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Proefschrift binnenwerk Manon Ernst_DEF.indd

C H A P T E R   1   nomic  conditions  or  a  negative  development  because  of  an  increasing  incidence  of   diseases  related  to  obesity.     Obesity  can  be  defined  as  an  overload  of  fat  mass  in  the  body.  The  degree  of  over-­‐ weight  is  determined  by  the  Body  Mass  Index  (BMI)  calculated  by  weight  (kg)  di-­‐ vided  by  the  square  height  (m2).  Adolphe  Quetelet,  a  Belgian  statistician,  introduced   the   BMI.   Therefore   the   BMI   is   also   called   the   Quetelet   index6.   The   World   Health   Organization   defines   a   BMI   between   18.5   kg/m2   and   25   kg/m2   as   healthy   while   overweight  and  obesity  are  defined  as  a  BMI  >  25  and  BMI  >  30  respectively.  One   speaks  of  morbid  obesity  in  case  of  a  BMI  >  40  kg/m2.  With  regard  to  children  the   value  of  the  BMI  is  age  dependent  and  thereby  the  cut-­‐off  point  of  abnormal  weight   may  differ  from  adults.  The  Ponderal  Index  (PI)  is  comparable  to  the  BMI,  but  the   mass   is   normalized   with   the   third   power   of   body   height   rather   than   the   second   power.  It  is  used  in  infants  because  their  body  form  is  more  cubic  instead  of  oblong.   Another   approach   is   to   depict   on   a   graph   weight   versus   height   whereby   the   two   measurements  are  used  independent  of  age.  It  makes  an  estimation  of  weight  more   reliable  in  the  case  of  extreme  tall  or  small  children.  To  date,  often-­‐used  method  is   the  measurement  of  waist  circumference  as  an  estimate  of  the  abdominal  fat  mass.   The   measurement   of   skinfolds   is   applied   to   measure   subcutaneous   fat   but   is   less   accurate  in  obese  children  because  of  the  restricted  possibility  of  verification.     It   must   be   taken   into   consideration   that   the   BMI   does   not   make   a   difference   be-­‐ tween  fat  mass  and  fat-­‐free  mass.  The  fat-­‐free  mass  represents  all  tissues  except  fat.   From  the  fat-­‐free  mass  only  the  muscle  mass  changes  in  relation  to  fat  mass  during   the   development   of   obesity.   This   difference   can   be   estimated   by   measuring   Total   Body  Water  (TBW),  the  amount  of  water  in  the  body.  TBW  is  measured  by  the  Deu-­‐ terium  dilution  method  or  doubly  labeled  water  (DLW)  method.  DLW  is  a  the  stable   isotope  of  hydrogen  and  according  to  the  Maastricht  protocol7  the  fat-­‐free  mass  can   be  calculated  by     퐶퐶!×푉푉! = 퐶퐶!×푉푉!     C1  =  concentration  of  the  label  in  the  ingested  fluid   V1  =  volume  of  the  dose   C2  =  concentration  of  the  tracer  in  the  sample   V2  =  distribution  volume  in  the  body       Due  to  the  exchange  of  the  tracer  with  non-­‐aqueous  substances  in  the  body,  V2  has   to  be  divided  by  1.04  to  determine  TBW.     To  interpret  total  body  water  in  individuals  who  differed  in  height,  the  results  are   corrected  for  height  as  TBW/height2.     12    


Proefschrift binnenwerk Manon Ernst_DEF.indd
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