Glycemic Index and Brain Function

Most individuals have great difficulty following reduced calorie diets because they
experience increased hunger. This process is regulated by specific brain areas. Though many
psychological and environmental factors are involved, physiological effects of diet may have
a significant impact. The postprandial rise in blood glucose, quantified by the glycemic
index (GI), is of particular interest. High GI meals elicit hormonal events that limit
availability of metabolic fuels, causing hunger and overeating, especially in people with
high insulin secretion.

Our aim is to examine how postprandial changes after high versus low GI meals affect hunger
and brain function in areas of intake control. Specifically, we speculate that obese
individuals will demonstrate functional changes in brain areas of intake control and
increased hunger after a high versus low GI meal.

We will recruit obese, young adults and quantify their insulin secretion during a 2-hour
oral glucose tolerance test. A brief practice MRI session will serve to familiarize the
subjects with the scanning process. During the two test sessions, standardized test meals
with high versus low GI will be given in a randomized, blinded cross-over design. Serial
blood levels of hormones, metabolic fuels, and metabolites will be correlated with perceived
hunger, and a perfusion MRI scan will be performed to assess brain activation during the
late postprandial phase, at the nadir of blood sugar and insulin levels (4 hours
postprandial).

This work will inform an integrated physiological model relating peripheral postprandial
changes to brain function and hunger. In addition, findings may provide evidence of a novel
diet-phenotype, in which baseline clinical characteristics can be used to predict which
weight loss diet will work best for a specific individual. Metabolite profiling might shed
light on the mechanisms linking diet composition to brain function, and provide feasible
clinical markers of the identified phenotype to facilitate translation into practice.