Ultra-Processed Foods, Palatability, Appetite, and Gastrointestinal Transit

This is a randomized crossover trial examining the effects of food processing level and palatability on appetite and gastrointestinal transit time. Participants will complete a screening visit followed by four test visits, with each test visit separated by at least one week. Each participant will consume all four test meals: high-palatability ultra-processed food, low-palatability ultra-processed food, high-palatability non-ultra-processed food, and low-palatability non-ultra-processed food. Palatability will be reduced by adding bitter melon powder to the low-palatability meals. During each test visit, participants will consume the assigned test meal containing lactulose as a marker of gastrointestinal transit time. Breath samples will be collected to assess orocecal transit time using hydrogen analysis. Participants will also rate meal palatability and appetite sensations, including hunger, fullness, desire to eat, amount they could eat, and thirst, using visual analog scales during the test visit.