title: Validity of air-displacement plethysmography in the assessment of body composition changes in a 16-month weight loss program.
abstract: OBJECTIVE
  To compare the accuracy of air displacement plethysmography (ADP) and dual energy x-ray absorptionmetry (DXA) in tracking changes in body composition after a 16 month weight loss intervention in overweight and obese females.
  
  
  METHODS
  93 healthy female subjects (38.9 +/- 5.7 yr, 159.8 +/- 5.6 cm, 76.7 +/- 9.9 kg, 30.0 +/- 3.4 kg/m2) completed a 16 month weight loss intervention. Eligible subjects attended 15 treatment sessions occurring over the course of 4 months with educational content including topics relating to physical activity and exercise, diet and eating behavior, and behavior modification. In the remaining 12 months, subjects underwent a lifestyle program designed to increase physical activity and improve eating habits. Before and after the intervention, subjects had their percent body fat (%fat), fat mass (FM), and fat-free mass (FFM)) assessed by DXA and ADP.
  
  
  RESULTS
  Significant differences (p < or = 0.001) were found between DXA and ADP at baseline %fat (46.0 % fat vs. 42.0 % fat), FM (35.3 kg vs. 32.5 kg) and FFM (40.8 kg vs. 44.2 kg) as well as at post intervention for %fat (42.1% fat vs. 38.3 % fat), FM (30.9 kg vs. 28.4 kg) and FFM (41.7 kg vs. 44.7 kg). At each time point, ADP %fat and total FM was significantly lower (p < or = 0.001) than DXA while FFM was significantly higher (p < or = 0.001). However, both techniques tracked %fat changes similarly considering that there were no differences between the two means. Furthermore, a Bland-Altman analysis was performed and no significant bias was observed, thus demonstrating the ability of ADP to measure body fat across a wide range of fatness.
  
  
  CONCLUSIONS
  At baseline and post weight loss, a significant difference was found between ADP and DXA. However, the results indicate both methods are highly related and track changes in %fat similarly after a weight loss program in overweight and obese females. Additionally, the mean changes in %fat were similar between the two techniques, suggesting that ADP can be translated to its use in clinical practice and research studies as DXA currently is used.
authors.affiliation: Exercise and Health Laboratory, Faculty of Human Movement, Health and Exercise Science, Technical University of Lisbon, Portugal. claudiam@fmh.utl.pt
authors.forename: Cláudia S
authors.initials: CS
authors.lastname: Minderico
authors.forename: Analiza M
authors.initials: AM
authors.lastname: Silva
authors.forename: Pedro J
authors.initials: PJ
authors.lastname: Teixeira
authors.forename: Luis B
authors.initials: LB
authors.lastname: Sardinha
authors.forename: Holly R
authors.initials: HR
authors.lastname: Hull
authors.forename: David A
authors.initials: DA
authors.lastname: Fields