Body composition changes after bariatric surgery in adults with obesity and hepatic steatosis

Abstract

BACKGROUND

Obesity drives multiple chronic conditions, including metabolic steatotic liver disease. Bariatric surgery is effective in inducing weight loss and improving metabolic dysfunction, potentially modifying liver-related outcomes. However, short-term effects on body composition and noninvasive liver markers remain incompletely characterized. We hypothesized that bariatric surgery significantly improves body composition and metabolic parameters associated with hepatic steatosis.

AIM

To investigate body composition and liver-related biochemical changes after bariatric surgery in patients with obesity and hepatic steatosis.

METHODS

This retrospective cohort study evaluated 91 adults undergoing Roux-en-Y gastric bypass at a tertiary hospital. Data collected preoperatively and 6 months postoperatively included body composition by bioelectrical impedance analysis, laboratory tests, and noninvasive fibrosis scores. Paired Student’s t-test or Wilcoxon test was applied, with significance set at 5%.

RESULTS

Body mass index decreased significantly (e.g., 42.1 ± 5.8 kg/m² vs 32.6 ± 4.9 kg/m²; P < 0.001). Visceral fat and body fat percentage were markedly reduced (P < 0.001). Alanine aminotransferase, glucose, triglycerides, and creatinine levels declined significantly. Serum vitamin D and vitamin B12 increased (P < 0.01). Muscle and cellular mass decreased (P < 0.05). Platelet count changed modestly, while fibrosis scores remained stable.

CONCLUSION

Bariatric surgery improves body composition and metabolic markers associated with hepatic steatosis, while early fibrosis indices remain unchanged. Loss of muscle mass underscores the need for nutritional strategies and long-term follow-up.

Key Words: Obesity; Steatotic liver disease; Bariatric surgery; Body composition; Hepatic steatosis

Core Tip: Six months after bariatric surgery, a significant reduction in body mass index, visceral fat, and metabolic parameters was observed, associated with an improvement in liver enzymes, especially alanine aminotransferase, suggesting regression of hepatic steatosis. Bioelectrical impedance analysis demonstrated a decrease in body fat, with relative preservation of muscle mass, although there is a risk of lean mass loss. Non-invasive indices of hepatic fibrosis, such as aspartate aminotransferase to platelet ratio index and fibrosis-4 index, did not show early changes, reinforcing the need for prolonged follow-up and individualized nutritional monitoring.

INTRODUCTION

Obesity is a multifactorial condition that affects millions of people worldwide and is one of the main risk factors for the development of various chronic diseases, including liver disorders[1]. Obesity, especially when associated with visceral fat, is strongly linked to liver diseases such as steatosis, which can progress to more severe forms, including metabolic dysfunction-associated steatohepatitis and cirrhosis[1,2]. These alterations are frequently associated with metabolic disturbances such as insulin resistance, dyslipidemia, and systemic inflammation, which exacerbate the patient’s clinical condition and increase the risk of hepatic impairment[3].

Obesity continues to rise at an alarming rate in Brazil. According to Vigitel 2023 data, 22.1% of the adult population already lives with obesity, and more than 56.8% are overweight[4]. Projections from the World Obesity Federation suggest that by 2030, over 68% of Brazilian adults will be overweight and 30% will have obesity[5]. Although interventions are primarily based on lifestyle changes, studies indicate low adherence due to factors such as lack of motivation, limited social support, and unfavorable socioeconomic conditions[6]. As an alternative treatment, glucagon-like peptide-1 (GLP-1) analogs, such as semaglutide, have demonstrated significant weight loss. However, their high cost—approximately United States $150 to $440 per month in Brazil—limits access, particularly in the public health system, and raises discussions about cost-effectiveness and equity in treatment[7].

Bariatric surgery is also an effective option for treating obesity and reversing or improving liver alterations such as steatosis, especially when other therapies fail to achieve adequate weight loss[8]. Recent studies highlight that bariatric surgery can reduce body mass index (BMI) and improve hepatic biochemical parameters, such as transaminases and glucose levels, in addition to promoting remission of conditions such as metabolic dysfunction-associated steatotic liver disease (MASLD)[9,10].

This surgical procedure may even be indicated for patients with compensated cirrhosis and obesity, particularly when metabolic control is difficult to achieve. It can improve glycemic control, reduce hepatic steatosis, decrease inflammation, and contribute to the regression of liver fibrosis[11]. Despite the high associated cost, the procedure is available through the Brazilian Unified Health System (SUS), expanding access for eligible patients[12].

The aim of this study was to investigate the effects of bariatric surgery on body composition, including visceral fat and body fat percentage, in patients with obesity associated with hepatic steatosis, as well as on biochemical and enzymatic parameters related to liver function, such as aspartate aminotransferase (AST) and alanine aminotransferase (ALT), and on the fibrosis-4 index (FIB-4) and AST to platelet ratio index (APRI) scores after 6 months of bariatric surgery.

MATERIALS AND METHODS

This was a retrospective cohort study that compared the preoperative and 6-month postoperative periods of bariatric surgery. The sample was selected by convenience, based on all patients treated at the service between July 2015 and July 2017 who met the inclusion criteria and had complete medical record data. Information was collected from the routine care protocol before and after surgery during outpatient follow-up.

The analyzed data included body composition, phase angle (PA), body resistance and reactance measured by electrical bioimpedance, as well as routine laboratory tests performed at the Center before and 6 months after the surgical procedure. During surgery, a liver biopsy was obtained. Patients were not resubmitted to biopsy after bariatric surgery, except in cases of surgical readmission that allowed sample collection, such as cholecystectomy, in accordance with the Center’s routine and ethical considerations.

Inclusion and exclusion criteria

Inclusion criteria: Adults aged 18 years or older, with a clinical diagnosis of obesity, who underwent routine biochemical evaluation at the center and electrical bioimpedance assessment in the preoperative and postoperative periods of bariatric surgery, and who were not enrolled in dietary programs at the time of the study, were included. All participants signed the informed consent form.

Exclusion criteria: Patients with physical limitations or amputations that prevented anthropometric assessment and body symmetry evaluation, those receiving enteral nutrition, those with chronic kidney failure, and those with chronic pancreatitis, pregnant women, people with pacemakers or cochlear implants, were excluded.

Patients with advanced-stage cancer, chronic diarrhea, symptomatic human immunodeficiency virus infection, or intestinal diseases associated with malabsorption syndromes were also excluded, as these conditions could interfere with the evaluated outcomes and compromise sample homogeneity.

Anthropometric data

Height was measured using a Tonelli wall-mounted stadiometer, model E150 A, with the patient in an upright position, feet together and head in the Frankfurt plane[13]. BMI was calculated using the equation that divides weight in kilograms by height in meters squared and was classified according to the World Health Organization criteria[14].

Bariatric surgery

Patients underwent bariatric surgery using the Roux-en-Y gastric bypass technique with intestinal bypass, after multidisciplinary evaluation and preparation by the service team. All patients met the criteria for bariatric surgery. The procedures were performed by four specialist surgeons from the same team, all equally trained and experienced in the technique.

Electrical bioimpedance

Body composition and weight data were measured using bioelectrical impedance analysis (BIA) with the calibrated InBody 770 device (Ottoboni), with an electrical current intensity of 80 μA and a frequency of 50/60 kHz, during the week prior to bariatric surgery. Patient preparation followed the guidelines of Kyle et al[15]. PA was obtained using resistance and reactance values according to the formula by Barbosa-Silva et al[16], calculated as PA = arctangent (Xc/R) × 180/3.1416. Reactance (Xc) and resistance (R) for total body (TB) were derived from segmental values obtained for the right leg (RL), trunk (TR), and right arm (RA), as reported in the BIA results sheet. The formulas used for Xc and R calculations were: XcTB = XcRA + XcRL + XcTR e RTB = raiz (ZRA)2 - (XcRA)2 + raiz (ZRL)2 - (XcRL)2 + raiz (ZTR)2 - (XcTR)216 - 17[17,18]. BIA was performed again on the same device 6 months after bariatric surgery as part of routine postoperative evaluation. For the BIA, the following preparation was carried out 24 hours before the exam: No alcohol consumption, no more than two episodes of loose stools, no sauna, sexual activity, or physical exercise. Fasting for 2 hours prior to the exam. Women during their menstrual period, understood as the period from 7 days before the first day of bleeding to 2 days after the last day of bleeding.

Hepatic scores: APRI and FIB-4

As part of the clinical and laboratory characterization of the participants, the noninvasive scores APRI and FIB-4 were used to estimate liver fibrosis. The data required for calculating these scores—serum AST, ALT, platelet count, and age—were obtained from routine laboratory tests performed before bariatric surgery and 6 months after the procedure. APRI was calculated using the formula: (AST/upper limit of normal AST) × 100/platelet count (10⁹/L). FIB-4 was calculated using the formula: (age × AST)/(platelets × √ALT). These scores are widely validated in clinical practice for estimating the degree of liver fibrosis, including in metabolic contexts such as MASLD and obesity, and are recommended by recent guidelines for noninvasive screening and monitoring of liver fibrosis[19,20].

Ethical procedures

The study was approved by the Research Ethics Committee of the Pontifical Catholic University of Rio Grande do Sul (No. 1.729.522), and received the Certificate of Ethical Appreciation (No. 58388816.3.0000.5336).

Participation in the study required volunteers to read and sign the Informed Consent Form. The research complies with the ethical guidelines established by Resolution No. 196/96 of the Brazilian National Health Council and follows the principles of the Declaration of Helsinki for research involving human subjects. Data management were conducted in accordance with the Brazilian General Data Protection Law (LGPD-Law No. 13.709/2018).

All researchers involved signed a Confidentiality Agreement submitted to the ethics committee, committing to maintain the confidentiality of all personal information collected throughout the study. Access to the final database was restricted exclusively to members of the research team.

Sample

The sample included all patients treated during the study period who met the inclusion criteria and underwent electrical bioimpedance as well as biochemical analyses in both the preoperative and postoperative periods. Initially, the sample consisted of 153 patients; 61 of these were excluded from the study due to incomplete medical record data or failure to complete the 6-month postoperative follow-up examinations.

Statistical analyses

Quantitative variables are described as the mean and standard deviation or as the median and interquartile range. Data distribution was assessed using the Kolmogorov-Smirnov test. Categorical variables were described as absolute and relative frequencies.

To compare pre- and post-operative means, the paired Student’s t-test was applied. In cases of non-normal distribution, the Wilcoxon test was used. This same test was also applied to evaluate ordinal variables.

The significance level adopted was 5% (P < 0.05), and analyses were performed using SPSS software, version 21.0. The project was developed in accordance with Resolution 466/2012, which regulates research involving human subjects.

RESULTS

The convenience sample of 91 patients consisted of 80% women, with a mean age of 36.4 years, characterizing a young population. All patients underwent liver biopsy during the surgical procedure. As shown in Table 1, all patients presented steatosis at varying degrees, and only 16.48% exhibited mild fibrosis.

Table 1 Sample characteristics in the preoperative and postoperative periods, mean ± SD.

Variables	Preoperative, n = 91	Postoperative, n = 91	Δ	P value
Age	36.385 ± 9.54	36.385 + 9.54	0	1
APRI	0.309 ± 0.269	0.285 ± 0.14	0	0.454
FIB4	0.619 ± 0.329	0.667 ± 0.314	-0.024	0.320
BMI (kg/m2)	42.989 ± 6.043	30.86 ± 4.783	0.048	< 0.001b
ALT	27.911 ± 20.2	23.471 + 10.496	-12.13	0.004b
AST	36.457 ± 27.807	29.11 + 17.487	-7.347	0.134
Platelets	287.725 ± 67.307	255.318 ± 56.218	-4.44	0.001
Hemoglobin	13.739 ± 1.384	13.349 + 1.667	-32.407	0.857
Fasting glucose	98.208 ± 20.305	84.919 + 13.194	0.802	< 0.001b
Triglycerides	159.043 ± 77.76	91.334 + 28.751	-13.289	0.038a
Total cholesterol	197.773 ± 36.307	156.32 + 30.516	-70.106	0.513
HDL cholesterol	46.975 ± 12.984	48.884 + 13.265	-41.985	0.069
Creatinine	0.863 + 0.698	0.818 + 0.263	1.909	0.018a
Uric acid	6.807 ± 8.195	4.739 + 3.248	0.045	0.201
Vitamin D	24.298 ± 9.154	35.756 + 50.159	-2.069	0.004b
Vitamin B12	454.135 ± 177.37	541.359 + 299.518	11.458	0.003b
Ferritin	208.871 ± 221.093	143.534 + 134.435	87.224	0.463
Albumin	4.26 ± 0.327	4.121 + 0.596	-65.337	0.982

^aP < 0.05.

^bP < 0.01.

Paired Student’s t-test. ALT: Alanine aminotransferase; APRI: Aspartate aminotransferase to platelet ratio index; AST: Aspartate aminotransferase; BMI: Body mass index; FIB-4: Fibrosis-4 index; HDL: High-density lipoprotein.

In the sample characterization (Table 1), comparing pre- and post-operative data, we observed significant differences in BMI, ALT, platelets, glucose, triglycerides, creatinine, vitamin D, and vitamin B12, as well as a trend toward significance for high-density lipoprotein. Albumin levels did not change. The APRI and FIB-4 scores were not significant.

Due to procedural limitations and to ensure patient safety, only the preoperative biopsy was available. It was observed that all patients presented some degree of steatosis, with 39 individuals (42.86%) showing mild steatosis, 20 (20.08%) moderate, 22 (24.18%) marked, and 9 (9.89%) massive steatosis. Additionally, 15 patients (16.48%) presented evidence of fibrosis.

In Table 2, regarding the categorical BIA data in the pre- and post-operative periods, statistically significant differences were observed in all analyzed variables, with notable improvement in the number of patients who reached normal ranges for total body water (TBW) and proteins, nearly half of the sample.

Table 2 Preoperative and postoperative bioelectrical impedance analysis data—categorical variables, n (%).

Categorical variables	Preoperative, n = 91	Postoperative, n = 91	Δ	P value
REF total body water				< 0.001b
Below	-	-	0
Normal	4 (4.4)	42 (46.15)	38
Above	87 (95.6)	49 (53.85)	-38
REF proteins				< 0.001b
Below	-	-	0
Normal	6 (6.59)	46 (50.55)	40
Above	85 (93.41)	45 (49.45)	-40
REF minerals				< 0.001b
Below	-	-	0
Normal	6 (6.59)	16 (17.58)	10
Above	85 (93.41)	75 (82.42)	-10
REF fat mass				< 0.001b
Below	-	-	0
Normal	1 (1.1)	7 (7.69)	6
Above	90 (98.9)	84 (92.31)	-6
REF skeletal muscle mass				< 0.001b
Below	-	1 (0.011)	1
Normal	4 (4.4)	41 (45.05)	37
Above	87 (95.6)	49 (53.85)	-38
REF body fat percentage				< 0.001b
Below	-	-	0
Normal	-	4 (4.4)	4
Above	91 (100)	87 (95.6)	-4
REF intracellular water				< 0.001b
Below	-	1 (1.1)	1
Normal	6 (6.59)	45 (49.45)	39
Above	85 (93.41)	42 (46.15)	-43
REF extracellular water				< 0.001b
Below	-	-	0
Normal	6 (6.59)	31 (34.07)	25
Above	85 (93.41)	57 (62.64)	-28
REF body cell mass				< 0.001b
Below	-	1 (1.1)	1
Normal	7 (7.69)	40 (43.96)	33
Above	84 (92.31)	47 (51.65)	-37

^bP < 0.01.

χ² test. REF: Reference values.

Table 3 presents the continuous BIA data of patients in the pre- and post-operative periods. We observed a significant reduction in body fat percentage and visceral fat area in the postoperative assessment, as well as a trend toward decreased fat mass. The BIA PA, in this evaluation, did not show significance for fat mass or visceral fat volume in the postoperative period.

Table 3 Preoperative and postoperative bioelectrical impedance analysis data—continuous variables, mean ± SD.

Variables	Preoperative, n = 91	Postoperative, n = 91	Δ	P value
Total body water (L)	43.47 ± 9.194	38.686 + 8.244	-4.785	0.334
Proteins	11.632 ± 2.426	10.216 + 2.17	-1.415	0.321
Minerals	3.851 ± 0.841	3.807 + 0.822	-0.043	0.851
Fat mass (kg)	59.362 ± 14.157	32.151 + 10.914	-27.211	0.09
Skeletal muscle mass (kg)	33.112 ± 7.328	28.719 + 6.457	-4.393	0.229
Body fat percentage	50.036 ± 4.117	37.392 + 7.33	-12.644	< 0.001b
Intracellular water (L)	26.893 ± 5.509	23.7 + 4.757	-3.193	0.211
Extracellular water (L)	16.382 ± 3.629	14.922 + 3.167	-1.461	0.262
Basal metabolic rate (kcal)	1643.802 ± 268.411	1508.703 + 242.396	-135.099	0.36
Visceral fat area (cm2)	243.304 ± 29.066	152.459 + 50.785	-90.845	< 0.001b
Body cell mass (kg)	38.56 ± 8.04	33.781 + 7.021	-4.78	0.229
Whole-body phase angle	5.895 ± 0.521	4.977 + 0.543	-0.917	0.982
Right arm phase angle	5.534 ± 0.571	4.7 + 0.571	-0.834	0.756
Left arm phase angle	5.384 ± 0.588	4.51 + 0.532	-0.873	0.507
Trunk phase angle	7.768 ± 1.211	6.586 + 1.279	-1.182	0.463
Right leg phase angle	6.254 ± 0.579	5.264 + 0.64	-0.99	0.813
Left leg phase angle	6.178 ± 0.625	5.203 + 0.68	-0.975	0.939

^bP < 0.01.

Paired Student’s t-test. BMR: Basal metabolic rate; LL: Lower limb; PA: Phase angle; SMM: Skeletal muscle mass; UA: Upper limb.

DISCUSSION

In the present study, evaluating patients 6 months after bariatric surgery, the majority were female, with a mean age of 36.385 ± 9.54 years and a BMI of 42.989 ± 6.04, all presenting steatosis and a mild elevation of ALT. After gastrectomy, we observed a decrease in BMI to 30.860 ± 4.78 (P < 0.001), ALT (P < 0.004), fasting glucose (P < 0.001), platelets (P < 0.001), triglycerides (P < 0.038), creatinine (P < 0.018), vitamin D (P < 0.004), and vitamin B12 (P < 0.003). The APRI and FIB-4 scores were not significant.

These findings are similar to the results reported by Bezerra et al[21], in which 63.3% of the sample were women, the mean age was 41 years, and significant changes in body composition were observed.

The study by Ciardullo et al[22]. indicates that, despite female predominance, post-bariatric weight loss is significant but greater in men. This may be attributed to higher muscle mass, metabolic rate, and hormonal influence, particularly testosterone[23], highlighting the importance of sex as a variable in surgical response.

Another relevant finding was the reduction in ALT levels, which is associated with hepatocellular injury and may suggest improvement in hepatic inflammation. A 2020 observational cohort study evaluated changes in liver enzymes and predictive scores for hepatic steatosis (fatty liver index [FLI]) and liver fibrosis (BARD) 1 year after the procedure. The results showed a significant reduction in liver enzyme levels, ALT and AST, as well as improvements in the FLI and BARD scores, suggesting a decrease in hepatic fat and fibrosis[24].

A national cohort study conducted by Seyedi et al[25]. evaluated the impact of bariatric surgery on liver fibrosis indices in patients with type 2 diabetes and revealed reductions in ALT and AST enzymes from 6 months onward, indicating a significant improvement in hepatic enzyme profile.

These changes occur due to substantial weight loss, reduction of visceral fat, decreased hepatic lipid accumulation, and improved metabolism, which reduce hepatic inflammation and lower enzymes released by damaged hepatocytes[26]. Furthermore, surgery improves insulin resistance, contributing to the reduction of hepatic steatosis and prevention of fibrosis progression[26,27]. The study by Seyedi et al[25], cited above, also identified reductions in triglycerides and fasting glucose, corroborating the findings in our sample.

These effects are explained by significant weight loss, which improves lipid metabolism and insulin resistance[28]. Additionally, potential changes in gut microbiota and alterations in intestinal hormone secretion, such as GLP-1, favor better glycemic and lipid control. Finally, improved insulin sensitivity after surgery reduces hepatic glucose and triglyceride production[28,29].

All patients presented steatosis of varying degrees: 42.6% mild, 47.14% moderate to marked, 9.89% massive, and 16.48% mild fibrosis. For ethical reasons, routine postoperative liver biopsy is prohibited and is performed only if the patient requires a laparotomy due to an intercurrent event (appendectomy, cholecystectomy, acute abdomen, etc.). A previous study[17] by the same group, involving bariatric surgery in 379 patients following the same protocol, demonstrated that hepatic histological changes were similar to those found in our 91 patients, and 33 postoperative liver biopsies were performed up to 2 years after surgery. Findings from these second biopsies showed reductions in steatosis, inflammation, and hepatocellular ballooning, evidencing the positive impact of bariatric surgery.

One method for assessing liver fibrosis is through elastography. This is a promising approach for monitoring the progression of liver fibrosis and can be used in the postoperative period after bariatric surgery, allowing for noninvasive evaluation of regression or progression of fibrotic tissue over time[30,31]. Therefore, it is suggested that future studies incorporate sequential assessments at regular intervals to better understand the impact of surgery on liver fibrosis and to guide individualized interventions[30].

The APRI and FIB-4 scores did not show significant results, likely due to the short duration of the analysis, as fibrosis usually regresses more slowly, around 12 months post-surgery, with continued reductions up to 5 years[32]. Supporting this finding, a 2024 meta-analysis showed that while APRI demonstrated significant improvement between 3 months and 36 months, FIB-4 may not show changes in the short term and is more sensitive only in longer follow-ups[32]. The absence of a decrease in APRI and FIB-4 scores at 6 months is consistent with the literature, reflecting the delayed nature of liver fibrosis regression.

Additionally, although APRI and FIB-4 were used as indicators of hepatic improvement, the study sample presented predominantly low baseline fibrosis levels. This characteristic may have limited the sensitivity and differentiating capacity of these scores to detect clinically meaningful changes over time. Therefore, the absence of a decrease in APRI and FIB-4 scores at 6 months is consistent with the literature and should be interpreted with caution, as low baseline fibrosis may have attenuated the detection of significant variations in these markers.

Contrary to the study by Seyedi et al[25], which did not find significant changes in serum creatinine, our data showed a reduction. Although this finding was significant, creatinine values remained within the normal range both preoperatively and postoperatively. However, the reduction in body fat caused by bariatric surgery decreases the renal load, which may lead to more efficient kidney function and lower creatinine levels. Additionally, improvements in blood pressure and insulin resistance are factors associated with better renal function[33]. These findings are reinforced by the study of Huang et al[34], which observed improved glomerular filtration rate and decreased creatinine after bariatric surgery.

The increase in vitamin D and vitamin B12 levels postoperatively is associated with supplementation, which is essential after bariatric surgery due to malabsorption caused by anatomical alterations of the gastrointestinal tract[35,36]. We also observed reductions in proteins and minerals via bioimpedance, attributed to gastrectomy. Supplementation is fundamental to prevent deficiencies and maintain bone and neurological health[36].

Continuous data related to BIA assessment (Table 3) showed a significant change in body fat percentage (P < 0.001), visceral fat area (P < 0.001), and a trend toward decreased fat mass (P < 0.09). There were no changes in proteins, minerals, or skeletal muscle mass.

The study by Ferber et al[37] presented results similar to ours regarding body composition, with reductions in body fat, body fat percentage, and fat-free mass (FFM), and consequently, muscle mass, at 6 months postoperatively. The decrease in muscle mass and other lean tissues is a crucial consideration in evaluating postoperative complications, resulting from malabsorption, acute malnutrition, and protein catabolism induced during the initial weight-loss phase after surgery[38].

The benefits of weight loss from bariatric surgery outweigh those resulting from muscle mass loss, according to Nuijten et al[38], even considering its detrimental effects on metabolism, thermoregulation, bone strength, functional capacity, glycogen, fat and protein storage. Muscle mass loss can lead to reduced basal metabolism, functional impairment, decreased quality of life[39,40], and imbalance in energy regulation, increasing appetite, which negatively impacts long-term procedural success and may lead to weight regain[41,42].

Sarcopenic obesity, defined as obesity associated with loss of muscle mass and function, can occur before or after bariatric surgery[42,43]. Gastrectomy induces approximately 8 kg of muscle mass loss in 1 year, with 55% occurring in the first 3 months[44,45]. In the present study, muscle mass loss was observed, although not statistically significant. Therefore, nutritional interventions and resistance training are essential to minimize this loss[43], whose pathophysiology and treatment are not yet fully understood[44].

Preservation of lean mass after bariatric surgery is critical for maintaining metabolism and muscle function. Combined resistance and aerobic training programs, initiated early, have been shown to be effective in retaining FFM[45,46]. Thus, integrating individualized nutrition and structured physical activity represents an effective strategy to optimize postoperative metabolic outcomes.

Despite these critical considerations, bariatric surgery provides undeniable weight loss benefits and promotes improvements in body composition, preventing obesity-related health risks. Ferber et al[37] reported a reduction in fat mass from an initial mean of 48.33 kg to 41.69 kg at 6 months, highlighting the procedure’s effectiveness, consistent with our findings. In our study, we observed a significant reduction in visceral fat area, which is associated with type 2 diabetes, systemic arterial hypertension, cardiovascular disease, and liver disease related to steatosis, as also reported by Cantini et al[47].

Visceral fat loss is associated with a decrease in hepatic fat, reduced transaminase levels (AST and ALT), and decreased hepatic inflammation[48]. These effects are particularly important for patients with MASLD, a condition frequently related to visceral fat accumulation, where bariatric surgery promotes weight loss, reduces steatosis, lowers liver enzyme levels, and decreases the risk of progression to severe liver disease such as fibrosis and cirrhosis[49,50].

The reduction in visceral fat, total body fat, as well as BMI, plays a central role in improving hepatic steatosis by decreasing hepatic lipid accumulation and enhancing insulin sensitivity. Recent studies have shown that visceral fat reduction is strongly associated with steatosis regression, a condition observed in all patients in this study, and also contributes to the progressive improvement of hepatic fibrosis indices in the long term[51]. Furthermore, changes in body composition, particularly reductions in body fat percentage, predict improvements in steatosis more accurately than BMI alone[52].

Analyzing Table 2, categorical BIA data, we observed that all parameters were significant. Regarding body cell mass measured by BIA which determines the amount of living cells in the body, excluding non-living components such as bones, fat, and extracellular water[53], our study showed a reduction. However, individuals shifted into the normal range after surgery, corroborating the study by Nuijten et al[38], which demonstrated a reduction in body cell mass after gastrectomy, particularly significant during the first 6 months postoperatively.

This parameter reflects cells involved in active metabolic processes, including muscle cells and cells of organs and other tissues. Body cell mass is an important indicator of metabolic health, as reduced levels may indicate risk for conditions such as sarcopenia and other metabolic disorders. Moreover, the relationship between TBW and body cell mass allows BIA to be used as a tool to detect imbalances in hydration status and essential nutritional deficiencies, which are fundamental for evaluating overall patient health[54].

After bariatric surgery, TBW decreases, as observed by BIA. Postoperatively, there is a reduction in lean mass and intracellular water, an important component of TBW. BIA estimates these parameters through electrical resistance, differentiating intra- and extra-cellular water[55].

Studies have shown that in the postoperative period of bariatric surgery, there is a reduction in TBW volume, especially during the first weeks; our study also observed this outcome[55,56]. This reduction can be explained by factors such as decreased fluid intake, metabolic changes, and accelerated weight loss. Such a decrease can affect the body’s water balance and contribute to symptoms such as dehydration and fatigue, highlighting the importance of monitoring these parameters to adjust hydration and nutrition[57,58].

CONCLUSION

Studies on body composition, biochemical, and histological parameters after bariatric surgery present methodological limitations, such as small sample sizes, short follow-up periods, and poorly controlled variables. These factors hinder the interpretation of long-term effects and underscore the need for more robust longitudinal studies.

Also, given the exploratory nature of this analysis and the paired study design, no formal correction for multiple comparisons was applied; consequently, there is a potential risk of type I error, particularly for secondary endpoints.

In conclusion, bariatric surgery demonstrated effectiveness at 6 months in reducing body weight, improving body composition in terms of total and visceral fat, and enhancing biochemical and enzymatic parameters, including ALT and AST, indicating potential benefits for metabolic health.

Although the surgical procedure offers clear benefits, the preservation of muscle and body cell mass remains a significant challenge, given its impact on recovery and long-term quality of life. Measures such as adequate protein intake combined with resistance and aerobic exercise should be implemented postoperatively to promote this preservation.

More robust and longer-term studies are necessary to accurately evaluate the effects of bariatric surgery on liver function. The incorporation of sequential elastography would allow noninvasive monitoring of fibrosis and steatosis progression over time, while targeted nutritional and therapeutic strategies could be developed to optimize postoperative metabolic and hepatic outcomes.