Validity of DXA body volume equations in a four-compartment model for adults with varying body mass index and waist circumference classifications.

The purpose of this investigation was to determine the validity of 4-compartment (4C) model body fat percent (BF%) estimates when using dual energy x-ray absorptiometry (DXA) derived body volume (BV) equations (4C-DXA1 and 4C-DXA2) in adults with varying body mass index (BMI) and waist circumference (WC) classifications. Each model was compared to a criterion 4C model with air-displacement plethysmography (ADP) generated BV (4C-ADP). Participants were categorized as normal weight (n = 40; NW = BMI<25.0kg/m2); overweight (n = 40; OWBMI = BMI≥25.0 kg/m2); and overweight with at-risk WC (n = 35; OWBMI+WC = BMI≥25.0 kg/m2 and WC≥88.0cm for women and 102.0cm for men). 4C-DXA1 produced lower BF% than that derived using the 4C-ADP in NW (CE = -3.0%; p<0.001) while 4C-DXA2 was significantly higher (CE = 4.8%; p<0.001). The SEE and 95% limits of agreement (LOA) were lower for 4C-DXA2 (1.24% and ±2.5%, respectively) than 4C-DXA1 (2.59% and ±5.0%, respectively) and proportional bias was present for both (p<0.05). 4C-DXA1 BF% was not significant in OWBMI (CE = -0.5%; p = 0.112) whereas 4C-DXA2 was higher (CE = 4.5%; p<0.001). The SEE and 95% LOA were lower for 4C-DXA2 (1.20% and ±2.9%, respectively) than 4C-DXA1 (1.92% and ±3.9%, respectively) in OWBMI. Proportional bias was present for 4C-DXA1 (p = 0.007), but not 4C-DXA2 (p = 0.832). 4C-DXA1 and 4C-DXA2 produced significantly higher BF% in OWBMI+WC (CE = 2.2 and 2.3%, respectively; both p<0.001). The SEE and 95% LOA remained lower for 4C-DXA2 (1.15% and ±2.5%, respectively) than 4C-DXA1 (1.84% and ±3.8%, respectively). There was proportional bias for 4C-DXA2 (p = 0.020), but not 4C-DXA1 (p = 0.183) in OWBMI+WC. Only one prediction model (i.e., 4C-DXA1 in OWBMI+WC) revealed valid estimates of BF%. Practitioners are encouraged to use criteria for both BMI and WC when utilizing DXA-derived BV in 4C-models for normal and overweight populations.

An Investigation of the Differences between Perceived vs. Measured Body Composition, Social Physique Anxiety, and Overall Appearance Satisfaction among College Students.

The purpose of this study was to examine the differences between body composition, social physique anxiety (SPA) and appearance satisfaction among college students by sex and BMI. A secondary purpose was to assess levels of appearance satisfaction before and after body composition testing and discover any differences between perceived body fat percentage (BF%) and weight versus actual measurements. Participants included 212 college students (93 males, 119 females), 22.0 ± 2.2 years. They answered a demographic questionnaire, the Social Physique Anxiety Scale (SPAS), post-assessment questions, and underwent body composition testing via dual energy x-ray absorptiometry (DXA). There was a significant correlation between measured BF% and SPAS scores (r = 0.531, P < 0.001). Males scored lower on the SPAS compared to females (25.3 ± 9.4 vs. 33.1 ± 9.1, P < 0.001). The sample underestimated BF% with females underestimating by more than males, 5.7 ± 7.3% vs. 3.7 ± 5.4%, P = 0.036. There was no difference between perceived and measured weight for women (P = 0.500) however, males overestimated their weight (P = 0.004). There was a difference in appearance satisfaction pre and post body composition for females (pre = 4.4 ± 1.7, post = 4.2 ± 1.9, P = 0.026) but not for males (pre = 5.3 ± 1.5, post = 5.0 ± 1.8, P = 0.063). Overall, males had lower levels of SPA and higher levels of appearance satisfaction than females and knowledge of BF% negatively affected appearance satisfaction scores for females. Finally, both males and females underestimated BF% compared to DXA.

A Comparison of Body Composition Across Two Phases of the Menstrual Cycle Utilizing Dual-Energy X-Ray Absorptiometry, Air Displacement Plethysmography, and Bioelectrical Impedance Analysis.

The purpose of this investigation was to utilize several different technologies to compare body composition results across two phases of the menstrual cycle, and to investigate whether being on hormonal birth control or not has any effect on results. The secondary purpose was to determine if body satisfaction or perception of fluid retention differed across phases or between groups. A total of 39 females with a mean age of 26 ± 7 yrs were included in the study, 15 were on hormonal birth control (BC) and 24 were not (non-BC). Participants came into the lab for two trials: once while menstruating and another during the estimated pre-ovulation phase of the menstrual cycle. Demographic and body satisfaction questionnaires were completed prior to body composition testing. This testing included dual-energy x-ray absorptiometry, BOD POD®, and three separate bioelectrical impedance analyses. Participants completed the body satisfaction questionnaire and all body composition tests on each trial. No significant differences (P > 0.05) were found between body fat percentage or total body water estimates taken during menses and pre-ovulation for the BC or non-BC group. There was no significant difference (P > 0.05) in overall body satisfaction across the two phases for the non-BC group, though the BC group had significantly lower body satisfaction during menses (P < 0.01). Participants in both groups identified feeling more bloated during menses (P < 0.001). Results suggest that menses should not affect the reliability of body composition estimates regardless of whether or not females are on hormonal BC.