Glycemic Index and Brain Function
Condition: Obesity
Study type: Interventional

Summary: 
      The investigators propose examine the effects of the dietary factor glycemic index (GI) on
      brain areas that control food intake and hunger. This knowledge could help design dietary
      approaches that decrease hunger, and thus promote new weight loss strategies.
    

Detailed description: 
      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.
    

Intervention name(s): Low GI; High GI
Intervention type(s): Other; Other
Intervention description(s): Subjects will be instructed to consume a liquid test meal with a low GI over 5 minutes after baseline laboratory evaluations. The low and high GI meal contain similar amounts of milk, oil, dried egg whites, equal, and vanilla extract. The low GI meal corn-starch as a carbohydrate. Both meals have similar macronutrient composition (60% carbohydrate, 15% protein, 25% fat), micronutrient profiles, physical properties, palatability and sweetness. The high vs. low GI meals have a predicted difference in GI of 90 vs. 40, and consistent with this prediction, a pilot study in obese young adults found a 2.2-fold difference in glycemic response (p<0.001). The test meals will provide 25% of individual daily energy requirements.; Subjects will be instructed to consume a liquid test meal with a high GI over 5 minutes after baseline laboratory evaluations. The low and high GI meal contain similar amounts of milk, oil, dried egg whites, equal, and vanilla extract. The high GI meal contains corn-syrup as a carbohydrate. Both meals have similar macronutrient composition (60% carbohydrate, 15% protein, 25% fat), micronutrient profiles, physical properties, palatability and sweetness. The high vs. low GI meals have a predicted difference in GI of 90 vs. 40, and consistent with this prediction, a pilot study in obese young adults found a 2.2-fold difference in glycemic response (p<0.001). The test meals will provide 25% of individual daily energy requirements.
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Primary purpose: Treatment
Keywords: Glycemic Index; Brain; Intake Regulation; Weight Loss; Hunger; Diet