydrate groups were tested against a drink containing no carbohydrates in two metabolic measurements: blood glucose and energy expenditure. We then used a magnetic resonance imaging scan to test brain activity when participants are given small amounts of each drink without carbohydrates. Each carbohydrate condition was paired with a novel flavor so participants wouldn't have a preconceived idea about the caloric load. We found drinks with sucrose, a common household sugar, had the fastest change in metabolic measures. Additionally, areas in the brain related to rewards and learning were activated by flavors associated with sucrose. This leads us to believe that carbohydrates that are quickly used by your body are more rewarding in the brain and may have implications for preferences down the line.