Body Composition Changes After Bariatric Surgery: Magnitude, Timing, and Determinants of Excessive Fat-Free Mass Loss

In obese patients, subtle variations of the hydration of soft tissues can propagate errors in bioelectrical impedance analysis (BIA) measures of body composition. Bioelectrical impedance vector analysis (BIVA) is a useful method to evaluate tissue hydration. Laparoscopic adjustable gastric banding (LAGB) is a purely restrictive bariatric surgical procedure resulting in lower fat-free mass (FFM) loss than other malabsorptive or mixed intervention. The aim of this study was to evaluate the 6- and 12-month changes in body composition in a homogeneous group of premenopausal morbidly obese women treated by LAGB by comparing the results of conventional BIA and BIVA with dual-energy X-ray absorptiometry (DXA) method. Forty-five consecutive morbidly obese patients (mean age, 35.3 +/- 9.1 years; body mass index, 34.5-48.7 kg/m(2)) were prospectively evaluated at the Endocrinology Unit of the Department of Molecular and Clinical Endocrinology and Oncology. The LAGB device (Lap-Band System; Inamed Health, Santa Barbara, CA, USA) was inserted laparoscopically. Soft tissue hydration was evaluated by BIVA; fat mass (FM) and FFM were evaluated by BIA (BIA 101 RJL, Akern Bioresearch, Firenze, Italy) and by DXA (Hologic QDR 4500A S/N 45622; Hologic Inc., Bedford, MA, USA). Pre- and postoperative BIVA vectors indicated a normal hydration in all patients. Postoperatively, the excess of body weight loss was mainly due to a decrease in FM. The regression analysis of BIA and DXA methods at baseline and at the 6- and 12-month follow-up for FM r (2) values were 0.98, 0.94, and 0.99, respectively (p < 0.001); FM% r (2) values were 0.91, 0.89, and 0.98, respectively (p < 0.001); and FFM r (2) values were 0.87, 0.82, 0.99, respectively (p < 0.001). BIA and DXA measurements of body composition exhibit a high relative agreement in the study group of normo-hydrated obese subjects. BIA tends to overestimate FFM, but this effect is reduced along with the weight loss during the follow-up. Under the stable hydration, the BIA method may be useful as an alternative to DXA in a selected clinical setting when repeated comparisons of body composition are required.

Changes in body composition and Basic Metabolic Rate (BMR) following bariatric surgery

ObjectivesSarcopenia refers to the involuntary loss of skeletal muscle and is a predictor of physical disability/mortality. Its pathogenesis is poorly understood, although roles for altered hypoxic signaling, oxidative stress, adipokines and inflammatory mediators have been suggested. Sarcopenia also occurs upon exposure to the hypoxia of high altitude. Using data from the Caudwell Xtreme Everest expedition we therefore sought to analyze the extent of hypoxia-induced body composition changes and identify putative pathways associated with fat-free mass (FFM) and fat mass (FM) loss. MethodsAfter baseline testing in London (75m), 24 investigators ascended from Kathmandu (1300m) to Everest base camp (EBC 5300m) over 13 days. Fourteen investigators climbed above EBC, eight of whom reached the summit (8848m). Assessments were conducted at baseline, during ascent and after one, six and eight week(s) of arrival at EBC. Changes in body composition (FM, FFM, total body water, intra- and extra-cellular water) were measured by bioelectrical impedance. Biomarkers of nitric oxide and oxidative stress were measured together with adipokines, inflammatory, metabolic and vascular markers. ResultsParticipants lost a substantial, but variable, amount of body weight (7.3±4.9kg by expedition end; p<0.001). A progressive loss of both FM and FFM was observed, and after eight weeks, the proportion of FFM loss was 48% greater than FM loss (p<0.008). Changes in protein carbonyls (p<0.001) were associated with a decline in FM whereas 4-hydroxynonenal (p<0.001) and IL-6 (p<0.001) correlated with FFM loss. GLP-1 (r=−0.45, p<0.001) and nitrite (r=−0.29, p<0.001) concentration changes were associated with FFM loss. In a multivariate model, GLP-1, insulin and nitrite were significant predictors of FFM loss while protein carbonyls were predicted FM loss. ConclusionsThe putative role of GLP-1 and nitrite as mediators of the effects of hypoxia on FFM is an intriguing finding. If confirmed, nutritional and pharmacological interventions targeting these pathways may offer new avenues for prevention and treatment of sarcopenia.

Laparoscopic Roux-en-Y gastric bypass (LRYGBP) is currently the most common bariatric procedure and results in a substantial weight loss and recovery from obesity-related comorbidities, both of which are maintained in the long term. However, besides the desired loss of fat mass, LRYGBP is also followed by the loss of fat-free mass (FFM). We aimed to determine the factors associated with the loss of ≥20% of the initial FFM 1year after LRYGBP in a prospective series of 115 Caucasian, premenopausal women. Anthropometrics, body composition (bioelectrical impedance analysis), resting energy expenditure (REE) (indirect calorimetry), inflammation, insulin resistance, and lipid disturbances were determined before and 1year after LRYGBP. The mean loss of initial FFM was 15.3±13.8%. 1year after LRYGBP, 81 women lost <20% (<20% FFM group) and 35 lost ≥20% (≥20% FFM group) of the initial FFM. Before surgery, the FFM, weight, BMI, excess BMI, brachial circumference, waist circumference, and REE were significantly higher in the ≥20% FFM group while inflammation, insulin resistance, and lipid disturbances were comparable between the two groups. 1year after LRYGBP, the FFM, weight, BMI, excess BMI, brachial circumference, waist circumference, and REE decreased significantly and were comparable between the two groups. Inflammation, insulin resistance, and lipid disturbances improved comparably between the two groups after surgery. The only variable associated with the loss of ≥20% of the initial FFM in the multivariable analysis was the presence of more FFM before surgery (67.0±9.9 vs. 53.5±6.7kg). One year after LRYGBP the loss of ≥20% of the initial FFM occurred mainly in women with more FFM before surgery and resulted in the same body composition of women who lost <20% of the initial FFM.

Introduction: in patients with severe and morbid obesity it has been observed that bioimpedance (BIA) assessment generates an underestimation of fat mass (FM) and weight loss as FM after bariatric surgery, overestimating the loss of fat-free mass (FFM) and muscle mass. Objective: to evaluate the reliability of bioelectrical impedance analysis (BIA) to estimate total body water (TBW), fat-free mass (FFM), fat mass (FM), and its changes after 6 months of a Roux-en-Y gastric bypass (RYGBP), in patients with severe and morbid obesity. Methods: thirty-six patients approved for RYGBP were prospectively studied. TBW was measured by deuterium (D), and FM and FFM were calculated. A dual-frequency BIA device (5 and 200 kHz) (Bodystat Dualscan®) was used to estimate FM, FFM, TBW, extracellular water (ECW), intracellular water (ICW), and ECW/ICW ratio. Results: before RYGBP, BIA overestimated TBW by 2.6 ± 4.3 L (p = 0.002) and FFM by 3.5 ± 5.7 kg (p = 0.002), and underestimated FM% by 2.98 ± 4.7% (p = 0.002). The ECW/ICW ratio showed a significant and positive correlation with the difference BIA-D for FFM (r = 0.49; p = 0.002). After surgery, the differences between BIA and D were not significant, and the estimation error of FFM did not correlate with the ECW/ICW ratio. Conclusions: BIA generates an underestimation of FM as reported in patients with severe and morbid obesity, which is attenuated after weight reduction, underestimating weight loss as FM and overestimating FFM loss. Future research may assess whether these errors are reproduced by other BIA devices.

Adverse increases in adiposity and reductions in fat free mass (FFM) are age related changes in body composition and are linked to declines in physical function in older women. Higher protein intake in weight loss may augment fat mass (FM) loss and attenuate FFM loss, which may benefit function. This study assessed effects of 6 mo weight loss supplemented with powdered protein or placebo on body composition and function in older obese women. Women (63.8±3.4 yrs, BMI 32.9±4.1 kg/m2) were prescribed an energy‐restricted diet (1500 kcal/d; 15, 65, 30% of energy from protein, CHO and fat, respectively) and randomly assigned to 2 × 25g/d of whey protein (PRO, n=8) or maltodextrin (CARB, n=7) supplementation. Measures included whole body FM and FFM with DXA; thigh muscle, subcutaneous (SUBQ), intermuscular and intramyocellular fat with MRI; knee extension and flexion strength with isokinetic dynamometry. PRO trended towards greater weight loss (−10.6±6.7%, −5.0±4.0%; p=0.078), had greater reductions in FM (−18.9±10.6%, −8.0±4.2%; p=0.024) than CARB, but no significant difference in FFM (−4.0±4.9%, −2.0±4.1%; p=0.414). %SUBQ thigh fat change (−6.1±3.0%, −1.3±1.7%; p=0.003) was the only significant MRI outcome. Groups did not differ in leg strength changes. Higher protein intake in weight loss in older women enhances FM reductions while preserving FFM; however, these changes do not impact changes in physical function.Grant Funding Source: National Dairy Council, Carraway Foundation

The aim of this study was to determine the effects of bariatric surgery and weight loss on body composition, serum sclerostin and physical performance. Seventy-three consecutive patients (36 non-surgical controls and 37 who underwent bariatric surgery) were evaluated by means of laboratory tests, multifrequency bioelectrical impedance analysis (BIA), total-body dual-energy X-ray absorptiometry (DXA), gait speed and handgrip strength. The differences between non-surgical and surgical patients were as follows: body mass index (BMI) 42.9 ± 5.7 vs 34.8 ± 6.0kg/m2 (p < 0.001); handgrip strength 31.3 ± 7.0 vs 27.1 ± 9.3kg (p < 0.033); skeletal muscle mass index (SMI)-BIA 12.3 ± 1.2 vs 10.6 ± 1.2kg/m2; fat-free mass index (FFMI)-BIA 21.9 ± 1.9 vs 18.9 ± 2.1k/m2 (p < 0.001 for all comparisons); Baumgartner-DXA 10.8 ± 1.5 vs 9.0 ± 1.4kg/m2 (p < 0.001); fat mass BIA 55.4 ± 12.5 vs 36.8 ± 9.6; fat mass DXA 54.3 ± 12.38 vs 35.1 ± 7.5kg (p < 0.001 for both comparisons) and serum sclerostin 30.9 ± 31.9 vs 26.9 ± 21.1pmol/L (p = 0.516). Positive correlation was found between BIA and DXA: SMI × Baumgartner (r = 0.842; p < 0.001) and fat mass (r = 0.970; p < 0.001). Gait speed was relatively preserved in sleeve gastrectomy (SG) compared with Roux-en-Y gastric bypass (RYGB) (1.2 ± 0.3 and 0.9 ± 0.1m/s; p = 0.038). Bariatric surgery leads to lower values of lean and fat mass and of handgrip strength with no differences in serum sclerostin concentrations. There was a positive correlation between BIA and DXA for fat and lean mass parameters. Physical performance was better after SG than in RYGB.

Age‐related alterations in whole body composition, particularly, reduced fat free mass (FFM) and increased fat mass (FM), lead to a progressive decline in resting energy expenditure (REE). Similarly, regional body composition and fat distribution changes with age might also contribute to an overall lower REE. This study investigated the influence of age on REE, regional body composition and fat distribution, including subcutaneous fat (SF) and visceral fat (VF), in a Chinese Han population as well as their contributions to age‐related changes in REE. One hundred and two males aged 31–83 years old underwent dual‐energy X‐ray absorptiometry (DXA) which measured whole body and regional FM and FFM. SF and VF were measured by magnetic resonance imaging (MRI) and REE by indirect calorimetry. Age was significantly negatively correlated with REE (r = −0.37), total FFM (r = −0.25), upper limbs FFM (r = −0.32), lower limbs FFM (r = −0.34) and showed positive association with trunk FFM (β=0.926). FM, SF and VF decreased in older age groups after an initial rise up to 55–65 years. REE correlated positively to FM, FFM, SF, VF and showed significant association with age (β = −0.254) independent of age‐associated changes in body composition. The regional alterations in body composition with age were explained by changes in trunk FFM (β = 0.926). Age‐related decline in REE were not solely due to alterations in FM and FFM. Therefore, the changes in regional body composition, fat distribution and REE which occur during aging could be explained by disparities in race, ethnicity, diet, physical activity, and lower specific metabolic rates of FFM components.

The association of bariatric surgery and newer glucagon-like peptide-1 receptor agonists (GLP-1RAs; semaglutide and tirzepatide) with body composition still lack evidence from clinical settings. To examine temporal changes in fat-free mass (FFM), fat mass (FM), and FFM to FM ratio after bariatric surgery or GLP-1RA treatment over 24 months. This retrospective cohort study used electronic health records from Vanderbilt University Medical Center of 1257 patients aged 18 to 65 years who underwent first-time bariatric surgery from November 21, 2017, to July 21, 2022, without GLP-1RA treatment from 1 year before to 2 years after surgery, and 1809 nonsurgical patients who started semaglutide or tirzepatide between November 12, 2018, and December 6, 2023, with 2 or more prescriptions or 5% or more weight loss. All patients had 2 or more bioelectrical impedance analysis measures and no history of end-stage kidney disease or congestive heart failure. Bariatric surgery or GLP-1RA (semaglutide or tirzepatide) treatment. Relative changes in FFM, FM, and FFM to FM ratio over 24 months, controlling for age, sex, race, baseline body mass index (BMI), diabetes history, treatment year, time (restricted cubic splines), and time spline-by-treatment interaction. The study comprised 3066 patients: 1257 in the surgery group (mean [SD] age, 43.4 [10.3] years; mean [SD] baseline BMI, 46.8 [7.1]; 1033 women [82.2%]) and 1809 in the GLP-1RA group (mean [SD] age, 45.4 [11.3] years; mean [SD] baseline BMI, 41.0 [7.9]; 1457 women [80.5%]). Adjusted mean relative FM reductions in the surgery group were 42.4% (95% CI, 41.5%-43.2%) at 6 months, 49.7% (95% CI, 48.8%-50.6%) at 12 months, and 49.7% (95% CI, 47.8%-51.5%) at 24 months; reductions in the GLP-1RA group were 10.3% (95% CI, 9.5%-11.0%) at 6 months, 17.3% (95% CI, 16.5%-18.1%) at 12 months, and 18.0% (95% CI, 16.4%-19.7%) at 12 months. Adjusted mean relative FFM reductions in the surgery group were 7.8% (95% CI, 7.2%-8.4%) at 6 months, 10.6% (95% CI, 10.0%-11.2%) at 12 months, and 11.7% (95% CI, 10.4%-12.9%) at 24 months; reductions in the GLP-1RA group were 1.8% (95% CI, 1.3%-2.4%) at 6 months, 3.0% (95% CI, 2.4%-3.5%) at 12 months, and 3.3% (95% CI, 2.1%-4.4%) at 24 months. FFM to FM ratios increased significantly in both groups, with surgical patients maintaining a higher ratio throughout: the FFM to FM ratios in the surgery group were 1.8 (95% CI, 1.8-1.8) at 6 months, 2.1 (95% CI, 2.1-2.1) at 12 months, and 2.0 (95% CI, 2.0-2.1) at 24 months; the FFM to FM ratios in the GLP-1RA group were 1.4 (95% CI, 1.4-1.4) at 6 months, 1.5 (95% CI, 1.4-1.5) at 12 months, and 1.5 (95% CI, 1.5-1.6) at 24 months. Similar trends were observed in stratified analyses by sex, race, baseline BMI, baseline diabetes status, and GLP-1RA treatment duration, although men showed better FFM preservation than women, especially after GLP-1RA treatment. In this single-center cohort study, both bariatric surgery and semaglutide or tirzepatide treatment were associated with substantial FM loss, moderate FFM loss, and improved FFM to FM ratio. These findings provide evidence to guide interventions aimed at preserving FFM while promoting fat loss.

Insulin is used commonly in Type 2 diabetes and is often accompanied by weight gain. The composition of this weight gain is poorly understood. Predominant increases in fat mass could increase cardiovascular risks. The aim of the study was to evaluate insulin-induced body composition changes. Body weight and composition of 35 Type 2 diabetic patients during their first 6 months of insulin therapy was compared with those in 34 Type 2 diabetic individuals treated with insulin for at least 1 year prior to commencing the study. Body composition was determined by the simultaneous measurement of body water spaces and body density. Over 6 months, glycaemic control improved in the new treatment group only (HbA(1c): 7.26 +/- 0.81 vs. 9.66 +/- 1.60%; P < 0.0001), remaining stable in the previously treated group (7.67 +/- 1.25 vs. 7.76 +/- 1.26%; P = NS). Weight significantly increased over time in the newly treated group (+1.7 kg; P = 0.04), but not in the previously treated group (-0.3 kg). It comprised of both fat (+0.85 kg) and fat-free mass (+0.55 kg). Total body water remained unchanged. Using bioelectrical impedance analysis, the gain in fat mass was +2.2 kg; P = 0.048. Over 6 months, insulin therapy leads to a weight gain of 1.7 kg because of an increase in both fat and fat-free mass. When body composition is determined by bioelectrical impedance analysis, the results are biased by fluctuations in hydration.

BackgroundBariatric surgery (BS) is an effective treatment for obesity, but it often leads to significant changes in body composition, including loss of fat-free mass (FFM). Nutritional intake plays a crucial role in influencing these changes. This systematic review aims to assess the impact of nutritional strategies on body composition, specifically FFM preservation, following BS.MethodsA systematic literature search was conducted across PubMed, Scopus, EMBASE, Web of Science, and Google Scholar using combinations of terms including ("bariatric surgery" OR "RYGB" OR "sleeve gastrectomy") AND ("nutritional intake" OR "dietary factors") AND ("lean body mass" OR "fat-free mass" OR "body composition"). We included studies examining adults who underwent bariatric surgery and reported quantitative relationships between postoperative nutritional intake (assessed through dietary records, recalls, or biomarkers) and changes in LBM/FFM. Data were extracted and synthesized to evaluate the effects of specific nutritional factors including protein quantity/quality, macronutrient distribution, and micronutrient status on body composition outcomes.ResultsInadequate protein intake (< 60 g/day or < 1.2 g/kg ideal body weight) was common post-BS and associated with significant FFM loss (5–15% reduction). Higher protein intake (≥ 60 g/day or ≥ 1.2 g/kg) preserved FFM, particularly during the first 6 months, though results varied due to differences in study design and assessment methods. Macronutrient analysis revealed carbohydrate intake > 130 g/day correlated with poorer weight loss outcomes, while fat intake > 60 g/day was associated with greater FFM loss (2–4% additional reduction). Conversely, fiber intake > 25 g/day demonstrated protective effects. One trial of the Dietary Approaches to Stop Hypertension (DASH) diet demonstrated mixed body composition impacts.ConclusionAdequate protein intake is crucial for minimizing FFM loss after BS. Personalized nutrition plans, early counseling, and regular follow-ups are vital for improving long-term outcomes. However, variability in study results highlights the need for more research to develop standardized nutritional guidelines for post-surgery care.

Background: The effects of low-intensity, community-based aerobic exercises such as slow-jogging and walking on body composition and bone health in older women remain unclear. This study directly compared 24 weeks of slow-jogging and walking in women aged ≥70 years, focusing on changes in whole-body and regional body composition measured by dual-energy X-ray absorptiometry (DEXA), android/gynoid fat distribution, trunk-to-total fat ratio, and bone mineral density (BMD).<br/>Methods: Community-dwelling older women aged ≥70 years participated in a 24-week supervised program (60 min per session, 3 sessions per week) of either slow-jogging or walking. DEXA assessments were conducted before and after the intervention. Two-way repeated-measures ANOVA was used to examine group × time interactions, and paired t-tests were applied for within-group comparisons. Effect sizes were expressed as partial eta squared (η²) and Cohen’s d.<br/>Results: No significant group × time interactions were observed for any body composition or BMD parameters (all p > .05). Within-group analyses revealed that the slow-jogging group showed significant improvements in several outcomes, including decreases in total body mass ( p < .001) and increases in total lean mass ( p = .002), leg lean mass ( p = .009), and fat-free mass ( p < .001). The slow-jogging group also demonstrated significant gains in whole-body BMD ( p = .014) and T-score ( p = .012). In contrast, the walking group showed no significant pre–post changes except for a decrease in android lean mass ( p = .024). Some sites such as the spine exhibited borderline within-group changes ( p = .050), but no significant between-group differences were detected.<br/>Conclusion: In women aged ≥70 years, both slow-jogging and walking were safe, feasible, and maintained overall body composition over 24 weeks. Slow-jogging, despite its low intensity, produced significant within-group increases in leg lean mass, whole-body BMD, and T-score, suggesting potential regional benefits for lower-limb muscle and bone. However, large-scale reductions in fat mass or changes in regional fat distribution were limited. Clinically, slow-jogging may serve as a practical, low-impact alternative to walking for maintaining musculoskeletal health in older women, while combining aerobic exercise with resistance training and adequate protein intake may be necessary to elicit larger body composition and skeletal adaptations.

Spinal cord injury (SCI) induces dramatic changes in body composition including reductions in fat-free mass (FFM) and increases in fat mass (FM).ObjectiveTo examine changes in body composition in response to chronic activity-based therapy (ABT) in persons with SCI.DesignLongitudinal exercise intervention.MethodsSeventeen men and women with SCI (mean age = 36.1 ± 11.5 years) completed 6 months of supervised ABT consisting of load bearing, resistance training, locomotor training, and functional electrical stimulation. At baseline and after 3 and 6 months of ABT, body weight, body fat, and FFM were assessed using dual-energy X-ray absorptiometry, and fasting blood samples were obtained to assess changes in insulin-like growth factor-I (IGF-I), adiponectin, and myostatin.ResultsAcross all subjects, there was no change (P > 0.05) in body weight, percent body fat, or FFM of the leg, arm, or trunk, whereas whole-body FFM declined (P = 0.02, 50.4 ± 8.4 to 49.2 ± 7.4 kg). No changes (P = 0.21–0.41) were demonstrated in IGF-I, adiponectin, or myostatin during the study.ConclusionsChronic ABT focusing on the lower extremity does not slow muscle atrophy or alter body fat, body mass, or regional depots of FFM in persons with SCI. Further, it does not induce beneficial changes in adiponectin, myostatin, or IGF-I. Alternative exercise-based therapies are needed in SCI to reverse muscle atrophy and minimize the onset of related health risks.

Limited studies have explored the longitudinal alterations of fat-free mass (FFM), fat mass (FM), and phase angle (PhA) in the motor neuron disease (MND) population. This pilot longitudinal study investigated body composition changes via bioimpedance analysis (BIA) at time of diagnosis and gastrostomy. Nineteen patients (n = 11, 57.9% females) were included. Statistically significant reductions in FFM [median (IQR) 43.0 (17.8) kg to 42.1 (16.7) kg, p < 0.001] and PhA [4.6 (2.0)° to 4.5 (2.1)°, p = 0.012] were found. FFM (p = 0.007, 95% CI 0.505, 1.32) and FM (p = 0.024, 95% CI 0.160, 1.249) were significant predictors of weight change, with FFM accounting for 72% of the change. Larger longitudinal studies are needed to explore the clinical benefit associated with reducing pre-gastrostomy FFM loss in the MND population. In the interim, clinicians should consider monitoring body composition and implementing interventions aimed at preserving body weight and composition, particularly FFM, prior to gastrostomy placement.

Changes in body composition after renal transplantation (RTx) are of clinical significance, since increments in fat mass may contribute to glucose intolerance and cardiovascular morbidity. The aim of this study was to quantify the early changes in body composition after transplantation and identify predictors of these changes. Total and regional body composition of 102 first kidney allograft recipients were measured at transplantation and after 10 weeks using dual-energy X-ray absorptiometry. The population comprised a high proportion of pre-emptive and well-nourished kidney recipients. Multiple linear regression was used to identify predictors of change. Mean fat mass was 27.1+/-8.7% of body weight at baseline. The fat mass percentage increased by 2.2% corresponding to a 1.3 kg increase in fat mass at 10 weeks (p< 0.001). Fat-free mass declined by 2.5 kg (p<0.001), with no significant loss of body weight (0.9 kg, p=0.11). Age, low-tertile fat mass, plasma C-reactive protein, time on dialysis and cumulative prednisolone dose were independent predictors (p<0.05) of the increase in fat mass. Cumulative prednisolone dose was the only significant predictor of decrease in fat-free mass. Essentially the same results were found for both genders. A significant increase in fat mass occurred rapidly after RTx along with a reduction in fat-free mass despite stable body weight. Early fat mass accumulation may predispose to comorbidity, but the long-term clinical significance of these early changes remains to be explored in prospective studies.