Comparison of dual-energy X-ray absorptiometry, air displacement plethysmography and bioelectrical impedance analysis for the assessment of body composition in morbidly obese women

Body composition assessment in individuals with class II/III obesity: a narrative review

BACKGROUND

Individuals with class II/III obesity have a high percentage of body fat. Assessing body composition in cases of severe obesity can be difficult and controversial both in clinical practice and scientific research. Thus, it is essential to explore the different aspects of evaluating body composition and to discuss the available methods to assess it in this population.

AIMS

To summarise and discuss the methods used to measure body composition in adults with class II/III obesity and their potential in clinical practice and scientific research.

METHODS

This is a narrative review using data from PubMed, Scielo, and Lilacs databases. Original articles on body composition analysis in adults with class II/III obesity i.e., a BMI ≥ 35 kg/m2 were eligible. Body composition assessment methods were analysed and described.

RESULTS

Some imaging methods produced significantly accurate results. Dual-energy X-ray absorptiometry (DXA) significantly produces accurate results and has been used in clinical studies. However, due to its high cost, it is not applicable in clinical practice. Multifrequency bioelectrical impedance analysis (BIA) has good accuracy and is more appropriate for clinical practice than other methods. We have highlighted several aspects of the importance and applicability of performing body composition analysis in individuals with class II/III obesity.

CONCLUSION

DXA has been considered the most adequate method for clinical research. Multifrequency BIA may be a viable alternative to DXA for use in clinical practice. Assessing body composition and its components is important for people with class II/III obesity. It can help improve the effectiveness of interventions and clinical treatments, especially in reducing the risk of losing muscle mass. Muscle loss can cause sarcopenic obesity and other clinical complications, so understanding body composition is crucial. Assessing body composition can also help understand the impact of interventions on bones and avoid clinical complications.

Characterization of Circulating Protein Profiles in Individuals with Prader-Willi Syndrome and Individuals with Non-Syndromic Obesity

Background: Prader-Willi syndrome (PWS) is a rare genetic disorder characterized by distinctive physical, cognitive, and behavioral manifestations, coupled with profound alterations in appetite regulation, leading to severe obesity and metabolic dysregulation. These clinical features arise from disruptions in neurodevelopment and neuroendocrine regulation, yet the molecular intricacies of PWS remain incompletely understood. Methods: This study aimed to comprehensively profile circulating neuromodulatory factors in the serum of 53 subjects with PWS and 34 patients with non-syndromic obesity, utilizing a proximity extension assay with the Olink Target 96 neuro-exploratory and neurology panels. The ANOVA p-values were adjusted for multiple testing using the Benjamani-Hochberg method. Protein-protein interaction networks were generated in STRING V.12. Corrplots were calculated with R4.2.2 by using the Hmisc, Performance Analytics, and Corrplot packages Results: Our investigation explored the potential genetic underpinnings of the circulating protein signature observed in PWS, revealing intricate connections between genes in the PWS critical region and the identified circulating proteins associated with impaired oxytocin, NAD metabolism, and sex-related neuromuscular impairment involving, CD38, KYNU, NPM1, NMNAT1, WFIKKN1, and GDF-8/MSTN. The downregulation of CD38 in individuals with PWS (p < 0.01) indicates dysregulation of oxytocin release, implicating pathways associated with NAD metabolism in which KYNU and NMNAT1 are involved and significantly downregulated in PWS (p < 0.01 and p < 0.05, respectively). Sex-related differences in the circulatory levels of WFIKKN1 and GDF-8/MSTN (p < 0.05) were also observed. Conclusions: This study highlights potential circulating protein biomarkers associated with impaired oxytocin, NAD metabolism, and sex-related neuromuscular impairment in PWS individuals with potential clinical implications.

Serum proteome signatures associated with liver steatosis in adolescents with obesity

PURPOSE

Childhood obesity, a pressing global health issue, significantly increases the risk of metabolic complications, including metabolic dysfunction associated with steatotic liver disease (MASLD). Accurate non-invasive tests for early detection and screening of steatosis are crucial. In this study, we explored the serum proteome, identifying proteins as potential biomarkers for inclusion in non-invasive steatosis diagnosis tests.

METHODS

Fifty-nine obese adolescents underwent ultrasonography to assess steatosis. Serum samples were collected and analyzed by targeted proteomics with the Proximity Extension Assay technology. Clinical and biochemical parameters were evaluated, and correlations among them, the individuated markers, and steatosis were performed. Receiver operating characteristic (ROC) curves were used to determine the steatosis diagnostic performance of the identified candidates, the fatty liver index (FLI), and their combination in a logistic regression model.

RESULTS

Significant differences were observed between subjects with and without steatosis in various clinical and biochemical parameters. Gender-related differences in the serum proteome were also noted. Five circulating proteins, including Cathepsin O (CTSO), Cadherin 2 (CDH2), and Prolyl endopeptidase (FAP), were identified as biomarkers for steatosis. CDH2, CTSO, Leukocyte Immunoglobulin Like Receptor A5 (LILRA5), BMI, waist circumference, HOMA-IR, and FLI, among others, significantly correlated with the steatosis degree. CDH2, FAP, and LDL combined in a logit model achieved a diagnostic performance with an AUC of 0.91 (95% CI 0.75-0.97, 100% sensitivity, 84% specificity).

CONCLUSIONS

CDH2 and FAP combined with other clinical parameters, represent useful tools for accurate diagnosis of fatty liver, emphasizing the importance of integrating novel markers into diagnostic algorithms for MASLD.

Prediction of resting energy expenditure in Italian older adults with severe obesity

Background

In the last decade a large number of studies proposed and/or validated equations to estimate the Resting Energy Expenditure (REE) in adults and/or older adults, however, no equation currently available showed good accuracy for older adults with severe obesity. Thus, this study aimed to develop and validate new predictive equations for REE, based on data from the indirect calorimetry, in Italian older adults with severe obesity.

Methods

A retrospective study was as conducted with 764 Caucasian older adults with severe obesity (age range: 60-74 years and BMI ≥ 35 kg/m/²). Four models were used to test the accuracy of anthropometry and body composition variables in multivariable prediction of REE. All models were derived by stepwise multiple regression analysis using a calibration group of 382 subjects [295 females and 87 males] and the equations were cross-validated in the remaining 382 subjects [295 females and 87 males] as validation group. The new prediction equations and the other published equations were tested using the Bland-Altman method. Prediction accuracy was defined as the percentage of subjects whose REE was predicted within ± 10% of measured REE.

Results

All the equations analyzed predicted higher energy requirements for males than females, and most of them underestimated the energy requirement values of our sample. The highest accuracy values were observed in the new equations, with 62% in the anthropometric model and 63% in the body composition model.

Conclusion

Although the accuracy of our equations was slightly higher in comparison with the other taken into consideration, they cannot be considered completely satisfactory for predicting REE in Italians older adults with severe obesity. When predicting equations cannot guarantee precise or acceptable values of REE, the use of indirect calorimetry (if available) should be always recommended, especially in clinical practice.

Cardiometabolic Index (CMI) and Visceral Adiposity Index (VAI) Highlight a Higher Risk of Metabolic Syndrome in Women with Severe Obesity

Recent evidence shows that simple and inexpensive anthropometric measurements can be used to identify, at an early stage, women with obesity at increased risk of developing metabolic syndrome (MetS). Thus, the aim of this study was to compare the accuracy of five different indexes of adiposity and/or body composition in identifying MetS in a group of 876 women (mean age ± SD: 52.1 ± 13.8 years; body mass index (BMI): 43.6 ± 6.1 kg m^-2). The following indexes were determined for each subject: waist-to-hip ratio (WHR), waist-to-height ratio (WtHR), body mass fat index (BMFI), visceral adiposity index (VAI), and cardiometabolic index (CMI). Overall, the presence of MetS was detected in 544 patients (62%). Pearson correlation coefficients were calculated to evaluate the relationships between body composition indexes and metabolic characteristics of the women. Receiver operating characteristic (ROC) analysis was used to determine the best predictor for each adiposity index among metabolic risk factors. The ROC analysis showed VAI (AUC = 0.84) and CMI (AUC = 0.86) showed the best performance in predicting MetS. Differences were found between the ROC area of CMI and VAI with all other indexes (p < 0.05). The optimal cutoff point for early diagnosis of MetS was >0.92 for WHR, >0.76 for WtHR, >30.1 kg m^-1 for BMFI, >1.94 for VAI, and >0.84 for CMI. In addition, VAI and CMI were the most sensitive and specific indexes compared with other indexes. In conclusion, VAI and CMI represent the most useful and reliable indexes to be used for detecting MetS in women suffering from obesity in clinical practice.

The Role of Different Indexes of Adiposity and Body Composition for the Identification of Metabolic Syndrome in Women with Obesity

The aim of this study was to compare the accuracy of different indexes of adiposity and/or body composition in identifying the metabolic syndrome (MetS) in a group of 1528 Caucasian women with obesity: (age ± standard deviation (SD): 50.8 ± 14 years (range 18–83); body mass index (BMI) 43.3 ± 5.9 kg/m² (30.7–72.9 kg/m²)). The following indexes were assessed in each subject: BMI, fat-free mass index (FFMI), fat mass index (FMI), tri-ponderal mass index (TMI), waist-to-height ratio (WtHR), and the body mass fat index (BMFI). Thereafter, a threshold value adjusted for age, which could identify MetS, was calculated for each index. A significant correlation was found among all indexes (p < 0.0001 for all). However, when the area under the curve (AUC) was compared, WtHR performed significantly better in the whole group and in the different age groups, apart from a lack of statistical difference between WtHR and BMFI in the 45–55 years age group. In conclusion, WtHR seems to be a fair index useful for identifying MetS in women with obesity. The use of thresholds appropriate for age can help further improve its accuracy, thus reinforcing the clinical evaluation for MetS screening.

Evaluation of multi-frequency bioelectrical impedance analysis for the assessment of body composition in individuals with obesity

OBJECTIVE

The purpose of this study was to compare body composition measurements estimated by multi-frequency bioelectrical impedance analysis (MF-BIA) with air displacement plethysmography (ADP) in individuals with obesity.

METHODS

Bariatric patients were recruited from Geisinger's Center for Nutrition and Weight Management Clinic in Danville, Pennsylvania. Sixty-two participants (age = 52.4 ± 9.3 years; body mass index = 38.9 ± 8.0 kg m-2) reported for a same-day testing visit. Body composition was measured using a common MF-BIA analyzer (InBody 720, Biospace Co., Beverly Hills, CA) and ADP.

RESULTS

Strong relationships were observed between MF-BIA and ADP methods (r = 0.88-0.96, P < 0.001). There were no differences between MF-BIA and ADP measures of per cent body fat, fat mass or fat-free mass for the total sample or when examined by gender.

CONCLUSIONS

The InBody 720 MF-BIA analyzer produced body composition measurements that were similar to ADP supporting the use of this technology in the obese population.

Assessment of fat-free mass from bioelectrical impedance analysis in men and women with Prader-Willi syndrome: cross-sectional study

We have recently shown that population-specific formulae are required to estimate fat-free mass (FFM) from bioelectrical impedance analysis (BIA) in obese women with Prader-Willi syndrome (PWS) matched by age and percent fat mass (FM) to non-PWS women. The present cross-sectional study was aimed at developing generalised BIA equations that could be used in PWS subjects independently of sex and FM. We used dual-energy X-ray absorptiometry to measure FFM and BIA to measure whole-body impedance at 50 kHz (Z₅₀) in 34 women and 21 men with PWS. The impedance index, that is, height (cm)²/Z₅₀ (Ω), explained 77% (BCa-bootstrapped 95% CI 65 to 85%) of the variance of FFM with a root mean squared error of the estimate of 3.7 kg (BCa-bootstrapped 95% CI 3.2 to 4.5 kg). BIA can be used to estimate FFM in obese and non-obese PWS men and women by means of population-specific equations.

Dietary source of saturated fat and percentage body fat of patients with type 2 diabetes mellitus: A cross-sectional study

BACKGROUND

The influence of dietary fat on the body fat of patients with diabetes is not well established. This cross-sectional study aimed to analyze the association between percentage body fat (PBF) and dietary sources of fat from the usual diet of patients with type 2 diabetes.

METHODS

Outpatients were submitted to PBF evaluation estimated by bioelectrical impedance. The patient's usual diet was assessed by a 3-day weighed diet record (WDR), and compliance was analyzed by comparing the protein intake estimated from the WDR and that from 24-hr urinary nitrogen output.

RESULTS

A total of 188 patients with type 2 diabetes (aged 62.5 ± 8.8 years; 57% female, body mass index [BMI] 29.3 ± 3.8 kg/m²) were analyzed and divided into groups with high and low PBF according to mean PBF (men: 26.6 ± 7.1%; women: 39.8 ± 5.9%). Patients with high PBF consumed an increased proportion of red meat (52.0% of total meat), processed meat (5.4%), and saturated fat from red meat (2.1% of energy) compared to low PBF individuals (42.3% [p = 0.036]; 3.0% [p = 0.010]; 1.5% of energy [p = 0.032], respectively). According to Poisson's regression, the consumption of red meat (PR = 1.008 [95% CI = 1.002-1.013]; p = 0.006) and the reuse of frying oil (PR = 1.670 [95% CI = 1.240-2.249]; p = 0.001) were associated with higher PBF. In the adjusted analysis, the upper tertile of processed meat intake was associated with higher PBF (PR = 1.522 [95% CI = 1.226-1.891]; p = 0.001) compared to the lower tertile.

CONCLUSIONS

The present study suggested that a higher ingestion of dietary sources of saturated fat was associated with high PBF in patients with type 2 diabetes.

A new anthropometric index for body fat estimation in patients with severe obesity

Background

Body mass index (BMI) has been used to assess body adiposity, but it cannot adequately reflect body fat (BF) amount. The body adiposity index (BAI) has been shown a better performance than BMI for this purpose, but it can be inaccurate to estimate BF under extreme amounts of fat. Here, we propose a new anthropometric index, the Belarmino–Waitzberg (BeW) index, for specific estimation of BF in severely obese patients.

Methods

In 144 adult patients with severe obesity, BF was estimated by air displacement plethysmography (ADP), as the reference method, along with the follow anthropometric measurements: height, abdominal circumference (AC), hip circumference (HC), weight, BMI (weight/ height²) and BAI ([HC(cm) / height (m)^1.5) − 18] × 100). Patients were proportionately distributed into two distinct databases, the building model database (BMD) and the validation model database (VMD), which were applied to develop and validate the BeW index, respectively. The BeW index was tested for gender and ethnicity adjustment as independent variables. The agreement of BF% values obtained by the new index and by BAI with ADP was also assessed.

Results

The BF% was 52.05 ± 5.42 for ADP and 59.11 ± 5.95 for the BeW index (all results are expressed as the mean ± standard deviation). A positive Pearson correlation (r = 0.74), a good accuracy (Cb = 0.94), and a positive Lin’s concordance correlation (CCC = 0.70) were observed between the two groups. The 95% limits of individual agreement between the BeW index and ADP were 6.8 to 7.9%, compared to − 7.5 to 14.8% between the BAI and ADP. The new index, called the Belarmino–Waitzberg (BeW) index, showed an improvement of 2.1% for the R² value and a significant gender effect, therefore resulting in two different indexes for females and males, as follows: Female BeW = − 48.8 + 0.087 × AC(cm) + 1.147 × HC(cm) - 0.003 × HC(cm)2 and Male BeW = − 48.8 + 0.087 × AC(cm) + 1.147 × HC(cm) - 0.003 × HC(cm)2–7.195.

Conclusions

The new BeW index showed a good performance for BF estimation in patients with severe obesity and can be superior to the BAI for this purpose.

Proportional bias between dual-energy x-ray absorptiometry and bioelectrical impedance analysis varies based on sex in active adults consuming high- and low-carbohydrate diets

Dual-energy x-ray absorptiometry (DXA) and bioelectrical impedance analysis (BIA) are common methods of body composition assessment, but the agreement between these methods varies. Bias between DXA and single-frequency BIA was evaluated at 6 different time points in 48 active male and female adults consuming standardized high- and low-carbohydrate diets. It was hypothesized that fixed and proportional biases exist between DXA and BIA but that the extent of bias does not differ based on sex. Substantial fixed bias was present for estimates obtained by DXA and BIA, and both men and women exhibited proportional bias for fat mass (FM) and fat-free mass (FFM). The magnitude of bias was greater in women, and only women exhibited proportional bias for body fat percentage. In individuals with less FM, the mean difference between DXA and BIA was high, indicating that BIA underestimated FM relative to DXA. However, in individuals with greater FM, better agreement was seen. Correspondingly, the mean difference in FFM estimates was greater in individuals with less FFM. In some individuals with high quantities of FM or FFM relative to the sample, the relationship between devices was reversed such that BIA overestimated FM and underestimated FFM. The degree of disagreement between DXA and BIA varies substantially based on body size and sex such that all-encompassing statements regarding the comparability of these technologies cannot presently be made.

Body Composition Changes After Very-Low-Calorie Ketogenic Diet in Obesity Evaluated by 3 Standardized Methods

CONTEXT

Common concerns when using low-calorie diets as a treatment for obesity are the reduction in fat-free mass, mostly muscular mass, that occurs together with the fat mass (FM) loss, and determining the best methodologies to evaluate body composition changes.

OBJECTIVE

This study aimed to evaluate the very-low-calorie ketogenic (VLCK) diet-induced changes in body composition of obese patients and to compare 3 different methodologies used to evaluate those changes.

DESIGN

Twenty obese patients followed a VLCK diet for 4 months. Body composition assessment was performed by dual-energy X-ray absorptiometry (DXA), multifrequency bioelectrical impedance (MF-BIA), and air displacement plethysmography (ADP) techniques. Muscular strength was also assessed. Measurements were performed at 4 points matched with the ketotic phases (basal, maximum ketosis, ketosis declining, and out of ketosis).

RESULTS

After 4 months the VLCK diet induced a -20.2 ± 4.5 kg weight loss, at expenses of reductions in fat mass (FM) of -16.5 ± 5.1 kg (DXA), -18.2 ± 5.8 kg (MF-BIA), and -17.7 ± 9.9 kg (ADP). A substantial decrease was also observed in the visceral FM. The mild but marked reduction in fat-free mass occurred at maximum ketosis, primarily as a result of changes in total body water, and was recovered thereafter. No changes in muscle strength were observed. A strong correlation was evidenced between the 3 methods of assessing body composition.

CONCLUSION

The VLCK diet-induced weight loss was mainly at the expense of FM and visceral mass; muscle mass and strength were preserved. Of the 3 body composition techniques used, the MF-BIA method seems more convenient in the clinical setting.

GH Responsiveness to Combined GH-Releasing Hormone and Arginine Administration in Obese Patients with Fibromyalgia Syndrome

Reportedly, fibromyalgia (FM) is frequently associated with reduced IGF-1 levels and GH hyporesponsiveness to different GH stimulation tests. Since there is a high prevalence of obesity in FM, and obesity itself is characterized by hyposomatotropism, the aim of this study was to assess IGF-1 levels and GH responsiveness in sixteen severely obese women suffering from FM, who, subdivided into two subgroups on the basis of their age-dependent IGF-1 values (> or <-2 SDS), underwent the combined GHRH plus arginine test. Four out of 16 obese women with FM (25%) had low IGF-1 SDS values, 2 cases of this subgroup (12.5%) failing also to normally respond to the test. Among patients with normal GH responses, 4 showed a delayed GH peak. The subgroup with low IGF-1 SDS values had higher BMI than that with normal IGF-1 SDS. GH peak and area under the curve were not correlated with CRP, ESR, or tender point score, while significant correlations were found with fat-free mass and fat mass. In conclusion, this study shows the existence of a high prevalence of GH-IGF-1 dysfunction in patients with both FM and obesity, presumably as a consequence of the obese rather than fibromyalgic condition.

Practical Considerations for Body Composition Assessment of Adults with Class II/III Obesity Using Bioelectrical Impedance Analysis or Dual-Energy X-Ray Absorptiometry

PURPOSE OF REVIEW

The purpose of this review is to explore the practical considerations for body composition assessment of adults with class II/III obesity. Studies assessing adults (18-64 years) with a body mass index (BMI) ≥35 kg/m² with bioelectrical impedance analysis (BIA) and/or dual-energy X-ray absorptiometry (DXA) were included.

RECENT FINDINGS

Twelve studies met inclusion criteria. Five considerations were identified: variances in equipment and technology, equipment weight capacity, subject positioning, tissue penetration, and total body hydration. In subjects with BMI ≥35 kg/m², BIA overestimated fat-free mass with scaling errors as BMI increased. DXA provided accurate and reliable body composition measures, but equipment-related barriers prevented assessment of some taller, wider, and heavier subjects. BIA is an unreliable method to assess body composition in class II/III obesity. Advancements in DXA technology (e.g., iDXA), methodology (e.g., subject positioning, longer scan times), and more inclusive testing criteria (e.g., use equipment limits not just BMI) may improve access and understanding of body composition in this cohort.

The Apparent Relation between Plasma 25-Hydroxyvitamin D and Insulin Resistance is Largely Attributable to Central Adiposity in Overweight and Obese Adults

BACKGROUND

Research indicates that plasma 25-hydroxyvitamin D [25(OH)D] is associated with insulin resistance, but whether regional adiposity confounds this association is unclear.

OBJECTIVE

This study assessed the potential influence of adiposity and its anatomical distribution on the relation between plasma 25(OH)D and insulin resistance.

METHODS

A secondary analysis of data from middle-aged overweight and obese healthy adults [n = 336: 213 women and 123 men; mean ± SD (range); age: 48 ± 8 y (35-65 y); body mass index (BMI; in kg/m2): 30.3 ± 2.7 (26-35)] from West Lafayette, Indiana (40.4 °N), were used for this cross-sectional analysis. Multiple linear regression analyses that controlled for multiple covariates were used as the primary statistical model.

RESULTS

Of all participants, 8.6% and 20.5% displayed moderate [20.1-37.5 nmol/L plasma 25(OH)D] to mild (37.6-49.9 nmol/L) vitamin D insufficiency, respectively. A regression analysis controlling for age, sex, race, plasma parathyroid hormone concentration, season of year, and supplement use showed that 25(OH)D was negatively associated with fasting insulin (P = 0.021). Additional regression analyses showed that total and central adiposity but not peripheral adiposity predicted low plasma 25(OH)D [total fat mass index (FMI): P = 0.018; android FMI: P = 0.052; gynoid FMI: P = 0.15; appendicular FMI: P = 0.07) and insulin resistance (homeostasis model assessment of insulin resistance: total and android FMI, P <0.0001; gynoid FMI, P = 0.94; appendicular FMI, P = 0.86). The associations of total and central adiposity with insulin resistance remained significant after adjusting for plasma 25(OH)D. However, adjusting for central adiposity but not other anatomical measures of fat distribution eliminated the association between plasma 25(OH)D and insulin resistance.

CONCLUSION

Central adiposity drives the association between plasma 25(OH)D and insulin resistance in overweight and obese adults. The trial was registered at clinicaltrials.gov as NCT00812409.

High velocity circuit resistance training improves cognition, psychiatric symptoms and neuromuscular performance in overweight outpatients with severe mental illness

We developed a physical exercise intervention aimed at improving multiple determinants of physical performance in severe mental illness. A sample of 12 (9M, 3F) overweight or obese community-dwelling patients with schizophrenia (n=9) and bipolar disorder (n=3) completed an eight-week, high-velocity circuit resistance training, performed twice a week on the computerized Keiser pneumatic exercise machines, including extensive pre/post physical performance testing. Participants showed significant increases in strength and power in all major muscle groups. There were significant positive cognitive changes, objectively measured with the Brief Assessment of Cognition Scale: improvement in composite scores, processing speed and symbol coding. Calgary Depression Scale for Schizophrenia and Positive and Negative Syndrome Scale total scores improved significantly. There were large gains in neuromuscular performance that have functional implications. The cognitive domains that showed the greatest improvements (memory and processing speed) are most highly predictive of disability in schizophrenia. Moreover, the improvements seen in depression suggest this type of exercise intervention may be a valuable add-on therapy for bipolar depression.

Air displacement plethysmography versus dual-energy x-ray absorptiometry in underweight, normal-weight, and overweight/obese individuals

BACKGROUND

Accurately estimating fat percentage is important for assessing health and determining treatment course. Methods of estimating body composition such as hydrostatic weighing or dual-energy x-ray absorptiometry (DXA), however, can be expensive, require extensive operator training, and, in the case of hydrostatic weighing, be highly burdensome for patients. Our objective was to evaluate air displacement plethysmography via the Bod Pod, a less burdensome method of estimating body fat percentage. In particular, we filled a gap in the literature by testing the Bod Pod at the lower extreme of the Body Mass Index (BMI) distribution.

FINDINGS

Three BMI groups were recruited and underwent both air displacement plethysmography and dual-energy x-ray absorptiometry. We recruited 30 healthy adults at the lower BMI distribution from the Calorie Restriction (CR) Society and followers of the CR Way. We also recruited 15 normal weight and 19 overweight/obese healthy adults from the general population. Both Siri and Brozek equations derived body fat percentage from the Bod Pod, and Bland-Altman analyses assessed agreement between the Bod Pod and DXA. Compared to DXA, the Bod Pod overestimated body fat percentage in thinner participants and underestimated body fat percentage in heavier participants, and the magnitude of difference was larger for underweight BMI participants, reaching 13% in some. The Bod Pod and DXA had smaller discrepancies in normal weight and overweight/obese participants.

CONCLUSIONS

While less burdensome, clinicians should be aware that Bod Pod estimates may deviate from DXA estimates particularly at the lower end of the BMI distribution.

Assessment of fat-free mass from bioelectrical impedance analysis in obese women with Prader-Willi syndrome

BACKGROUND

Fat-free mass (FFM) is lower in obese subjects with Prader-Willi syndrome (PWS) than in obese subjects without PWS. FFM prediction equations developed in non-PWS subjects may, thus, not work in PWS subjects.

AIM

To test whether the estimation of FFM from bioelectrical impedance analysis (BIA) in PWS subjects requires population-specific equations.

METHODS

Using dual-energy X-ray absorptiometry, this study measured FFM in 27 PWS and 56 non-PWS obese women and evaluated its association with the impedance index at 50 kHz (ZI50), i.e. the ratio between squared height and whole-body impedance at 50 kHz.

RESULTS

At the same level of ZI50, PWS women had a lower FFM than non-PWS women. However, when PWS-specific equations were used, FFM was accurately estimated at the population level. An equation employing a dummy variable coding for PWS status was able to explain 85% of the variance of FFM with a root mean squared error of 3.3 kg in the pooled sample (n = 83).

CONCLUSION

Population-specific equations are needed to estimate FFM from BIA in obese PWS women.

Body composition indices of a load-capacity model: gender- and BMI-specific reference curves

OBJECTIVE

Fat mass (FM) and fat-free mass (FFM) are frequently measured to define body composition phenotypes. The load-capacity model integrates the effects of both FM and FFM to improve disease-risk prediction. We aimed to derive age-, gender- and BMI-specific reference curves of load-capacity model indices in an adult population (≥18 years).

DESIGN

Cross-sectional study. Dual-energy X-ray absorptiometry was used to measure FM, FFM, appendicular skeletal muscle mass (ASM) and truncal fat mass (TrFM). Two metabolic load-capacity indices were calculated: ratio of FM (kg) to FFM (kg) and ratio of TrFM (kg) to ASM (kg). Age-standardised reference curves, stratified by gender and BMI (<25.0 kg/m2, 25.0-29.9 kg/m2, ≥30.0 kg/m2), were constructed using an LMS approach. Percentiles of the reference curves were 5th, 15th, 25th, 50th, 75th, 85th and 95th.

SETTING

Secondary analysis of data from the 1999-2004 National Health and Nutrition Examination Survey (NHANES).

SUBJECTS

The population included 6580 females and 6656 males.

RESULTS

The unweighted proportions of obesity in males and females were 25.5 % and 34.7 %, respectively. The average values of both FM:FFM and TrFM:ASM were greater in female and obese subjects. Gender and BMI influenced the shape of the association of age with FM:FFM and TrFM:ASM, as a curvilinear relationship was observed in female and obese subjects. Menopause appeared to modify the steepness of the reference curves of both indices.

CONCLUSIONS

This is a novel risk-stratification approach integrating the effects of high adiposity and low muscle mass which may be particularly useful to identify cases of sarcopenic obesity and improve disease-risk prediction.

Relationship between glucose metabolism and non-alcoholic fatty liver disease severity in morbidly obese women

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is an independent predictor of type 2 diabetes mellitus (T2DM). Insulin resistance and beta-cell dysfunction are involved in the pathogenesis of T2DM. Insulin resistance is associated with NAFLD but little is known about beta-cell dysfunction and NAFLD.

AIM

We tested whether NAFLD severity is associated with insulin sensitivity and beta-cell function in morbidly obese women.

SUBJECTS AND METHODS

We studied 61 Caucasian women aged 18-60 years without T2DM and with a body mass index ranging from 35.3 to 48.8 kg/m². The insulin sensitivity index (ISI) and the disposition index (DI) from oral glucose tolerance testing were used as measures of insulin sensitivity and beta-cell function, respectively. Fat was measured by dual-energy X-ray absorptiometry. Fatty liver was diagnosed by ultrasonography and ordinally coded as 0 = none, 1 = light, 2 = moderate, 3 = severe. Proportional-odds logistic regression was used to evaluate the association of NAFLD severity with log(e)ISI and log(e)DI with and without correction for total and truncal fat.

RESULTS

The odds of more severe vs. less severe NAFLD decreased for increasing log(e)ISI [odds ratio (OR) 0.40, 95 % CI 0.19-0.84, p < 0.05] and log(e)DI (OR 0.80, 95 % CI 0.69-0.92, p < 0.01). Neither total nor truncal fat had any effect on these associations.

CONCLUSION

In morbidly obese women, NAFLD severity is inversely associated with insulin sensitivity and beta-cell function. The association of NAFLD severity with beta-cell dysfunction is stronger than that with insulin resistance.

Inverse relationship between "a body shape index" (ABSI) and fat-free mass in women and men: Insights into mechanisms of sarcopenic obesity

BACKGROUND & AIMS

Sarcopenic obesity may be defined by a high fat to fat-free mass (FM/FFM) ratio. Skeletal muscle may be negatively influenced by the pro-inflammatory milieu associated with visceral fat, while the loading effect induced by a heavier body mass index (BMI) may enhance muscle anabolism. Recently, a new anthropometric measure based on waist circumference (A Body Shape Index, ABSI) was developed. In this study we have assessed the predictive power of ABSI on the FFM index (FFMI), a surrogate marker of lean mass.

METHODS

Standard anthropometric parameters and ABSI as well as body composition data (fat and fat-free mass determined by bioelectrical impedance analysis) were assessed in 111 female and 89 male overweight/obese subjects, with no clinically significant co-morbidities. Groups with higher- or lower-ABSI were identified according to median values of this index.

RESULTS

In women and men, ABSI did not correlate with BMI, while multiple linear regression indicated that BMI (β-coefficients: 0.62 and 0.77, respectively) and ABSI (β-coefficients: -0.26 and -0.22, respectively) independently predicted FFMI (multiple R: 0.72 and 0.83, respectively, P < 0.001). Men and women with lower-ABSI exhibited significantly greater FFMI than the higher-ABSI groups for comparable values of BMI. In men, ABSI was correlated positively with C-reactive protein (CRP) (R = 0.30; P < 0.05) and negatively with the reciprocal of insulin (R = 0.28; P < 0.05), an index of insulin sensitivity. FM/FFM ratio significantly (P < 0.01) correlated with CRP (R = 0.31) in women only.

CONCLUSIONS

ABSI, a recently introduced marker of abdominal adiposity, may contribute to define the risk of sarcopenia in overweight/obese individuals.

Is non-alcoholic fatty liver disease less frequent among women with Prader-Willi syndrome?

OBJECTIVE

Patients with Prader-Willi syndrome (PWS) have been hypothesized to be at lower risk of non-alcoholic fatty liver disease (NAFLD) because of higher insulin sensitivity. However, PWS patients have a peculiar body composition, i.e. higher fat mass and lower fat-free mass, which may confound such associations. We evaluated whether NAFLD is less frequent in PWS than in non-PWS women matched on percent body fat (PBF).

METHODS

PBF was measured by dual-energy X-ray absorptiometry. Liver fat was assessed by ultrasonography. Insulin sensitivity and beta-cell function were evaluated by oral glucose tolerance testing. Coarsened exact matching (CEM) was used to match PWS and non-PWS women on PBF. General and generalized linear models taking CEM into account were used to perform comparisons between PWS and non-PWS women.

RESULTS

20 women with PWS were matched to 27 women without PWS on the basis of PBF (mean 53 vs. 54%, p = 0.6). Insulin sensitivity and beta-cell function were similar in the two groups. However, the prevalence of NAFLD was 25% in PWS versus 59% in non-PWS women (p = 0.04).

CONCLUSION

NAFLD is less frequent in PWS than in non-PWS women but this finding is not associated with higher insulin sensitivity.