Neural and Metabolic Factors in Carbohydrate Reward: An Examination of Speed

Dietary factors contributed to nearly 50% of all cardiometabolic deaths in the US in 2012, making it one of the leading causes of preventable death in the US, second only to tobacco use. Human diets and food choices can't help but be influenced by the ubiquitous availability of processed foods of high-energy density and low nutrient content, consumption of which can lead to obesity, type II diabetes, heart disease, and other types of metabolic dysfunction. Surprisingly, food reinforcement does not rely on perceived energy density. Rather food reinforcement is associated with actual energy density and therefore, on an implicit knowledge of caloric content. That implicit knowledge must have a neural signature and a mechanism by which the gut communicates nutritive value to the brain. There is evidence, at least for fat and carbohydrates, that these pathways are separable, but terminate in a common neural structure, the dorsal striatum or caudate. This could be one mechanism by which modern processed foods high in both fat and carbohydrate are so sought after and readily consumed, In fact, when experimentally tested, fat and carbohydrate combinations were more reinforcing calorie for calorie than fat or carbohydrates alone and the level of reinforcement correlated with activity in reward- related brain areas. Beyond simple reinforcing value, it is known from the literature on drugs of abuse that the faster a drug is arrives at the brain, the higher it's abuse potential, however, little is known about how the kinetics of nutrient excursion influence food preference, choice, and brain activity. This project aims to test this specifically for carbohydrate reward.