title: An obesogenic postnatal environment is more important than the fetal environment for the development of adult adiposity: a study of female twins.
abstract: BACKGROUND
  A relation between birth weight and adult body composition has been reported in singleton populations, especially when more accurate measures of body composition, such as dual-energy X-ray absorptiometry (DXA) were used. It remains uncertain whether this is mediated by a direct effect of fetal nutrition, through factors in the shared environment, or through genetic factors.
  
  
  OBJECTIVE
  The objective was to investigate the relation between birth weight and body composition with the use of a co-twin design.
  
  
  METHODS
  DXA measurements and birth weights were available for 2228 dizygotic and 842 monozygotic female twins aged between 18 and 80 y. Multivariate regression models were used to identify both individual specific relations and those mediated through the shared environment.
  
  
  RESULTS
  Significant relations were found between birth weight and DXA measures for individuals. A 1-kg increase in birth weight was associated with a 1.72-kg increase in lean mass, a 0.25-kg increase in fat mass, and a 0.05-unit increase in the lean:fat mass ratio. Within twin pairs, the analysis showed that associations between birth weight and absolute levels of lean and fat mass were mediated through individual-specific effects, whereas the relation between birth weight and the proportion of lean to fat mass was mediated purely through factors common to twin pairs.
  
  
  CONCLUSIONS
  A higher birth weight is associated with a higher proportion of lean to fat mass as adults. However, these analyses suggest that this association is not determined by individual specific factors in utero (eg, fetal nutrition) but through factors in the shared common environment of the twins.
authors: Department of Human Nutrition, University of Otago, Dunedin, New Zealand. paula.skidmore@otago.ac.nz.
authors: Paula M L
authors: PM
authors: Skidmore
authors: Aedin
authors: A
authors: Cassidy
authors: Ramasamyiyer
authors: R
authors: Swaminathan
authors: J Brent
authors: JB
authors: Richards
authors: Massimo
authors: M
authors: Mangino
authors: Tim D
authors: TD
authors: Spector
authors: Alex J
authors: AJ
authors: MacGregor
mesh_terms: D015502:Absorptiometry, Photon; D000273:Adipose Tissue / Q000378:metabolism; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001724:Birth Weight / Q000502:physiology*; D001823:Body Composition / Q000502:physiology*; D004032:Diet; D004781:Environmental Exposure; D005260:Female; D006801:Humans; D008875:Middle Aged; D015999:Multivariate Analysis; D018482:Muscle, Skeletal / Q000378:metabolism; D009765:Obesity / Q000453:epidemiology* / Q000209:etiology / Q000235:genetics; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects; D039401:Prenatal Nutritional Physiological Phenomena / Q000502:physiology*; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic; D006113:United Kingdom; D055815:Young Adult