The Chocolate Study
Condition: Obesity
MeSH terms: Obesity
Study type: Observational

Summary: 
      The purpose of this study is to test the dynamic vulnerability model of obesity using brain
      imaging.
    

Detailed description: 
      Obese vs lean humans show greater gustatory/oral somatosensory and reward region responsivity
      to palatable food images/cues and this predicts future weight gain (Yokum et al., 2011; Stice
      et al., 2008, 2010b; Stoeckel et al., 2008), in line with reward surfeit and incentive
      sensitization models of obesity (Berridge, 2009; Davis et al., 2004). Yet, obese vs lean
      humans have fewer dopamine (DA) receptors in striatal reward regions, show reduced striatal
      response to palatable food intake, and low striatal response predicts future weight gain in
      those at genetic risk for reduced DA signaling (Felsted et al., 2010; Stice et al., 2008;
      Wang et al., 2001; Volkow et al., 2008), in line with the reward deficit model of obesity
      (Wang et al., 2002b). One explanation for the mixed findings is that some of these findings
      reflect initial risk factors and others result from overeating. Firing of DA neurons in
      reward regions shifts from food intake to cues that predict food intake after conditioning
      (Kiyatkin et al., 1994; Schultz et al., 1993) and overeating leads to reduced D2 receptor
      density, D2 sensitivity, and reward sensitivity in rats (Alsio et al., 2010; Kelley et al.,
      2003; Johnson & Kenny, 2010) and striatal response to food in humans (Stice et al., 2010a),
      implying that overeating leads to increased incentive sensitization and down-regulation of
      reward regions. Further, reduced inhibitory region response to food images/cues predicts
      future overeating and weight gain (Cornier et al., 2010). Data imply that youth at risk for
      obesity initially show greater responsivity of regions that encode the reward value of food
      cues, coupled with greater responsivity of gustatory/oral somatosensory regions that encode
      the sugar and fat content of foods, and with reduced inhibitory region responsivity, which
      lead to overeating/weight gain that produces blunted striatal DA signaling, increased
      responsivity of reward valuation regions to food cues, and reduced inhibitory activation in
      response to food stimuli, increasing risk for further overeating/weight gain. We propose to
      conduct a rigorous test of this dynamic-vulnerability model using a novel repeated measures
      fMRI design in which teens complete scans annually over 4 years. Aim 1: test whether elevated
      gustatory/oral somatosensory and reward region responsivity and reduced inhibitory region
      responsivity to palatable food images, cues, and intake of food varying in sugar/fat content,
      and behavioral inhibitory control deficits/immediate reward bias predict initial increases in
      % body fat in 130 lean teens. Aim 2: use growth curve models to test whether initial
      increases in % body fat and energy dense food intake predict future decreases in striatal
      response to palatable food receipt, increases in reward circuitry response to palatable food
      images/cues, decreased inhibitory region response to food images/cues, and increased
      behavioral inhibitory control deficits/immediate reward bias. Aim 3: test whether decreased
      striatal response to palatable food, increased reward region response to food images/cues,
      reduced inhibitory region response to food images/cues, behavioral inhibitory control
      deficits/immediate reward bias predict further escalation in % body fat.
    

Intervention name(s): Functional Magnetic Resonance Imaging
Intervention type(s): Other
Observational model: Cohort
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        130 lean adolescents between 14-16 years old with BMIs between the 25th and 75th percentile
        at baseline