Purpose of review The current article reviews the most innovative and precise, available methods for quantification of in-vivo human body composition. Recent findings Body composition measurement methods are continuously being perfected. Ongoing efforts involve multisegmental and multifrequency bioelectrical impedance analysis, quantitative magnetic resonance for total body water, fat, and lean tissue measurements, imaging to further define ectopic fat depots. Available techniques allow for the measurement of fat, fat-free mass, bone mineral content, total body water, extracellular water, total adipose tissue and its subdepots (visceral, subcutaneous, and intermuscular), skeletal muscle, select organs, and ectopic fat depots. Summary There is an ongoing need for methods that yield information on metabolic and biological functions. Based on the wide range of measurable properties, analytical methods and known body composition models, clinicians, and scientists can quantify a number of body components and with longitudinal assessment, can track changes in health and disease with implications for understanding efficacy of nutritional and clinical interventions, diagnosis, prevention, and treatment in clinical settings. With the greater need to understand precursors of health risk beginning prior to conception, a gap exists in appropriate in-vivo measurement methods with application beginning during gestation, that is, fetal development.

Objective This study investigated changes in fat free mass (FFM) and skeletal muscle (SM) five years after surgery in participants from the Longitudinal Assessment of Bariatric Surgery-2 trial. Methods A 3-compartment model assessed FFM, and whole-body magnetic resonance imaging (MRI) quantified SM mass prior to surgery (T0), 1 year (T1), 2 years (T2), and 5 years (T5) postoperatively in 93 patients (85% female, 68% Caucasian, age 44.2 ± 11.6 yrs) who underwent gastric bypass (RYGB), sleeve gastrectomy (SLEEVE), or adjustable gastric band (BAND). Repeated-measures mixed models were used to analyze the data. Results Significant weight loss occurred across all surgical groups in females from T0 to T1. FFM loss from T0–T1 was greater after RYGB (mean±SE:−6.9±0.6 kg) than BAND (−3.5±1.4 kg; p<0.05). RYGB females continued to lose FFM (−3.3±0.7 kg; p<0.001) from T1 to T5. A subset of RYGB males and females with MRI-measured SM showed similar initial FFM loss while maintaining FFM and SM from T1 to T5. Conclusions Between 1 and 5 years following common bariatric procedures, FFM and skeletal muscle are maintained or decrease minimally. The changes observed in FFM and muscle during the follow-up phase may be consistent with aging.

Introduction: Bariatric surgery induced weight loss may reduce resting energy expenditure (REE) and fat-free mass (FFM) disproportionately thereby predisposing patients to weight regain and sarcopenia. Methods:We compared REE and body composition of African-American and Caucasian Rouxen-Y gastric bypass (RYGB) patients after surgery with a group of non-operated controls (CON). REE by indirect calorimetry; skeletal muscle (SM), trunk organs and brain volumes by MRI; and FFM by DXA, were measured at post-surgery visits and compared with CON (N=84) using linear regression models that adjusted for relevant covariates. Ns in RYGB were 50, 42, and 30 for anthropometry and 39, 27, 17 for MRI body composition at years 1, 2 and 5 after surgery, respectively.Results: Regression models adjusted for age, weight, height, ethnicity, and sex showed REE differences (RYGB minus CON; mean±s.e.): year 1 (43.2±34 kcal/d, p=0.20); year 2 (-27.9±37.3 kcal/d, p=0.46); year 5 (114.6 ±42.3 kcal/d, p=0.008). Analysis of FFM components showed that RYGB had greater trunk organ mass (~0.4 kg) and less SM (~1.34 kg) than CON at each visit. REE models adjusted for FFM, SM, trunk-organs, and brain mass showed no between group differences in REE (-15.9 ± 54.8 kcal/d, p=0.8; -46.9±64.9 kcal/d, p=0.47; 47.7±83.0 kcal/d, p=0.57, at years 1, 2 and 5, respectively). Conclusions:Post bariatric surgery patients maintain a larger mass of high-metabolic rate trunk organs than non-operated controls of similar anthropometrics. Interpreting REE changes after weight loss requires an accurate understanding of fat-free mass composition at both the organ and tissue level.

Objective: Reliable and simple methods to quantify visceral adipose tissue (VAT) and VAT changes are needed. This study investigated the validity of dual-energy x-ray absorptiometry (DXA) compared with magnetic resonance imaging (MRI) for estimating VAT cross sectionally and longitudinally after surgery-induced weight loss in women with severe obesity.Methods: Women with obesity (n = 36; mean age 43 [SD 10] years; 89% White) with DXA and MRI before bariatric surgery (T0) at 12 (T12) and 24 months (T24) post surgery were included. CoreScan (GE Healthcare, Chicago, Illinois) estimated VAT from 20% of the distance between the top of the iliac crest and the base of the skull. MRI VAT (total VAT) was measured from the base of the heart to the sacrum/coccyx on a whole-body scan.Results: Mean DXA VAT was 45% of MRI VAT at T0, 46% at T12, and 68% at T24. DXA underestimated change in MRI VAT between T0 and T12 by 26.1% (0.81 kg, p = 0.03) and by 71.7% (0.43 kg, p < 0.001) between T12 and T24. The relationship between DXA VAT and MRI VAT differed between T12 and T24 (p value for interaction = 0.03).