title: Why doesn't the brain lose weight, when obese people diet?
abstract: OBJECTIVE
  As has been shown recently, obesity is associated with brain volume deficits. We here used an interventional study design to investigate whether the brain shrinks after caloric restriction in obesity. To elucidate mechanisms of neuroprotection we assessed brain-pull competence, i.e. the brain's ability to properly demand energy from the body.
  
  
  METHODS
  In 52 normal-weight and 42 obese women (before and after ≈10% weight loss) organ masses of brain, liver and kidneys (magnetic resonance imaging), fat (air displacement plethysmography) and muscle mass (dual-energy X-ray absorptiometry) were assessed. Body metabolism was measured by indirect calorimetry. To investigate how energy is allocated between brain and body, we used reference data obtained in the field of comparative biology. We calculated the distance between each woman and a reference mammal of comparable size in a brain-body plot and named the distance 'encephalic measure'. To elucidate how the brain protects its mass, we measured fasting insulin, since 'cerebral insulin suppression' has been shown to function as a brain-pull mechanism.
  
  
  RESULTS
  Brain mass was equal in normal-weight and obese women (1,441.8 ± 14.6 vs. 1,479.2 ± 12.8 g; n.s.) and was unaffected by weight loss (1,483.8 ± 12.7 g; n.s.). In contrast, masses of muscle, fat, liver and kidneys decreased by 3-18% after weight loss (all p < 0.05). The encephalic measure was lower in obese than normal-weight women (5.8 ± 0.1 vs. 7.4 ± 0.1; p < 0.001). Weight loss increased the encephalic measure to 6.3 ± 0.1 (p < 0.001). Insulin concentrations were inversely related to the encephalic measure (r = -0.382; p < 0.001).
  
  
  CONCLUSIONS
  Brain mass is normal in obese women and is protected during caloric restriction. Our data suggest that neuroprotection during caloric restriction is mediated by a competent brain-pull exerting cerebral insulin suppression.
authors.affiliation: Medical Clinic I, University of Lübeck, Lübeck, Germany. achim.peters@uk-sh.de
authors.forename: Achim
authors.initials: A
authors.lastname: Peters
authors.forename: Anja
authors.initials: A
authors.lastname: Bosy-Westphal
authors.forename: Britta
authors.initials: B
authors.lastname: Kubera
authors.forename: Dirk
authors.initials: D
authors.lastname: Langemann
authors.forename: Kristin
authors.initials: K
authors.lastname: Goele
authors.forename: Wiebke
authors.initials: W
authors.lastname: Later
authors.forename: Martin
authors.initials: M
authors.lastname: Heller
authors.forename: Christian
authors.initials: C
authors.lastname: Hubold
authors.forename: Manfred James
authors.initials: MJ
authors.lastname: Müller
mesh_terms: D000273:Adipose Tissue / Q000033:anatomy & histology; D000328:Adult; D000818:Animals; D001921:Brain / Q000033:anatomy & histology* / Q000378:metabolism; D031204:Caloric Restriction; D002153:Calorimetry, Indirect; D016022:Case-Control Studies; D004038:Diet, Reducing; D004734:Energy Metabolism; D005260:Female; D006801:Humans; D007328:Insulin / Q000097:blood*; D007668:Kidney / Q000033:anatomy & histology; D008099:Liver / Q000033:anatomy & histology; D018482:Muscle, Skeletal / Q000033:anatomy & histology; D009765:Obesity / Q000378:metabolism*; D009929:Organ Size; D012016:Reference Values; D015431:Weight Loss / Q000502:physiology*
chemical_list: D007328:Insulin