title: Physical activity and fat mass gain in Mexican school-age children: a cohort study.
abstract: BACKGROUND
  In México, the prevalence of unhealthy weight increased from 24% at 6 y to 33% at 12 y of age, opening a window of opportunity to better understand the pathogenesis of obesity. The objective of this study was to explore the association between time spent on medium, vigorous physical activity (MVPA) and concurrent gains in BMI, fat mass (FM) and fat-free mass (FFM), alternately, in a cohort of Mexican children followed from kindergarten (baseline) to 2nd grade elementary school (endline).
  
  
  METHODS
  The MVPA (5-d accelerometry), BMI, FM and FFM (air displacement plethysmography) were measured at baseline and endline. Associations between gains in BMI, FM and FFM and changes in MVPA were examined using lagged and dynamic regression models, controlling for energy intake and demographic variables.
  
  
  RESULTS
  A total of 205 children were analyzed. Gender affected the effect of MVPA on FM gain. In girls, a high baseline MVPA predicted a lower FM gain (-0.96 kg, p=0.025) compared to low/medium MVPA. Increasing, decreasing or having a persistently high MVPA predicted a lower FM gain (range -1.6 to -1.03 kg, p<0.05) compared to persistently low MVPA. In boys, increases in MVPA were associated with higher gains in BMI (+0.76 kg/m2, p=0.04) and FFM (+1.1 kg, p=0.01) compared to persistently low MVPA.
  
  
  CONCLUSIONS
  These results support a protective role of MVPA on FM gain in girls, suggesting that it may play a crucial role in the development of obesity. Further research on the gender effect of MVPA is warranted to better understand its role in the prevention and control of overweight and obesity.
authors: Division of Nutrition and Health, National Institute of Public Health of Mexico, Av Universidad 655 Col Sta Ma Ahuacatitlán, Cuernavaca, Morelos C.P. 62100, Mexico.
authors: Alejandra
authors: A
authors: Jáuregui
authors: Salvador
authors: S
authors: Villalpando
authors: Eduardo
authors: E
authors: Rangel-Baltazar
authors: Yaveth A
authors: YA
authors: Lara-Zamudio
authors: Marcia M
authors: MM
authors: Castillo-García
mesh_terms: D050154:Adiposity; D015992:Body Mass Index; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D015444:Exercise; D005260:Female; D006801:Humans; D016014:Linear Models; D008137:Longitudinal Studies; D008297:Male; D008800:Mexico; D009765:Obesity / Q000209:etiology*; D011446:Prospective Studies; D012737:Sex Factors; D015430:Weight Gain