Key words bariatric surgery - meta-analysis - leptin - adiponectin - resistin
Introduction
Obesity, which is defined as excessive expansion of white adipose tissue, is a global
health problem with reported prevalence of more than 1.9 billion around the world
[1 ]. It is associated with a range of
health-related problems and major chronic diseases including cancer, cardiovascular
diseases (CVD), and diabetes mellitus (DM) [2 ]
[3 ]
[4 ]. There is thus an urgent need for patients
with obesity to get rid of their excess fat. Many conservative therapies such as
restricted diet take time and do not result in sustained weight loss [5 ], whereas bariatric surgery appears to have a
better outcome [6 ]
[7 ]. Food intake is reduced following
bariatric surgery as a consequence of either reducing the size of stomach through
insertion of a gastric band, or the removal of a part of the stomach or reducing the
length of the small intestine. Long-term studies indicate this type of surgery, is
not effective for weight loss [5 ], but also
ameliorate a variety of obesity-related diseases such as DM and CVD [8 ]. However, some adverse effects may be
expected due to the magnitude of the procedure [9 ]. Moreover, whether it also has further benefits due to an improved
profile of circulating adipokines remains to be fully clarified.
Adipose tissue is a loose connective tissue, which is mainly composed of adipocytes.
It acts as an energy storing for lipids and is recognized as the biggest endocrine
organ of the human body, secreting several soluble factors, known as adipokines
[10 ]. These are critical regulators of
systemic lipid and glucose homeostasis, although most are associated with
obesity-related health problems such as insulin resistance, beta-cell dysfunction,
endothelial dysfunction, and atherosclerosis [11 ]
[12 ]
[13 ]
[14 ]. Although leptin can regulate energy
balance by inhibiting hunger, obesity results in a loss of sensitivity [15 ]. Adiponectin is a protein hormone with an
anti-inflammatory role that can modulate glucose and lipid homeostasis [16 ]. Chemerin, is a chemoattractant protein,
that is necessary for adipogenesis, which when elevated in adipose tissue may be a
marker for the onset of DM [17 ]. Visfatin is
an enzyme that activates insulin and has insulin-mimetic effects [18 ], whereas plasminogen activator inhibitor-1
(PAI-1), is the primary inhibitor of tissue- and urokinase-type plasminogen
activators, and considered to be a critical regulator of the fibrinolytic system
[19 ]. Finally, resistin promotes hepatic
production of low density lipoproteins (LDL), which degrades LDL receptors [20 ].
Weight loss after bariatric surgery is mainly due to the loss of visceral fat [21 ], but whether the secretion of adipokines is
then modulated remains to be fully established as the response varies [22 ]
[23 ]
[24 ] and is not always significant [25 ]
[26 ]
[27 ]
[28 ]
[29 ]
[30 ]. We, therefore, conducted a meta-analysis
and systematic review to investigate the effect of different types of bariatric
surgeries on these adipokines.
Materials and Methods
This meta-analysis and systematic review was performed according to the Preferred
Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) [31 ].
Search strategy
PubMed/Medline and Scopus were searched from inception to January 2019
using the following terms in titles and abstracts: ((leptin
[Title/Abstract]) OR (adiponectin [Title/Abstract]) OR
(PAI-1 [Title/Abstract]) OR (“Plasminogen
activator inhibitor-1 ” [Title/Abstract]) OR
(visfatin [Title/Abstract]) OR (“pre-B cell
colony-enhancing factor-1 ” [Title/Abstract]) OR
(PBEF [Title/Abstract]) OR (“nicotinamide
phosphoribosyltransferase ” [Title/Abstract]) OR
(Nampt [Title/Abstract]) OR (Chemerin
[Title/Abstract]) OR (re sistin [Title/Abstract]) OR
(“adipocyte secreted factor ”
[Title/Abstract]) OR (ADSF [Title/Abstract]) OR
(FIZZ-3 [Title/Abstract])) AND ((“Bariatric
Surgery ” [Mesh]) OR (“Gastric Bypass ”
[Title/Abstract]) OR (“Gastrectomy ”
[Title/Abstract]) OR (“Bariatric Surgery ”
[Title/Abstract]) OR (“Biliopancreatic Diversion ”
[Title/Abstract]) OR (Gastroplasty [Title/Abstract]) OR
(bariatric [Title/Abstract]) OR (Roux-en-Y
[Title/Abstract]) OR (RYGB [Title/Abstract]) OR
(“Sleeve gastrectomy ” [Title/Abstract]) OR
(“Gastric sleeve ” [Title/Abstract]) OR
(“gastric band ” [Title/Abstract]) OR
(Lap-Band [Title/Abstract]) OR (“duodenal
switch ” [Title/Abstract])). As we did not want to miss
any relevant articles, all the reference list of eligible articles, related
reviews, and meta-analyses were hand-searched.
Eligibility criteria
Title and abstract of all retrieved articles in the initial search were screened
separately by two different reviewers. Studies were included if they met the
following criteria (1) reported baseline BMI and at least one of the following
measures; leptin, adiponectin, PAI-1, visfatin, chemerin, and resistin before
and after surgical intervention, (2) performed one of the common bariatric
surgeries [Roux-en-Y gastric bypass (RYGB); SG, gastric bypass (GBP); vertical
banded gastroplasty (VBG); GB, Biliopancreatic diversion (BPD)], and (3)
bariatric surgery were performed only for treatment of obesity and not any other
reason. Articles were excluded if they had the following exclusion criteria: (1)
the reason of surgery was not obesity, (2) had insufficient data for the
outcomes of interest in individuals, and (4) experimental and animal studies.
All editorials, reviews, letters to editors, conference papers, animal studies,
and molecular studies were excluded.
Data extraction
Two independent researchers (MAE and GH) did the study selection, whereas to
resolve any controversies, a chief investigator (SA) was present. The following
data were acquired from each study; first author’s name; year of
publication; study location; study duration; number of participant’s,
participant’s age and gender; study design; weight and BMI before and
after intervention; participant’s health status; mean and SD of serum or
plasma levels of leptin, adiponectin, PAI-1, visfatin, chemerin, and resistin.
Also if all individuals just had the same disease, it was reported ([Fig. 1 ]
[2 ]).
Fig. 1 Forest plot presenting mean difference (MD) and
95% confidence intervals for the impact of bariatric surgery on
a adiponectin and b leptin. Results from
Hedges’ g analysis.
Fig. 2 Forest plot presenting mean difference (MD) and
95% confidence intervals for the impact of bariatric surgery on
a visfatin (ng/ml), b plasminogen activator
inhibitor-1 (ng/ml), c resistin (ng/ml), and
d chemerin (ng/ml).
Assessment of study quality
Two authors independently assessed the quality of included studies by the
Newcastle-Ottawa Quality Assessment Scale (NOS). This scale comprising of three
quality factors: selection (maximum 4 stars), comparability (maximum 2 stars),
and outcome (maximum 3 stars). A maximum of 9 stars represents the highest
quality. A total score of 7 or more was considered to indicate high-quality
studies [32 ]
[33 ].
Statistical analysis
Mean difference was used as the effect size and a random effects model was
utilized for the meta-analysis [34 ]. Using
random-effects model, effect sizes were acquired as the weighted mean difference
(WMD) and 95% CI by DerSimonian–Laird method. When reported
variable could not be pooled, Hodges’s adjusted g was used to calculate
overall estimate of effect size. A test for heterogeneity was performed (using Q
statistic and I2 ) [35 ]. The
subgroup analysis (Table 2S ) was conducted to find out possible sources
of heterogeneity among included studies. Meta-regression analysis was performed
to investigate whether participant baseline BMI and also duration of follow up
could explain the heterogeneity across studies and also affect measured effect
size. Publication bias was investigated by visual inspection of the funnel plot
as well as by using the Egger’s regression method. In case of
publication, bias trim and fill analysis were performed. This specific analysis
was conducted for evaluating the possible effect of publication bias on overall
estimate of effect size based on possible relevant unpublished studies [36 ]. We used the sensitivity analysis to
assess the effect of each study on the overall effect size by removing each
individual study in turn. All statistical analyses were carried out using Stata
MP V.14.0 (StataCorp, College Station, Texas, USA).
Results
Study selection
PRISMA flow diagram of the search process is depicted in (Fig. 1S )
(Supporting Information). A total of 2071 papers were found. After removing
duplicates, 1706 abstracts were selected for a more detailed review. Following
screening based on the title and abstract, 1599 articles were excluded: 1) 1493
unrelated topics, 2) 28 animal studies, 3) 78 letters, reviews, and book
sections. One hundred and seven citations remained after screening for title and
abstracts. After full-text evaluation a further 22 studies were also excluded:
1) combination with other treatments (n= 3), and 2) with not
enough information (n= 19). Finally, 83 prospective and 2
retrospective studies remained for the systematic review (Table 1S )
(Supporting Information).
Findings from systematic review
Characteristics of eligible studies are summarized in (Table 1S ), with a
sample size of between 5 and 180 participants who underwent bariatric surgery
(total sample size of studies; n=3512).
Sixty-one studies reported leptin [22 ]
[23 ]
[25 ]
[27 ]
[28 ]
[30 ]
[37 ]
[38 ]
[39 ]
[40 ]
[41 ]
[42 ]
[43 ]
[44 ]
[45 ]
[46 ]
[47 ]
[48 ]
[49 ]
[50 ]
[51 ]
[52 ]
[53 ]
[54 ]
[55 ]
[56 ]
[57 ]
[58 ]
[59 ]
[60 ]
[61 ]
[62 ]
[63 ]
[64 ]
[65 ]
[66 ]
[67 ]
[68 ]
[69 ]
[70 ]
[71 ]
[72 ]
[73 ]
[74 ]
[75 ]
[76 ]
[77 ]
[78 ]
[79 ]
[80 ]
[81 ]
[82 ]
[83 ]
[84 ]
[85 ]
[86 ]
[87 ]
[88 ]
[89 ]
[90 ]
[91 ], 40 adiponectin [22 ]
[23 ]
[26 ]
[28 ]
[29 ]
[30 ]
[40 ]
[43 ]
[46 ]
[47 ]
[49 ]
[54 ]
[56 ]
[57 ]
[61 ]
[62 ]
[67 ]
[72 ]
[73 ]
[74 ]
[78 ]
[79 ]
[89 ]
[90 ]
[91 ]
[92 ]
[93 ]
[94 ]
[95 ]
[96 ]
[97 ]
[98 ]
[99 ]
[100 ]
[101 ]
[102 ]
[103 ]
[104 ]
[105 ]
[106 ], 11 resistin [23 ]
[24 ]
[27 ]
[30 ]
[62 ]
[74 ]
[78 ]
[82 ]
[91 ]
[105 ]
[107 ], 7 visfatin [24 ]
[25 ]
[57 ]
[61 ]
[100 ]
[108 ]
[109 ], PAL-1 [27 ]
[65 ]
[89 ]
[110 ]
[111 ], and 3 chemerin [24 ]
[88 ]
[112 ]. Across the included studies 8 were
performed on patients with DM [30 ]
[47 ]
[65 ]
[90 ]
[91 ]
[99 ]
[105 ]
[111 ], one study was on the metabolic
syndrome [73 ], one on obstructive sleep
apnea [106 ], another study stratified
subjects based on different polymorphisms of tumor necrosis
factor-α-G308A genotype [107 ] and
other studies were carried out just on participants with obesity [22 ]
[23 ]
[24 ]
[25 ]
[26 ]
[27 ]
[28 ]
[29 ]
[37 ]
[38 ]
[39 ]
[40 ]
[41 ]
[42 ]
[43 ]
[44 ]
[45 ]
[46 ]
[48 ]
[49 ]
[50 ]
[51 ]
[52 ]
[53 ]
[54 ]
[55 ]
[56 ]
[57 ]
[58 ]
[59 ]
[60 ]
[61 ]
[62 ]
[63 ]
[64 ]
[66 ]
[67 ]
[68 ]
[69 ]
[70 ]
[71 ]
[72 ]
[74 ]
[75 ]
[76 ]
[77 ]
[78 ]
[79 ]
[80 ]
[81 ]
[82 ]
[83 ]
[84 ]
[85 ]
[86 ]
[87 ]
[88 ]
[89 ]
[92 ]
[93 ]
[94 ]
[95 ]
[96 ]
[97 ]
[98 ]
[100 ]
[101 ]
[102 ]
[103 ]
[104 ]
[108 ]
[109 ]
[110 ]
[112 ].
Across the included studies 26 were on patients with a Roux-en-Y gastric bypass
(RYGB) [29 ]
[30 ]
[42 ]
[45 ]
[46 ]
[47 ]
[48 ]
[51 ]
[63 ]
[67 ]
[68 ]
[69 ]
[73 ]
[74 ]
[76 ]
[79 ]
[80 ]
[86 ]
[87 ]
[91 ]
[95 ]
[99 ]
[104 ]
[105 ]
[110 ]
[111 ], 18 after various forms of surgery
[22 ]
[43 ]
[54 ]
[56 ]
[57 ]
[72 ]
[78 ]
[81 ]
[82 ]
[83 ]
[88 ]
[89 ]
[92 ]
[100 ]
[103 ]
[106 ]
[108 ]
[109 ], 14 bilio-pancreatic diversion (BPD)
[25 ]
[28 ]
[37 ]
[38 ]
[39 ]
[40 ]
[41 ]
[54 ]
[55 ]
[58 ]
[77 ]
[97 ]
[107 ]
[112 ], 8 gastric bypass (GBP) [23 ]
[53 ]
[54 ]
[93 ]
[94 ]
[96 ]
[98 ]
[101 ], 6 adjustable gastric banding (AGB)
[24 ]
[52 ]
[64 ]
[69 ]
[70 ]
[90 ], 6 gastric banding (GB) [26 ]
[61 ]
[65 ]
[66 ]
[71 ]
[104 ], 5 laparoscopic sleeve gastrectomy
(LSG) [27 ]
[44 ]
[49 ]
[62 ]
[85 ], 4 after vertical banded gastroplasty
(VBG) [54 ]
[60 ]
[84 ]
[102 ], 2 sleeve gastrectomy (SG) [59 ]
[94 ], 1 laparoscopic gastric banding (LGB)
[50 ], and 1 laparoscopic minigastric
bypass surgery (LMGBP) [75 ].
In addition, studies were performed in subjects with different baseline BMIs, 7
were in subjects between 30–39.9 kg/m2
[29 ]
[40 ]
[72 ]
[75 ]
[94 ]
[99 ]
[111 ], 21 in subjects between
40–44.9 kg/m2
[26 ]
[27 ]
[38 ]
[45 ]
[49 ]
[50 ]
[55 ]
[56 ]
[62 ]
[67 ]
[69 ]
[71 ]
[77 ]
[78 ]
[80 ]
[85 ]
[89 ]
[94 ]
[104 ]
[105 ]
[106 ], 44 in subjects between
45–49.9 kg/m2
[23 ]
[24 ]
[37 ]
[39 ]
[41 ]
[42 ]
[43 ]
[44 ]
[46 ]
[47 ]
[48 ]
[51 ]
[52 ]
[54 ]
[58 ]
[59 ]
[60 ]
[61 ]
[64 ]
[66 ]
[68 ]
[69 ]
[70 ]
[73 ]
[74 ]
[81 ]
[82 ]
[83 ]
[84 ]
[87 ]
[88 ]
[90 ]
[92 ]
[93 ]
[98 ]
[100 ]
[101 ]
[102 ]
[103 ]
[106 ]
[107 ]
[108 ]
[110 ]
[112 ], and 17 studies in subjects over
than 50 kg/m2
[ 22 ]
[28 ]
[53 ]
[57 ]
[76 ]
[86 ]
[91 ]
[95 ]
[96 ]
[97 ]
[99 ]
[109 ], whilst 4 studies did not report BMI
[30 ]
[54 ]
[65 ]
[79 ].
Twenty studies were on females only [25 ]
[26 ]
[45 ]
[51 ]
[52 ]
[54 ]
[55 ]
[60 ]
[62 ]
[71 ]
[73 ]
[77 ]
[78 ]
[94 ]
[96 ]
[98 ]
[101 ]
[102 ]
[108 ]
[109 ] and 2 on males only [41 ]
[81 ] and the rest included studies
conducted on both genders [22 ]
[23 ]
[24 ]
[27 ]
[28 ]
[29 ]
[30 ]
[37 ]
[38 ]
[39 ]
[40 ]
[42 ]
[43 ]
[44 ]
[46 ]
[47 ]
[48 ]
[49 ]
[50 ]
[53 ]
[56 ]
[57 ]
[58 ]
[59 ]
[61 ]
[63 ]
[64 ]
[65 ]
[66 ]
[67 ]
[68 ]
[69 ]
[70 ]
[72 ]
[74 ]
[75 ]
[76 ]
[79 ]
[80 ]
[82 ]
[83 ]
[84 ]
[85 ]
[86 ]
[87 ]
[88 ]
[89 ]
[90 ]
[91 ]
[92 ]
[93 ]
[95 ]
[97 ]
[99 ]
[100 ]
[103 ]
[104 ]
[105 ]
[106 ]
[107 ]
[110 ]
[111 ]
[112 ].
Meta-analysis results
Effect of bariatric surgery on circulating adiponectin
Fifty-four prospective studies including a total of 1862 participants
reported circulating adiponectin after bariatric surgery. Overall, combined
results showed that circulating adiponectin increased following bariatric
surgery (Hedges’ g=1.401, 95% CI: 1.101, 1.701,
p<0.001) ([Fig. 1a ]). Due to
a significant heterogeneity between studies
(I2= 99.3%, p<0.001), subgroup analyses
were performed based on gender (female/both), type of surgery
(RYGB/GB/GBP/BPD/miscellaneous/various),
baseline BMI
(˂ 45 kg/m2 /≥45 kg/m2 ),
follow-up period (≤ 3 months/6–11
months/12 months/˃ 12 months). This revealed that
the effect of bariatric surgery on adiponectin remained significant in all
subgroups except for GB type of surgery, although a lack of eligible studies
in this type of surgery must be considered before making any conclusion.
Effect of bariatric surgery on circulating leptin
Seventy prospective and retrospective studies including a total of 2751
participants reported leptin as an outcome measure. Pooled effect size
showed that circulating leptin decreased significantly following bariatric
surgery (Hedges’ g=–2.178, 95% CI:
–2.433, –1.923, p<0.001) ([Fig. 1b ]). There was significant
heterogeneity among included studies (I2 =92.3%,
p<0.001). Subgroup analysis also was performed (Table 2S ) and
showed a significant association in all subgroups for gender, baseline BMI,
type of surgery, and follow-up duration.
Effect of bariatric surgery on circulating resistin, visfatin, PAI-1, and
chemerin
Seven prospective articles with 330 participants reported resistin as an
outcome measure. Pooled effect size indicated no effect of bariatric surgery
on circulating resistin (–2.080 ng/ml, 95%
CI: –5.352, 1.192, p=0.21) ([Fig. 2c ]). There was no significant
heterogeneity between studies (I2= 98.5%,
p<0.001), and subgroup analysis revealed no association for baseline
BMI, type of surgery, and follow-up period (Table 2S ).
Overall, 8 studies with 171 participants assessed PAI-1 as an outcome
measure. Pooled effect size showed that serum PAI-1 decreased significantly
following bariatric surgery (–14.928 ng/ml
95% CI: –21.794, –8.063, p<0.001) with
significant heterogeneity among included studies (I2= 94.7
%, p<0.001) ([Fig.
2b ]).
Finally, three studies reported chemerin as an outcome measure following
bariatric surgery, that resulted in reduced circulating concentrations
(–50.238 ng/ml 95% CI: –85.708,
–14.768, p<0.001) with significant heterogeneity between
included studies (I2= 0.0%, p<0.001)
([Fig. 2d ]).
Seven studies assessed circulating visfatin following bariatric surgery
(2.05 ng/ml, 95% CI: –5.07, 9.17,
p=0.573). Between-study heterogeneity was significant
(I2= 99.3%, p<0.001) ([Fig. 2a ]).
Sensitivity analysis
Sensitivity analysis revealed that overall estimates of effect size were not
excessively influenced by any of included studies significantly for
adiponectin, leptin, chemerin, PAI-1, and visfatin. Pooled effect size for
resistin showed significant effect following elimination study of
Navaneethan et al. [82 ]
(–3.63 ng/ml, 95% CI: –6.87,
–0.39, I2= 98.3%).
Publication bias and trim and fill analysis
Publication bias analysis was found for studies reporting adiponectin and
leptin. Therefore, following trim and fill analysis were performed for these
two factors. The modified estimate of pooled effect size for adiponectin,
from 64 hypothesized studies changed but remained significantly increased
following bariatric surgery (0.819, 95% CI: 0.45, 1.188,
p<0.001). Trim and fill sensitivity analysis for leptin showed that
overall estimate of effect size from 70 hypothesized negative unpublished
studies did not change (–2.178, 95% CI: –4.33,
–1.923), and remained significant (p<0.001). Publication
bias did not appear to affect these results. There was no evidence of
publication bias for studies examining the effect of bariatric surgery on
PAI-1 (p=0.453, Begg’s test), resistin (p=0.4,
Begg’s test), and visfatin (p=0.54, Begg’s
test).
Meta-Regression analysis
Meta-regression indicated that there was not a linear association between the
change in serum adipokine with baseline BMI of participants [i. e.,
adiponectin (p=0.41), leptin (p=0.49), PAI-1
(p=0.31), and resistin (0.33)]. Moreover, no significant
associations with follow up duration and changes in adiponectin
(p=0.85), leptin (p=0.39), PAI-1 (p=0.82), visfatin
(p=0.61), and resistin (p=0.4) were found. There was a
significant association between the change in visfatin and baseline BMI of
participants (β coefficient=3.6, p=0.026).
Discussion
Our comprehensive meta-analysis has shown that circulating leptin, chemerin, and
PAI-1 decreased after bariatric surgery, whereas adiponectin decreased, and both
visfatin and resistin were unchanged.
Adiponectin is an adipokine, which is not secreted exclusively by the adipose tissue
[113 ], but a range of human tissues [114 ]. Obesity is associated with decreased
adiponectin, that in turn is linked to reduced insulin sensitivity [115 ]. Increased adiponectin status, mediated by
enhanced action, or function of adiponectin receptors (AdipoR) [116 ], or pharmacological elevation of
adiponectin can relieve obesity-related health problems [114 ]. For instance, thiazolidinediones (TZDs)
or other medicinal herbs like Zataria or astragaloside II can increase circulating
adiponectin, and improve insulin sensitivity [117 ]
[118 ]
[119 ]
[120 ]. In addition to pharmacological
interventions, exercise and training can also raise plasma adiponectin [121 ]
[122 ]
[123 ], and would be predicted to ameliorate
obesity-related health problems like DM and CVD, given the cardio-protective effects
of adiponectin [124 ]. The positive effect of
all types of bariatric surgery on circulating adiponectin, irrespective of baseline
BMI and gender, would therefore be expected to represent a beneficial outcome, as
would the decrease in leptin, that has a range of physiological functions including
appetite regulation, and energy homeostasis [125 ]. Serum leptin level is correlated with resting metabolic rate (RMR)
in some but not all studies [126 ], and obesity
is accompanied with leptin resistance [127 ].
Raised leptin has also been found with insulin resistance, DM [128 ], and thickening of the intima-media
thickness with the onset of atherosclerosis [128 ]. Reduced leptin with bariatric surgery, occurs concurrently with
loss of body fat, and has also been seen with exercise and dietary interventions
[128 ]
[129 ].
Increased circulating PAI-1 with obesity is well documented [130 ], and is an established risk factor for
coronary artery disease, atherosclerosis, and stroke [131 ]
[132 ]. Conversely lowering PAI-I reduces the
risk of CVD [133 ], so the decrease with
bariatric surgery would be expected to be beneficial. Resistin is a pro-inflammatory
cytokine that can modulate substrate metabolism through blocking the action of
insulin [134 ], as well as the onset of CVD,
due to inflammation, endothelial and smooth muscle cell dysfunction, thrombosis, and
angiogenesis [134 ]
[135 ]. It was, however, unaffected by
bariatric surgery as was visfatin. This adipokine can modulate inflammation, and is
raised with obesity, DM, metabolic syndrome, and CVD [18 ]
[136 ]
[137 ]. Chemerin also contributed to
adipogenesis, glucose homeostasis, food intake, and body weight; and elevated
chemerin with obesity has been implicated in the onset of DM [138 ]
[139 ]
[140 ]. Bariatric surgery decreased chemerin,
but the lack of eligible studies for chemerin and significant sensitivity analysis
for resistin suggests these findings must be interpreted with caution, and larger
scale studies are needed.
Our meta-analysis has both strengths and limitations, and is the first such study
of
its kind. Although there were sufficient studies investigating the effects of
bariatric surgery on leptin and adiponectin the lack of eligible studies for the
other adipokines limits the interpretation of this data. In addition, the effects
of
confounding factors including, genetic background and other lifestyle modification
remained unclear, together with the potential effects of different types of
bariatric surgery.
Conclusion
In conclusion, our meta-analysis of prospective and retrospective studies show that
bariatric surgery has a beneficial effect on several adipokines including reduced
leptin, chemerin and PAI-1, and increased adiponectin, but has no effect on resistin
and visfatin. However, these results must be interpreted with caution especially for
adipokines with fewer eligible studies for quantitative analysis.
