David A. Fields

Total body fat does not influence maximal aerobic capacity

OBJECTIVE: The objective of this study was to examine the influence of body weight and body composition on aspects of aerobic fitness. Our hypothesis was that increased body weight, specifically increased fat mass (FM), would not limit VO2max relative to fat-free mass (FFM), but would reduce maximal and sub-maximal VO2max relative to body weight.DESIGN: We used data from two ongoing studies. In Study 1 a cross-sectional analysis of 129 children across a wide spectrum of body composition was performed. In Study 2 we examined data from 31 overweight women before and after weight loss.METHODS: VO2max was measured using a treadmill test. Sub-maximal aerobic capacity was evaluated with respiratory exchange ratio (RER), heart-rate (HR), and oxygen uptake relative to VO2max at a given workload (%VO2max). Body composition was assessed using dual energy X-ray absorptiometry (DXA) (Study 1) and a four-compartment model (Study 2).RESULTS: In Study 1, FFM was the strongest determinant of VO2max (r=0.87; P<0.0001). After adjusting for FFM, there was no significant influence of FM on VO2max. After separating children into lean and obese sub-groups, absolute VO2max was significantly higher in the obese (1.24±0.27 vs 1.56±0.40) and VO2max relative to body weight was significantly lower (44.2±3.2 vs 32.0±4.1 ml/(kg-min)), whereas there was no significant difference when expressed relative to FFM (57.9±5.8 vs 59.2±4.9 ml/(kgFFM-min)). Sub-maximal aerobic capacity was significantly lower in the obese children, as indicated by a higher HR and %VO2max; time to exhaustion was significantly lower in the obese children (15.3±2.9 vs 11.1±2.1 min). In Study 2, FFM was also the strongest determinant of VO2max before and after weight loss. The relationship between VO2max and FFM was identical before and after weight loss so that VO2max relative to FFM was identical before and after weight loss (43.8±4.9 vs 45.5±6.4 ml/(kgFFM-min)). However, sub-maximal aerobic capacity was lower in the obese state, as indicated by a significantly higher RER (0.85±0.06 vs 0.79±0.05), HR (124±14 vs 102±11 bpm), and %VO2max (44% vs 36%).CONCLUSION: The major influence of body weight on VO2max is explained by FFM; FM does not have any effect on VO2max. Fatness and excess body weight do not necessarily imply a reduced ability to maximally consume oxygen, but excess fatness does have a detrimental effect on submaximal aerobic capacity. Thus, fatness and VO2max should be considered independent entities.

Aerobic Fitness, Not Energy Expenditure, Influences Subsequent Increase in Adiposity in Black and White Children

Background. Low levels of energy expenditure and aerobic fitness have been hypothesized to be risk factors for obesity. Longitudinal studies to determine whether energy expenditure influences weight gain in whites have provided conflicting results. To date, no studies have examined this relationship in blacks or whether aerobic fitness influences weight gain in white or black children. Methods. One hundred fifteen children, 72 white (55 girls and 17 boys) and 43 black (24 girls and 19 boys) were recruited for this study. Aerobic fitness, resting, total, and activity-related energy expenditure and body composition were measured at baseline. The children returned annually for 3 to 5 repeated measures of body composition. The influence of the initial measures of energy expenditure and fitness on the subsequent rate of increase in adiposity was examined, adjusting for initial body composition, age, ethnicity, gender, and Tanner stage. Because 20 children did not attain maximum oxygen consumption, the sample size for the combined analysis was 95. Results. Initial fat mass was the main predictor of increasing adiposity in this cohort of children, with greater initial fat predicting a higher rate of increase of adiposity. There was also a significant negative relationship between aerobic fitness and the rate of increasing adiposity (F 1,82 = 3.92). With every increase of .1 L/minute of fitness, there was a decrease of .081 kg fat per kg of lean mass gained. None of the measures of energy expenditure significantly predicted increasing adiposity in white or black children. Conclusions. Initial fat mass was the dominant factor influencing increasing adiposity; however, aerobic fitness was also a significant independent predictor of increasing adiposity in this cohort of children. Resting, total, or activity-related energy expenditure did not predict increasing adiposity. It seems that aerobic fitness may be more important than absolute energy expenditure in the development of obesity in white or black children. energy expenditure, fitness, longitudinal, obesity.

Impact of maternal body mass index on neonate birthweight and body composition

OBJECTIVE The purpose of this study was to compare bodyweight and composition (percent fat, fat mass, and fat-free mass) in neonates born to mothers with a normal pregravid body mass index (BMI; < 25 kg/m(2)) vs neonates born to mothers with an overweight/obese pregravid BMI (> or = 25 kg/m(2)). STUDY DESIGN Seventy-two neonates (33 from normal mothers and 39 from overweight/obese mothers) of singleton pregnancies with normal glucose tolerance had their bodyweight and body composition assessed by air-displacement plethysmography. RESULTS After controlling for neonate age at time of testing, significant differences were found between groups for percent fat (12.5 +/- 4.2% vs 13.6 +/- 4.3%; P < or = .0001), fat mass (414.1 +/- 264.2 vs 448.3 +/- 262.2 g; P < or = .05), and fat-free mass (3310.5 +/- 344.6 vs 3162.2 +/- 343.4 g; P < or = .05), with no significant differences between birth length (50.7 +/- 2.6 vs 49.6 +/- 2.6 cm; P = .08) or birthweight (3433.0 +/- 396.3 vs 3368.0 +/- 399.6 g; P = .44). CONCLUSION Neonates born to mothers who have a normal BMI have significantly less total and relative fat and more fat-free mass than neonates born to overweight/obese mothers. Although preliminary, these data suggest that the antecedents of future disease risk (eg, cardiovascular disease, diabetes, and obesity) occur early in life.

Validation of the BOD POD with hydrostatic weighing: influence of body clothing.

OBJECTIVE: Whole body air-displacement plethysmography (BOD POD), a new body composition technique, was validated against hydrodensitometry (UWW) in 67 women wearing a one-piece swimsuit (OP) who represent a wide range of body fatness and age. Additionally, the effect of trapped isothermic air in clothing while in the BOD POD was examined by comparing different clothing schemes (a one-piece swimsuit (OP), two-piece swimsuit (TP), a hospital gown (HG), and a hospital gown previously included in a volume calibration (GC)) in a subset of 25 women.DESIGN: Cross-sectional data analysis.SUBJECTS: 67 healthy Caucasian females.MEASUREMENTS: Body density g/cm3 (Db) by BOD POD and UWW.RESULTS: In 67 females UWW Db (1.030±0.020 g/cm3) was higher (P<0.01) than BOD POD Db (1.028±0.020 g/cm3). This is a difference of 1.0% fat. The R2 was 0.94, SEE was 0.005 g/cm3 and the regression between Db by UWW and BOD POB did not significantly deviate from the line of identity. In the subset group of 25 subjects, OP Db (1.040±0.014 g/cm3) and TP Db (1.040±0.014 g/cm3) were significantly lower (P<0.01) than UWW Db (1.044±0.014 g/cm3) or a difference of 1.9% fat. The R2 was 0.86 and the SEE was 0.005 g/cm3 and the regression between Db by UWW and both OP and TP did not significantly deviate from the line of identity. HG Db (1.056±0.016 g/cm3) and GC Db (1.037±0.016 g/cm3) were significantly different (P<0.01) from UWW Db (1.044±0.014 g/cm3). This difference in density translates to a difference of 5.5% and 3.2% fat respectively. The regression between Db by UWW and both HG and GC significantly deviated from the line of identity.CONCLUSION: This study supports the use of the BOD POD as a substitute for UWW. However, caution should be made in using the BOD POD if subjects are clothed in anything other than a tight fitting swimsuit.

Relationship of insulin, glucose, leptin, IL-6 and TNF-α in human breast milk with infant growth and body composition.

Numerous appetite, growth, obesity‐related hormones and inflammatory factors are found in human breast‐milk, but there is little evidence on their relationship with infant body composition.

Freshman 15: Fact or fiction?

Objective: The objective of this study was to investigate changes in body weight, BMI, body composition, and fat distribution among freshman women during their 1st year of college.

Comparison of the BOD POD with the four-compartment model in adult females.

PURPOSE This study was designed to compare the accuracy and bias in estimates of total body density (Db) by hydrostatic weighing (HW) and the BOD POD, and percent body fat (%fat) by the BOD POD with the four-compartment model (4C model) in 42 adult females. Furthermore, the role of the aqueous and mineral fractions in the estimation of body fat by the BOD POD was examined. METHODS Total body water was determined by isotope dilution ((2)H(2)0) and bone mineral was determined by dual-energy x-ray absorptiometry. Db and %fat were determined by the BOD POD and HW. The 4C model of Baumgartner was used as the criterion measure of body fat. RESULTS HW Db (1.0352 g x cm(-3)) was not statistically different (P = 0.35) from BOD POD Db (1.0349 g x cm(-3)). The regression between Db by HW and the BOD POD significantly deviated from the line of identity (Db by HW = 0.90 x Db by BOD POD + 0.099; R(2) = 0.94). BOD POD %fat (28.8%) was significantly lower (P < 0.01) than %fat by the 4C model (30.6%). The regression between %fat by the 4C model and the BOD POD significantly deviated from the line of identity (%fat by 4C model = 0.88 x %fat by BOD POD + 5.41%; R(2) = 0.92). BOD POD Db and %fat showed no bias across the range of fatness. Only the aqueous fraction of the fat-free mass (FFM) had a significant correlation with the difference in %fat between the 4C model and the BOD POD. CONCLUSION These data indicate that the BOD POD underpredicted body fat as compared with the 4C model, and the aqueous fraction of the FFM had a significant effect on estimates of %fat by the BOD POD.

Air-displacement plethysmography: here to stay.

Purpose of reviewAir-displacement plethysmography holds promise as an alternative to more traditional body composition techniques, although our understanding of air-displacement plethysmography is less than complete. Specifically, factors that influence its validity and application in certain populations, for example children, the obese, and athletes, must be better understood. This review will summarize recent findings on the validity and precision of air-displacement plethysmography and will focus primarily on papers published since 2004, with particular attention on its use in infants. Recent findingsThe most significant recent findings in the air-displacement plethysmography literature are mechanistic in nature specifically dealing with measurement issues such as heat, moisture, clothing, and recently, inter-device variability. SummaryIt is important to recognize that air-displacement plethysmography can be a practical instrument in the evaluation of body composition in a wide range of populations. Therefore, based on the body of literature that has emerged, air-displacement plethysmography appears to be a suitable and reliable instrument in the assessment of body composition. Of particular interest is its use in pediatric and obese individuals, areas requiring further study. Research is also needed to help us better understand sources of measurement error.

Weighing the Evidence of Common Beliefs in Obesity Research

Obesity is a topic on which many views are strongly held in the absence of scientific evidence to support those views, and some views are strongly held despite evidence to contradict those views. We refer to the former as “presumptions” and the latter as “myths.” Here, we present nine myths and 10 presumptions surrounding the effects of rapid weight loss; setting realistic goals in weight loss therapy; stage of change or readiness to lose weight; physical education classes; breastfeeding; daily self-weighing; genetic contribution to obesity; the “Freshman 15”; food deserts; regularly eating (versus skipping) breakfast; eating close to bedtime; eating more fruits and vegetables; weight cycling (i.e., yo-yo dieting); snacking; built environment; reducing screen time in childhood obesity; portion size; participation in family mealtime; and drinking water as a means of weight loss. For each of these, we describe the belief and present evidence that the belief is widely held or stated, reasons to support the conjecture that the belief might be true, evidence to directly support or refute the belief, and findings from randomized controlled trials, if available. We conclude with a discussion of the implications of these determinations, conjecture on why so many myths and presumptions exist, and suggestions for limiting the spread of these and other unsubstantiated beliefs about the obesity domain.

Assessment of body composition by air-displacement plethysmography: influence of body temperature and moisture

BackgroundTo investigate the effect of body temperature and moisture on body fat (%fat), volume and density by air-displacement plethysmography (BOD POD).Methods%fat, body volume and density by the BOD POD before (BOD PODBH) and immediately following hydrostatic weighing (BOD PODFH) were performed in 32 healthy females (age (yr) 33 ± 11, weight (kg) 64 ± 14, height (cm) 167 ± 7). Body temperature and moisture were measured prior to BOD PODBH and prior to BOD PODFH with body moisture defined as the difference in body weight (kg) between the BOD PODBH and BOD PODFH measurements.ResultsBOD PODFH %fat (27.1%) and body volume (61.5 L) were significantly lower (P ≤ 0.001) and body density (1.0379 g/cm3) significantly higher (P ≤ 0.001) than BOD PODBH %fat (28.9%), body volume (61.7 L), and body density (1.0341 g/cm3). A significant increase in body temperature (~0.6°C; P ≤ 0.001) and body moisture (0.08 kg; P ≤ 0.01) were observed between BOD PODBH and BOD PODFH. Body surface area was positively associated with the difference in %fat independent of changes in body temperature and moisture, r = 0.30, P < 0.05.ConclusionThese data demonstrate for the first time that increases in body heat and moisture result in an underestimation of body fat when using the BOD POD, however, the precise mechanism remains unidentified.