Glycemic Index - Variability Among Individuals
Condition: Diabetes; Obesity; Metabolic Syndrome; Cardiovascular Disease
MeSH terms: Cardiovascular Diseases; Metabolic Syndrome
Study type: Interventional

Summary: 
      The purpose of this study is to determine the variability in glycemic index determinations
      for individual foods and food combinations. The study will also evaluate the changes in
      insulin and free fatty acid levels, plasma lipid and lipoprotein profiles, C-reactive
      protein-a marker of inflammation and glycosylated hemoglobin- a marker of glucose metabolism
      during a five-hour period after eating the food or foods. Additionally, supplementary data on
      variation in oral sensation, habitual food intake, food preferences and genes mediating
      sensory perception and dietary behaviors (supported by a grant from the Tufts Ross Aging
      Initiative) will be related to the outcomes on the present study.
    

Detailed description: 
      The objective of this proposal is to investigate the intra-individual reproducibility (within
      the same individual, when repeatedly measured) and inter-individual variability (among
      individuals) of glycemic index (GI) and glycemic load (GL) value determinations for
      individual foods and food combinations. The specific aims to accomplished this objective are
      to evaluate reproducibility and variability of GI value determinations in volunteers
      differing in biologic characteristics - body mass index (BMI), age and gender; assess the
      effect of macronutrient amounts and combinations, and fiber on variability of GI and GL value
      determinations; assess the effect of prior meal macronutrient composition ('second meal'
      effect) on GI value determinations; and relate these data to chronic disease risk factors
      monitored prior to and during the intervention period. These aims will be accomplished by
      assessing intra-individual reproducibility and inter-individual variability of repeated GI
      value determinations for white bread, commonly used as a reference food, relative to glucose,
      in volunteers selected to represent a range of BMI's (18-24.9, 25-29.9, 30-35) and ages
      (18-49.9, 50-85 y), and on the basis of gender, and relate these data to body composition and
      insulin sensitivity (Phase I). This work will then be extended to address issues related to
      variability potentially introduced by differences in macronutrient and fiber combinations and
      loads (Phase II), and finally by 'second meal' effects (Phase III). Prior to each set of food
      challenges (glucose and test food[s] in random order) volunteers will be characterized on the
      basis of fasting HbA1c; lipids and lipoproteins; insulin, glucose and C-reactive protein.
      During the 5-hour challenge (sampling at 0, 15, 30, 45, 60, and every 30 minutes thereafter)
      volunteers will be monitored for changes in blood glucose, insulin, triglycerides, total, low
      density lipoprotein and high density lipoprotein cholesterol, and non-esterified fatty acid
      levels. Additionally, supplementary data on variation in oral sensation, habitual food
      intake, food preferences and genes mediating sensory perception and dietary behaviors
      (supported by a grant from the Tufts Ross Aging Initiative) will be related to the outcomes
      on the present study. The concepts of both GI and GL are in the public domain and it has been
      suggested that the concepts be incorporated into U.S. federal dietary guidance (U.S. Dietary
      Guidelines and Dietary References Intakes) formulated to promote health and reduce chronic
      disease risk. This proposal addresses some of the understudied areas for which additional
      information would be useful in order to determine whether GI and GL should be used to
      classify foods on an individual basis, as has been suggested, and when formulating dietary
      guidance for the general population.
    

Intervention name(s): Carbohydrate + Protein; Carbohydrate + Fat; Fiber; Carbohydrate load
Intervention type(s): Other; Other; Other; Other
Intervention description(s): Light Tuna Packed in water.; Butter; Unrefined Carbohydrate; Carbohydrate
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Double (Investigator, Outcomes Assessor)
Primary purpose: Basic Science
Keywords: Glycemic Index; Glycemic Load; Glucose; Insulin; Lipoproteins; Free fatty acids