Resting-state brain connectivity changes in obese women after Roux-en-Y gastric bypass surgery: A longitudinal study

Relationship between functional connectivity and weight-gain risk of antipsychotics in schizophrenia

BACKGROUND

The mechanisms by which antipsychotic medications (APs) contribute to obesity in schizophrenia are not well understood. Because AP effects on functional brain connectivity may contribute to weight effects, the current study investigated how AP-associated weight-gain risk relates to functional connectivity in schizophrenia.

METHODS

Fifty-five individuals with schizophrenia (final N = 54) were divided into groups based on previously reported AP weight-gain risk (no APs/low risk [N = 19]; moderate risk [N = 17]; high risk [N = 18]). Resting-state functional magnetic resonance imaging (fMRI) was completed after an overnight fast ("fasted") and post-meal ("fed"). Correlations between AP weight-gain risk and functional connectivity were assessed at the whole-brain level and in reward- and eating-related brain regions (anterior insula, caudate, nucleus accumbens).

RESULTS

When fasted, greater AP weight-gain risk was associated with increased connectivity between thalamus and sensorimotor cortex (pFDR = 0.021). When fed, greater AP weight-gain risk was associated with increased connectivity between left caudate and left precentral/postcentral gyri (pFDR = 0.048) and between right caudate and multiple regions, including the left precentral/postcentral gyri (pFDR = 0.001), intracalcarine/precuneal/cuneal cortices (pFDR < 0.001), and fusiform gyrus (pFDR = 0.008). When fed, greater AP weight-gain risk was also associated with decreased connectivity between right anterior insula and ventromedial prefrontal cortex (pFDR = 0.002).

CONCLUSIONS

APs with higher weight-gain risk were associated with greater connectivity between reward-related regions and sensorimotor regions when fasted, perhaps relating to motor anticipation for consumption. Higher weight-gain risk APs were also associated with increased connectivity between reward, salience, and visual regions when fed, potentially reflecting greater desire for consumption following satiety.

Obesity surgery and neural correlates of human eating behaviour: A systematic review of functional MRI studies

Changes in eating behaviour including reductions in appetite and food intake, and healthier food cue reactivity, reward, hedonics and potentially also preference, contribute to weight loss and its health benefits after obesity surgery. Functional magnetic resonance imaging (fMRI) has been increasingly used to interrogate the neural correlates of eating behaviour in obesity, including brain reward-cognitive systems, changes after obesity surgery, and links with alterations in the gut-hormone-brain axis. Neural responses to food cues can be measured by changes in blood oxygen level dependent (BOLD) signal in brain regions involved in reward processing, including caudate, putamen, nucleus accumbens, insula, amygdala, orbitofrontal cortex, and top-down inhibitory control, including dorsolateral prefrontal cortex (dlPFC). This systematic review aimed to examine: (i) results of human fMRI studies involving obesity surgery, (ii) important methodological differences in study design across studies, and (iii) correlations and associations of fMRI findings with clinical outcomes, other eating behaviour measures and mechanistic measures. Of 741 articles identified, 23 were eligible for inclusion: 16 (69.6%) longitudinal, two (8.7%) predictive, and five (21.7%) cross-sectional studies. Seventeen studies (77.3%) included patients having Roux-en-Y gastric bypass (RYGB) surgery, six (26.1%) vertical sleeve gastrectomy (VSG), and five (21.7%) laparoscopic adjustable gastric banding (LAGB). The majority of studies (86.0%) were identified as having a very low risk of bias, though only six (27.3%) were controlled interventional studies, with none including randomisation to surgical and control interventions. The remaining studies (14.0%) had a low risk of bias driven by their control groups not having an active treatment. After RYGB surgery, food cue reactivity often decreased or was unchanged in brain reward systems, and there were inconsistent findings as to whether reductions in food cue reactivity was greater for high-energy than low-energy foods. There was minimal evidence from studies of VSG and LAGB surgeries for changes in food cue reactivity in brain reward systems, though effects of VSG surgery on food cue reactivity in the dlPFC were more consistently found. There was consistent evidence for post-operative increases in satiety gut hormones glucagon-like-peptide 1 (GLP-1) and peptide YY (PYY) mediating reduced food cue reactivity after RYGB surgery, including two interventional studies. Methodological heterogeneity across studies, including nutritional state, nature of food cues, post-operative timing, lack of control groups for order effects and weight loss or dietary/psychological advice, and often small sample sizes, limited the conclusions that could be drawn, especially for correlational analyses with clinical outcomes, other eating behaviour measures and potential mediators. This systematic review provides a detailed data resource for those performing or analysing fMRI studies of obesity surgery and makes suggestions to help improve reporting and design of such studies, as well as future directions.

Effects of bariatric surgery and dietary interventions for obesity on brain neurotransmitter systems and metabolism: A systematic review of positron emission tomography (PET) and single-photon emission computed tomography (SPECT) studies

This systematic review collates studies of dietary or bariatric surgery interventions for obesity using positron emission tomography and single-photon emission computed tomography. Of 604 publications identified, 22 met inclusion criteria. Twelve studies assessed bariatric surgery (seven gastric bypass, five gastric bypass/sleeve gastrectomy), and ten dietary interventions (six low-calorie diet, three very low-calorie diet, one prolonged fasting). Thirteen studies examined neurotransmitter systems (six used tracers for dopamine DRD2/3 receptors: two each for 11 C-raclopride, 18 F-fallypride, 123 I-IBZM; one for dopamine transporter, 123 I-FP-CIT; one used tracer for serotonin 5-HT2A receptor, 18 F-altanserin; two used tracers for serotonin transporter, 11 C-DASB or 123 I-FP-CIT; two used tracer for μ-opioid receptor, 11 C-carfentanil; one used tracer for noradrenaline transporter, 11 C-MRB); seven studies assessed glucose uptake using 18 F-fluorodeoxyglucose; four studies assessed regional cerebral blood flow using 15 O-H2 O (one study also used arterial spin labeling); and two studies measured fatty acid uptake using 18 F-FTHA and one using 11 C-palmitate. The review summarizes findings and correlations with clinical outcomes, eating behavior, and mechanistic mediators. The small number of studies using each tracer and intervention, lack of dietary intervention control groups in any surgical studies, heterogeneity in time since intervention and degree of weight loss, and small sample sizes hindered the drawing of robust conclusions across studies.

Higher body weight-dependent neural activation during reward processing

Obesity is associated with alterations in brain structure and function, particularly in areas related to reward processing. Although brain structural investigations have demonstrated a continuous association between higher body weight and reduced gray matter in well-powered samples, functional neuroimaging studies have typically only contrasted individuals from the normal weight and obese body mass index (BMI) ranges with modest sample sizes. It remains unclear, whether the commonly found hyperresponsiveness of the reward circuit can (a) be replicated in well-powered studies and (b) be found as a function of higher body weight even below the threshold of clinical obesity. 383 adults across the weight spectrum underwent functional magnetic resonance imaging during a common card-guessing paradigm simulating monetary reward. Multiple regression was used to investigate the association of BMI and neural activation in the reward circuit. In addition, a one-way ANOVA model comparing three weight groups (normal weight, overweight, obese) was calculated. Higher BMI was associated with higher reward response in the bilateral insula. This association could no longer be found when participants with obesity were excluded from the analysis. The ANOVA revealed higher activation in obese vs. lean, but no difference between lean and overweight participants. The overactivation of reward-related brain areas in obesity is a consistent finding that can be replicated in large samples. In contrast to brain structural aberrations associated with higher body weight, the neurofunctional underpinnings of reward processing in the insula appear to be more pronounced in the higher body weight range.

Resting-state network functional connectivity before and after bariatric surgery

BACKGROUND

Bariatric surgery is an increasingly popular treatment for patients with severe obesity and related health issues (e.g., diabetes, cardiovascular disease). Studies have identified alterations in functional connectivity both in obesity and following surgical treatment for severe obesity.

OBJECTIVE

This study aimed to assess brain function via resting-state within-network connectivity in bariatric surgery patients with severe obesity.

SETTING

University hospital.

METHODS

Thirty-four bariatric surgery patients completed functional neuroimaging at baseline and postoperatively (goal, 12 weeks; actual, 16 weeks, on average). They also self-reported health information. Baseline resting-state functional connectivity (RSFC) was predicted by baseline age, body mass index (BMI), continuous positive airway pressure use, and reported history of rheumatoid arthritis and type 2 diabetes. Change in RSFC was assessed using the same predictors. This model was run with and without controlling for baseline RSFC.

RESULTS

Higher baseline BMI predicted lower baseline RSFC in 3 networks. Lower baseline RSFC also was related to rheumatoid arthritis and type 2 diabetes. Difference between baseline and follow-up RSFC was strongly negatively associated with baseline RSFC. Controlling for baseline RSFC, type 2 diabetes negatively predicted RSFC difference.

CONCLUSIONS

RSFC may reflect brain dysfunction in patients with obesity and related diseases. That less connectivity at baseline predicted greater positive change suggests that RSFC may be a biomarker of neurocognitive improvement following bariatric surgery. Diseases more prevalent in patients with obesity (e.g., rheumatoid arthritis and type 2 diabetes) along with elevated BMI negatively affect RSFC likely through inflammatory pathways.

Brain functional and structural magnetic resonance imaging of obesity and weight loss interventions

Obesity has tripled over the past 40 years to become a major public health issue, as it is linked with increased mortality and elevated risk for various physical and neuropsychiatric illnesses. Accumulating evidence from neuroimaging studies suggests that obesity negatively affects brain function and structure, especially within fronto-mesolimbic circuitry. Obese individuals show abnormal neural responses to food cues, taste and smell, resting-state activity and functional connectivity, and cognitive tasks including decision-making, inhibitory-control, learning/memory, and attention. In addition, obesity is associated with altered cortical morphometry, a lowered gray/white matter volume, and impaired white matter integrity. Various interventions and treatments including bariatric surgery, the most effective treatment for obesity in clinical practice, as well as dietary, exercise, pharmacological, and neuromodulation interventions such as transcranial direct current stimulation, transcranial magnetic stimulation and neurofeedback have been employed and achieved promising outcomes. These interventions and treatments appear to normalize hyper- and hypoactivations of brain regions involved with reward processing, food-intake control, and cognitive function, and also promote recovery of brain structural abnormalities. This paper provides a comprehensive literature review of the recent neuroimaging advances on the underlying neural mechanisms of both obesity and interventions, in the hope of guiding development of novel and effective treatments.

Exercise modifies hypothalamic connectivity and brain functional networks in women after bariatric surgery: a randomized clinical trial

BACKGROUND

Obesity is a disease that may involve disrupted connectivity of brain networks. Bariatric surgery is an effective treatment for obesity, and the positive effects on obesity-related conditions may be enhanced by exercise. Herein, we aimed to investigate the possible synergistic effects of Roux-en-Y Gastric Bypass (RYGB) and exercise training on brain functional networks.

METHODS

Thirty women eligible for bariatric surgery were randomly assigned to a Roux-en-Y gastric bypass (RYGB: n = 15, age = 41.0 ± 7.3 years) or RYGB plus Exercise Training (RYGB + ET: n = 15, age = 41.9 ± 7.2 years). Clinical, laboratory, and brain functional connectivity parameters were assessed at baseline, and 3 (POST3) and 9 months (POST9) after surgery. The 6-month, three-times-a-week, exercise intervention (resistance plus aerobic exercise) was initiated 3 months post-surgery (for RYGB + ET).

RESULTS

Exercise superimposed on bariatric surgery (RYGB + ET) increased connectivity between hypothalamus and sensorial regions (seed-to-voxel analyses of hypothalamic connectivity), and decreased default mode network (DMN) and posterior salience (pSAL) network connectivity (ROI-to-ROI analyses of brain networks connectivity) when compared to RYGB alone (all p-FDR < 0.05). Increases in basal ganglia (BG) network connectivity were only observed in the exercised training group (within-group analyses).

CONCLUSION

Exercise training is an important component in the management of post-bariatric patients and may improve the hypothalamic connectivity and brain functional networks that are involved in controlling food intake.

TRIAL REGISTRATION

Clinicaltrial.gov: NCT02441361.

Effects of gastric bypass surgery on brain connectivity responses to hypoglycemia

INTRODUCTION

Roux-en-Y gastric bypass (RYGB) leads to beneficial effects on glucose homeostasis, and attenuated hormonal counterregulatory responses to hypoglycemia are likely to contribute. RYGB also induces alterations in neural activity of cortical and subcortical brain regions. We aimed to characterize RYGB-induced changes in resting-state connectivity of specific brain regions of interest for energy homeostasis and behavioral control during hypoglycemia.

METHOD

Ten patients with BMI > 35 kg/m2 were investigated with brain PET/MR imaging during a hyperinsulinemic normo- and hypoglycemic clamp, before and 4 months after RYGB. Hormonal levels were assessed throughout the clamp. Resting-state (RS) fMRI scans were acquired in the glucose-lowering phase of the clamp, and they were analyzed with a seed-to-voxel approach.

RESULTS

RS connectivity during initiation of hypoglycemia was significantly altered after RYGB between nucleus accumbens, thalamus, caudate, hypothalamus and their crosstalk with cortical and subcortical regions. Connectivity between the nucleus accumbens and the frontal pole was increased after RYGB, and this was associated with a reduction of ACTH (r = -0.639, p = 0.047) and cortisol (r = -0.635, p = 0.048) responses. Instead, connectivity between the caudate and the frontal pole after RYGB was reduced and this was associated with less attenuation of glucagon response during the hypoglycemic clamp (r = -0.728, p = 0.017), smaller reduction in fasting glucose (r = -0.798, p = 0.007) and less excess weight loss (r = 0.753, p = 0.012). No other significant associations were found between post-RYGB changes in ROI-to-voxel regional connectivity hormonal responses and metabolic or anthropometric outcomes.

CONCLUSION

RYGB alters brain connectivity during hypoglycemia of several neural pathways involved in reward, inhibitory control, and energy homeostasis. These changes are associated with altered hormonal responses to hypoglycemia and may be involved in the glucometabolic outcome of RYGB.

Regulation of body weight: Lessons learned from bariatric surgery

BACKGROUND

Bariatric or weight loss surgery is currently the most effective treatment for obesity and metabolic disease. Unlike dieting and pharmacology, its beneficial effects are sustained over decades in most patients, and mortality is among the lowest for major surgery. Because there are not nearly enough surgeons to implement bariatric surgery on a global scale, intensive research efforts have begun to identify its mechanisms of action on a molecular level in order to replace surgery with targeted behavioral or pharmacological treatments. To date, however, there is no consensus as to the critical mechanisms involved.

SCOPE OF REVIEW

The purpose of this non-systematic review is to evaluate the existing evidence for specific molecular and inter-organ signaling pathways that play major roles in bariatric surgery-induced weight loss and metabolic benefits, with a focus on Roux-en-Y gastric bypass (RYGB) and vertical sleeve gastrectomy (VSG), in both humans and rodents.

MAJOR CONCLUSIONS

Gut-brain communication and its brain targets of food intake control and energy balance regulation are complex and redundant. Although the relatively young science of bariatric surgery has generated a number of hypotheses, no clear and unique mechanism has yet emerged. It seems increasingly likely that the broad physiological and behavioral effects produced by bariatric surgery do not involve a single mechanism, but rather multiple signaling pathways. Besides a need to improve and better validate surgeries in animals, advanced techniques, including inducible, tissue-specific knockout models, and the use of humanized physiological traits will be necessary. State-of-the-art genetically-guided neural identification techniques should be used to more selectively manipulate function-specific pathways.

A systematic review of resting-state functional connectivity in obesity: Refining current neurobiological frameworks and methodological considerations moving forward

Obesity is the second most common cause of preventable morbidity worldwide. Resting-state functional magnetic resonance imaging (fMRI) has been used extensively to characterise altered communication between brain regions in individuals with obesity, though findings from this research have not yet been systematically evaluated within the context of prominent neurobiological frameworks. This systematic review aggregated resting-state fMRI findings in individuals with obesity and evaluated the contribution of these findings to current neurobiological models. Findings were considered in relation to a triadic model of problematic eating, outlining disrupted communication between reward, inhibitory, and homeostatic systems. We identified a pattern of consistently increased orbitofrontal and decreased insula cortex resting-state functional connectivity in individuals with obesity in comparison to healthy weight controls. BOLD signal amplitude was also increased in people with obesity across studies, predominantly confined to subcortical regions, including the hippocampus, amygdala, and putamen. We posit that altered orbitofrontal cortex connectivity may be indicative of a shift in the valuation of food-based rewards and that dysfunctional insula connectivity likely contributes to altered homeostatic signal processing. Homeostatic violation signals in obesity may be maintained despite satiety, thereby 'hijacking' the executive system and promoting further food intake. Moving forward, we provide a roadmap for more reliable resting-state and task-based functional connectivity experiments, which must be reconciled within a common framework if we are to uncover the interplay between psychological and biological factors within current theoretical frameworks.

Computational approaches to predicting treatment response to obesity using neuroimaging

Obesity is a worldwide disease associated with multiple severe adverse consequences and comorbid conditions. While an increased body weight is the defining feature in obesity, etiologies, clinical phenotypes and treatment responses vary between patients. These variations can be observed within individual treatment options which comprise lifestyle interventions, pharmacological treatment, and bariatric surgery. Bariatric surgery can be regarded as the most effective treatment method. However, long-term weight regain is comparably frequent even for this treatment and its application is not without risk. A prognostic tool that would help predict the effectivity of the individual treatment methods in the long term would be essential in a personalized medicine approach. In line with this objective, an increasing number of studies have combined neuroimaging and computational modeling to predict treatment outcome in obesity. In our review, we begin by outlining the central nervous mechanisms measured with neuroimaging in these studies. The mechanisms are primarily related to reward-processing and include "incentive salience" and psychobehavioral control. We then present the diverse neuroimaging methods and computational prediction techniques applied. The studies included in this review provide consistent support for the importance of incentive salience and psychobehavioral control for treatment outcome in obesity. Nevertheless, further studies comprising larger sample sizes and rigorous validation processes are necessary to answer the question of whether or not the approach is sufficiently accurate for clinical real-world application.

Long-term changes in insula-mesolimbic structural and functional connectivity in obese patients after laparoscopic sleeve gastrectomy

OBJECTIVE

Brain imaging studies have shown insula-related functional and structural abnormalities in patients with obesity. Laparoscopic sleeve gastrectomy is currently an effective procedure for treating obesity, which promotes acute recovery of brain functional and structural abnormalities in obese patients. The aim of this study was to investigate the long-term impact of laparoscopic sleeve gastrectomy on insula-related structural and functional connectivity.

METHODS

Diffusion tensor imaging and resting-state functional magnetic resonance imaging were employed to investigate laparoscopic sleeve gastrectomy-induced changes in insula-related structural connectivity and corresponding resting-state functional connectivity in 25 obese patients prior to (PreLSG) and 12 months post-surgery (PostLSG₁₂).

RESULTS

Results showed significant increases in fractional anisotropy and axial diffusivity between the right insula and anterior cingulate cortex, and higher fractional anisotropy of left insula-putamen, left insula-caudate and anterior cingulate cortex-right posterior cingulate cortex/precuneus at PostLSG12 compared with PreLSG. There were significant negative correlations between axial diffusivity of right insula-anterior cingulate cortex and body mass index, and fractional anisotropy of right insula-anterior cingulate cortex with scores on external eating at PostLSG12. Anxiety and depressive status ratings were negatively correlated with fractional anisotropy of left insula-putamen at PostLSG12. In addition, there was a significant decrease in resting-state functional connectivity between left insula and left caudate.

CONCLUSIONS

These findings demonstrate long-term changes in insula-related structural and functional connectivity abnormalities promoted by laparoscopic sleeve gastrectomy, which highlight its strong association with long-term weight loss and improvement in eating behaviors.

Roux-En-Y Gastric Bypass (RYGB) Surgery during High Liquid Sucrose Diet Leads to Gut Microbiota-Related Systematic Alterations

Roux-en-Y gastric bypass (RYGB) surgery has been proven successful in weight loss and improvement of co-morbidities associated with obesity. Chronic complications such as malabsorption of micronutrients in up to 50% of patients underline the need for additional therapeutic approaches. We investigated systemic RYGB surgery effects in a liquid sucrose diet-induced rat obesity model. After consuming a diet supplemented with high liquid sucrose for eight weeks, rats underwent RYGB or control sham surgery. RYGB, sham pair-fed, and sham ad libitum-fed groups further continued on the diet after recovery. Notable alterations were revealed in microbiota composition, inflammatory markers, feces, liver, and plasma metabolites, as well as in brain neuronal activity post-surgery. Higher fecal 4-aminobutyrate (GABA) correlated with higher Bacteroidota and Enterococcus abundances in RYGB animals, pointing towards the altered enteric nervous system (ENS) and gut signaling. Favorable C-reactive protein (CRP), serine, glycine, and 3-hydroxybutyrate plasma profiles in RYGB rats were suggestive of reverted obesity risk. The impact of liquid sucrose diet and caloric restriction mainly manifested in fatty acid changes in the liver. Our multi-modal approach reveals complex systemic changes after RYGB surgery and points towards potential therapeutic targets in the gut-brain system to mimic the surgery mode of action.

Behavioral Interventions to Attenuate Driven Overeating and Weight Regain After Bariatric Surgery

Weight regain after bariatric surgery is associated with problematic eating behaviors that have either recurred after a period of improvement or are new-onset behaviors. Problematic eating behaviors after bariatric surgery have been conceptualized in different ways in the literature, such as having a food addiction and experiencing a loss of control of eating. The intersection of these constructs appears to be driven overeating defined as patients' experiences of reduced control of their eating which results in overeating behavior. The purpose of this review is to define patient experiences of driven overeating through the behavioral expression of emotion-based eating, reward-based eating, and executive functioning deficits-namely impulsivity-which is associated with weight regain after having bariatric surgery. Delineating concepts in this way and determining treatment strategies accordingly may reduce distress related to the inevitable return of increased hunger, cravings, portion sizes, and tolerance for highly palatable foods after surgery. Along with standard behavioral weight maintenance strategies, topics including acceptance, motivation, emotion-based eating, reward-based/impulsive eating, physical activity, and self-compassion are discussed. These concepts have been adapted for patients experiencing weight regain after having bariatric surgery and may be particularly helpful in attenuating driven overeating and weight regain.

Bariatric surgery and alcohol and substance abuse disorder: A systematic review

INTRODUCTION

Bariatric surgery is a relatively safe surgical procedure with a high success rate. However, recent reports indicate a higher prevalence of alcohol or substance abuse disorder in this patient group. The purpose of this study was to review the related evidence to serve as a reference for multidisciplinary teams who treat these patients.

METHODS

We searched the PubMed and CENTRAL databases. The odds ratios were extracted from the different articles, comparing the prevalence of the abuse of alcohol or other substances in the postoperative period versus preoperative levels. We also compared the prevalence of alcohol use disorder after different types of bariatric surgery.

RESULTS

A total of 49 121 bariatric patients (80.8% female) were evaluated for alcohol use disorder. In general, bariatric surgery was found to be associated with an increase in the prevalence of alcohol abuse (4.58 ± 5.3 vs. 1.58 ± 10.7% in the preoperative period). We also found that the population of patients who underwent RYGB procedures had a higher prevalence of alcohol use disorder than patients who underwent another type of surgery (OR: 1.83; 95% CI: 1.51-2.21). The prevalence of substance abuse disorder (other than alcohol) after this procedure is less studied, although there appears to be an increased risk of abuse of certain substances.

CONCLUSIONS

Bariatric surgery is the best treatment for obesity and its complications. The evidence reviewed suggests that it correlates with a modest but consistent increase in the prevalence of abuse of alcohol and other substances. Medical teams who treat bariatric patients must be informed about this eventuality for its timely prevention, diagnosis and treatment.

A systematic review and meta-analyses of food preference modifications after bariatric surgery

This systematic review and meta-analyses aimed to synthesize evidence of the link between bariatric surgery and changes in food preferences, considering the method of assessment. MEDLINE, Cochrane Library, Web of Science, Cinahl, PsychINFO, ProQuest, and Open grey were searched incorporating two blocks of terms ("Intervention" and "Food Preferences"). Interventional or observational studies involving patients (BMI ≥ 35 kg m^-2 ) with sleeve gastrectomy (SG) or Roux-en-Y Gastric Bypass (RYGB) and a control group were included. Meta-analyses were performed comparing the standardized daily mean percentage energy from proteins, carbohydrates, and lipids between preoperative and postoperative patients. Fifty-seven studies concerning 2,271 patients with RYGB and 903 patients with SG met the inclusion criteria, of which 24 were eligible for meta-analysis. Despite a total reduction in macronutrient intakes, the meta-analyses revealed a postoperative increase in percentage energy from proteins at 12 months (0.24, 95% CI: 0.03, 0.46, {I² } = 73%) and a decrease in percentage energy from fat at 1 month (-0.47, 95% CI: 0.86, 0.09, {I² } = 72%), up to 24 months (-0.20, 95% CI: -0.31, 0.08, {I² } = 0%). In conclusion, the present systematic review and meta-analyses showed changes of food preferences in terms of macronutrient, food selection and, overall food appreciation up to 5 years following bariatric surgery.

Effects of bariatric surgery on functional connectivity of the reward and default mode network: A pre-registered analysis

Obesity imposes serious health risks and involves alterations in resting‐state functional connectivity of brain networks involved in eating behavior. Bariatric surgery is an effective treatment, but its effects on functional connectivity are still under debate. In this pre‐registered study, we aimed to determine the effects of bariatric surgery on major resting‐state brain networks (reward and default mode network) in a longitudinal controlled design. Thirty‐three bariatric surgery patients and 15 obese waiting‐list control patients underwent magnetic resonance imaging at baseline, after 6 and 12 months. We conducted a pre‐registered whole‐brain time‐by‐group interaction analysis, and a time‐by‐group interaction analysis on within‐network connectivity. In exploratory analyses, we investigated the effects of weight loss and head motion. Bariatric surgery compared to waiting did not significantly affect functional connectivity of the reward network and the default mode network (FWE‐corrected p > .05), neither whole‐brain nor within‐network. In exploratory analyses, surgery‐related BMI decrease (FWE‐corrected p = .041) and higher average head motion (FWE‐corrected p = .021) resulted in significantly stronger connectivity of the reward network with medial posterior frontal regions. This pre‐registered well‐controlled study did not support a strong effect of bariatric surgery, compared to waiting, on major resting‐state brain networks after 6 months. Exploratory analyses indicated that head motion might have confounded the effects. Data pooling and more rigorous control of within‐scanner head motion during data acquisition are needed to substantiate effects of bariatric surgery on brain organization.

Dysregulated resting state functional connectivity and obesity: A systematic review

Obesity has been variously linked to differences in brain functional connectivity in regions associated with reward, emotional regulation and cognition, potentially revealing neural mechanisms contributing to its development and maintenance. This systematic review summarizes and critically appraises the existing literature on differences in resting state functional connectivity (Rs-FC) between overweight and individuals with obesity in relation healthy-BMI controls. Twenty-nine studies were identified and the results consistently support the hypothesis that obesity is associated with differences in Rs-FC. Specifically, obesity/overweight was consistently associated with (i) DMN hypoconnectivity and salience network hyperconnectivity; (ii) increased Rs-FC between the hypothalamus and reward, limbic and salience networks, and decreased Rs-FC between the hypothalamus and cognitive regions; (iii) increased power within regions associated with inhibition/emotional reasoning; (iv) decreased nodal efficiency, degree centrality, and global efficiency. Collectively, the results suggest obesity is associated with disrupted connectivity of brain networks responsible for cognition, reward, self-referential processing and emotional regulation.

Reversal of Functional Brain Activity Related to Gut Microbiome and Hormones After VSG Surgery in Patients With Obesity

CONTEXT

Vertical sleeve gastrectomy (VSG) is becoming a prioritized surgical intervention for obese individuals; however, the brain circuits that mediate its effective control of food intake and predict surgical outcome remain largely unclear.

OBJECTIVE

We investigated VSG-correlated alterations of the gut-brain axis.

METHODS

In this observational cohort study, 80 patients with obesity were screened. A total of 36 patients together with 26 normal-weight subjects were enrolled and evaluated using the 21-item Three-Factor Eating Questionnaire (TFEQ), MRI scanning, plasma intestinal hormone analysis, and fecal sample sequencing. Thirty-two patients underwent VSG treatment and 19 subjects completed an average of 4-month follow-up evaluation. Data-driven regional homogeneity (ReHo) coupled with seed-based connectivity analysis were used to quantify VSG-related brain activity. Longitudinal alterations of body weight, eating behavior, brain activity, gastrointestinal hormones, and gut microbiota were detected and subjected to repeated measures correlation analysis.

RESULTS

VSG induced significant functional changes in the right putamen (PUT.R) and left supplementary motor area, both of which correlated with weight loss and TFEQ scores. Moreover, postprandial levels of active glucagon-like peptide-1 (aGLP-1) and Ghrelin were associated with ReHo of PUT.R; meanwhile, relative abundance of Clostridia increased by VSG was associated with improvements in aGLP-1 secretion, PUT.R activity, and weight loss. Importantly, VSG normalized excessive functional connectivities with PUT.R, among which baseline connectivity between PUT.R and right orbitofrontal cortex was related to postoperative weight loss.

CONCLUSION

VSG causes correlated alterations of gut-brain axis, including Clostridia, postprandial aGLP-1, PUT.R activity, and eating habits. Preoperative connectivity of PUT.R may represent a potential predictive marker of surgical outcome in patients with obesity.

Bariatric surgery and alcohol and substance abuse disorder: A systematic review

INTRODUCTION

Bariatric surgery is a relatively safe surgical procedure with a high success rate. However, recent reports indicate a higher prevalence of alcohol or substance abuse disorder in this patient group. The purpose of this study was to review the related evidence to serve as a reference for multidisciplinary teams who treat these patients.

METHODS

We searched the PubMed and CENTRAL databases. The odds ratios were extracted from the different articles, comparing the prevalence of the abuse of alcohol or other substances in the postoperative period versus preoperative levels. We also compared the prevalence of alcohol use disorder after different types of bariatric surgery.

RESULTS

A total of 49 121 bariatric patients (80.8% female) were evaluated for alcohol use disorder. In general, bariatric surgery was found to be associated with an increase in the prevalence of alcohol abuse (4.58±5.3 vs. 1.58±10.7% in the preoperative period). We also found that the population of patients who underwent RYGB procedures had a higher prevalence of alcohol use disorder than patients who underwent another type of surgery (OR: 1.83; 95% CI: 1.51-2.21). The prevalence of substance abuse disorder (other than alcohol) after this procedure is less studied, although there appears to be an increased risk of abuse of certain substances.

CONCLUSIONS

Bariatric surgery is the best treatment for obesity and its complications. The evidence reviewed suggests that it correlates with a modest but consistent increase in the prevalence of abuse of alcohol and other substances. Medical teams who treat bariatric patients must be informed about this eventuality for its timely prevention, diagnosis and treatment.

The impact of impulsivity on weight loss after bariatric surgery: a systematic review

BACKGROUND

Impulsivity has been shown to be associated with obesity through links to pathological eating behavior such as binge eating. The recent literature suggests that impulsivity is linked to poorer outcomes post-bariatric surgery. Impulsivity can be measured in various ways and comprises of three broad domains: impulsive choice, impulsive action, and impulsive personality traits. The aim of this systematic review is to synthesize the current evidence on the impact of impulsivity on post-bariatric surgery weight loss.

METHODS

A literature review was performed in February 2020. Original studies investigating the relationship between impulsivity and weight loss post-bariatric surgery were evaluated.

RESULTS

Ten studies with a total of 1246 patients were analyzed. There were four case-control, four prospective observational and two retrospective observational studies. The postoperative follow-up ranged from 0.5 to 12 years. Eight studies measuring trait impulsivity did not show any association with weight loss post-bariatric surgery, although two studies reported an indirect effect of impulsivity on weight loss mediated via pathological eating behavior. Assessment of impulsive action by two studies showed that post-bariatric surgery weight loss is affected by impulsive action.

CONCLUSION

Impulsivity may adversely affect postoperative outcomes after bariatric surgery. However, this may be specific to state impulsivity or impulsive action rather than trait impulsivity. Patients with a higher state impulsivity may benefit from closer follow-up post-bariatric surgery, as well as cognitive behavioral therapies targeting cognitive control over food.

LEVEL OF EVIDENCE

Level I, systematic review.

Resting-state connectivity within the brain's reward system predicts weight loss and correlates with leptin

Weight gain is often associated with the pleasure of eating food rich in calories. This idea is based on the findings that people with obesity showed increased neural activity in the reward and motivation systems of the brain in response to food cues. Such correlations, however, overlook the possibility that obesity may be associated with a metabolic state that impacts the functioning of reward and motivation systems, which in turn could be linked to reactivity to food and eating behaviour and weight gain. In a study involving 44 female participants [14 patients with obesity, aged 20–63 years (mean: 42, SEM: 3.2 years), and 30 matched lean controls, aged 22–60 years (mean: 37, SEM: 1.8 years)], we investigated how ventromedial prefrontal cortex seed-to-voxel resting-state connectivity distinguished between lean and obese participants at baseline. We used the results of this first step of our analyses to examine whether changes in ventromedial prefrontal cortex resting-state connectivity over 8 months could formally predict weight gain or loss. It is important to note that participants with obesity underwent bariatric surgery at the beginning of our investigation period. We found that ventromedial prefrontal cortex–ventral striatum resting-state connectivity and ventromedial–dorsolateral prefrontal cortex resting-state connectivity were sensitive to obesity at baseline. However, only the ventromedial prefrontal cortex–ventral striatum resting-state connectivity predicted weight changes over time using cross-validation, out-of-sample prediction analysis. Such an out-of-sample prediction analysis uses the data of all participants of a training set to predict the actually observed data in one independent participant in the hold-out validation sample and is then repeated for all participants. In seeking to explain the reason why ventromedial pre-frontal cortex–ventral striatum resting-state connectivity as the central hub of the brain’s reward and motivational system may predict weight change over time, we linked weight loss surgery-induced changes in ventromedial prefrontal cortex–ventral striatum resting-state connectivity to surgery-induced changes in homeostatic hormone regulation. More specifically, we focussed on changes in fasting state systemic leptin, a homeostatic hormone signalling satiety, and inhibiting reward-related dopamine signalling. We found that the surgery-induced increase in ventromedial prefrontal cortex–ventral striatum resting-state connectivity was correlated with a decrease in fasting-state systemic leptin. These findings establish the first link between individual differences in brain connectivity in reward circuits in a more tonic state at rest, weight change over time and homeostatic hormone regulation.

The Phantom Satiation Hypothesis of Bariatric Surgery

The excitation of vagal mechanoreceptors located in the stomach wall directly contributes to satiation. Thus, a loss of gastric innervation would normally be expected to result in abrogated satiation, hyperphagia, and unwanted weight gain. While Roux-en-Y-gastric bypass (RYGB) inevitably results in gastric denervation, paradoxically, bypassed subjects continue to experience satiation. Inspired by the literature in neurology on phantom limbs, I propose a new hypothesis in which damage to the stomach innervation during RYGB, including its vagal supply, leads to large-scale maladaptive changes in viscerosensory nerves and connected brain circuits. As a result, satiation may continue to arise, sometimes at exaggerated levels, even in subjects with a denervated or truncated stomach. The same maladaptive changes may also contribute to dysautonomia, unexplained pain, and new emotional responses to eating. I further revisit the metabolic benefits of bariatric surgery, with an emphasis on RYGB, in the light of this phantom satiation hypothesis.

Emotion perception and theory of mind in obesity: a systematic review on the impact of social cognitive deficits on dysfunctional eating behaviors

The aim of this paper was to summarize our current understanding of emotion perception and Theory of Mind (ToM) in obesity and how they relate to dysfunctional eating behaviors (DEB), frequently found in candidates for bariatric surgery. The literature was searched using the electronic databases PsychInfo, Medline, and Web of Science databases, and by additional hand searches through reference lists and specialist eating disorders journals. Relevant studies were included if they were written in English, included participants suffering from obesity and evaluation with tasks assessing social cognition, such as emotion recognition and perception, as well as ToM. Twelve studies analyzed for this systematic review suggest that deficits in such social cognitive domains may lie behind many emotional and social difficulties present in people with obesity, be they bariatric or not, which usually favor DEB. Our review suggests that people with obesity of all ages score significantly less than controls on instruments assessing emotion recognition and ToM, justifying a possible relationship between social cognitive impairments and dysfunctional eating behaviors, such as binges, emotional eating, and addition to food, frequently seen in people with obesity. These findings have important implications for our understanding of the social cognitive foundations of eating behavior in individuals with obesity. They can help not only the presurgical behavioral assessment, but also guide postoperative follow-up of this population.

Decreased emotional eating behavior is associated with greater excess weight loss five years after gastric banding

While significant weight loss has been observed in the first two years following adjustable gastric banding (AGB), research on the long-term effectiveness of gastric restriction (e.g., 5 years) both on weight loss and eating behavior changes is scarce. The present study examined obese patients' changes in eating behavior preoperatively and 5 years after AGB and examined their associations with excess weight loss (EWL). Specifically, we focused on the association between the modification of three eating behavior profiles (i.e., restrained eating, emotional eating and external eating) and %EWL at 5 years. Among the 197 participants who underwent AGB, 136 completed the clinical assessments (weight, depression with the BDI, eating behavior with the DEBQ) before surgery, and after 5 years. Resultsshowed that the mean percentage of EWL was 47% after 5 years. Moreover, patients reported lower emotional eating and external eating after 5 years in comparison to the baseline, whereas there were no differences concerning restrained eating. Importantly, patients who presented higher %EWL at 5 years also reported a greater decrease in emotional eating between the two sessions than those with low %EWL. Our study underlines that eating behaviors are major variables involved in weight loss after gastric restriction. Results showed that emotional and external eating decreased significantly at 5 years whereas restrained eating behaviors did not vary between the pre- and postoperative stages. Moreover, the data suggest that a decrease in emotional eating accounts for the extent of EWL.

Recent Advances in the Neurobiology of Altered Motivation Following Bariatric Surgery

PURPOSE OF REVIEW

There is compelling evidence in the clinical population that long-term weight loss secondary to bariatric surgery is mitigated by the reemergence of maladaptive feeding behaviors and in some cases new onset substance abuse.

RECENT FINDINGS

A review of the current literature suggests that physical restructuring of the GI tract during WLS alters secretion of feeding peptides and nutrient-sensing mechanisms that directly target the brain's endogenous reward system, the mesolimbic dopamine system. Post-surgical changes in GI physiology augment activation of the mesolimbic system. In some patients, this process may contribute to a reduced appetite for palatable food whereas in others it may support maladaptive motivated behavior for food and chemical drugs. It is concluded that future studies are required to detail the timing and duration of surgical-induced changes in GI-mesolimbic communication to more fully understand this phenomenon.

Resting-State Brain Connectivity Predicts Weight Loss and Cognitive Control of Eating Behavior After Vertical Sleeve Gastrectomy

OBJECTIVE

The effects of sleeve gastrectomy (SG) on functional connectivity (FC) and associations with weight loss and eating-related cognitive control were investigated.

METHODS

In a longitudinal study, 14 SG patients (13 female; 42.1 presurgery BMI) completed study visits 1 month pre surgery and 12 months post surgery. Patients completed the Dutch Eating Behavior Questionnaire and resting-state functional magnetic resonance imaging scanning to measure FC. Data were analyzed using a seed-to-voxel approach in the CONN Toolbox to investigate pre-/postsurgery changes (n = 12) and to conduct predictive analysis (n = 14).

RESULTS

Seed-to-voxel analysis revealed changes in magnitude (decreases) and directionality (positively correlated to anticorrelated) of FC pre to post surgery within and between default mode network, salience network, and frontoparietal network nodes [Family-Wise Error (FWE) corrected at P < 0.05]. Baseline FC of the nucleus accumbens (with insula) and hypothalamus (with precentral gyrus) predicted 12-month post-SG % total weight loss (FWE-P < 0.05). Baseline FC of the hippocampus, frontoparietal network, and default mode network nodes predicted improvement in cognitive control of eating behavior 12 months after SG (FWE-P < 0.05).

CONCLUSIONS

Our findings demonstrate changes in FC magnitude and directionality post versus pre surgery within and between resting-state networks and frontal, paralimbic, and visual areas in SG patients. Baseline FC predicted weight loss and changes in cognitive control of food intake behavior at 12 months. These could serve as predictive biomarkers for bariatric surgery.

Neuroimaging correlates of cognitive changes after bariatric surgery

BACKGROUND

Obesity has been associated with cognitive deficits and increased risk for developing dementia. Bariatric surgery may result in improved cognitive function; however, the underlying structural and functional brain correlates are unclear.

OBJECTIVES

This longitudinal study explores the hypothesis that specific brain regions and networks underlie cognitive changes after bariatric surgery.

SETTING

University Hospital, United States.

METHODS

Seventeen patients were recruited for this prospective cohort study, including 9 patients undergoing bariatric surgery, and 8 age-, sex-, and education level-matched healthy, nonobese control patients. Bariatric patients underwent longitudinal neuropsychologic tests and magnetic resonance imaging (MRI) scans both before and 6 months after surgery. One patient was lost to follow-up. The same neuropsychologic tests and MRI scans were performed for control patients. Differences in MRI and neuropsychologic testing between bariatric patients and control patients, and longitudinal changes within bariatric patients were assessed.

RESULTS

At baseline, bariatric patients demonstrated deficits in cognitive function relative to control patients, including pattern comparison (P = .009) and picture sequence memory (P = .004), which improved after significant weight loss. Baseline cognitive deficits in bariatric patients were accompanied by significantly lower left executive control network connectivity on resting-state functional MRI relative to control patients (P = .028), but differences resolved or diminished after bariatric surgery. Longitudinal improvements in pattern comparison performance correlated significantly with increases in left executive control network connectivity (r = .819; P = .013). No significant group or longitudinal differences were found in brain perfusion or brain white matter lesions.

CONCLUSIONS

Individuals with obesity undergoing bariatric surgery exhibit deficits in cognitive function and specific alterations of brain networks; however, cognitive performance can improve, and executive control network connectivity can increase after weight loss from bariatric surgery.

Impact of bariatric surgery on neural food processing and cognition: an fMRI study

INTRODUCTION

The Roux-en-Y gastric bypass (RYGB) is one of the most widely used techniques for bariatric surgery. After RYGB, weight loss up to 50%-70% of excess body weight, improvement of insulin-resistance, changes in food preferences and improvements in cognitive performance have been reported. This protocol describes a longitudinal study of the neural correlates associated with food-processing and cognitive performance in patients with morbid obesity before and after RYGB relative to lean controls.

METHODS AND ANALYSIS

This study is a pre-post case-control experiment. Using functional MRI, the neural responses to food stimuli and a working memory task will be compared between 25 patients with obesity, pre and post RYGB, and a matched, lean control group. Resting state fMRI will be measured to investigate functional brain connectivity. Baseline measurements for both groups will take place 4 weeks prior to RYGB and 12 months after RYGB. The effects of RYGB on peptide tyrosine tyrosine and glucagon-like polypeptide-1 will also be determined.

ETHICS AND DISSEMINATION

The project has received ethical approval by the local medical ethics committee of the Carl-von-Ossietzky University of Oldenburg, Germany (registration: 2017-073). Results will be published in a peer-reviewed journal as original research and on international conferences.

TRIAL REGISTRATION NUMBER

DRKS00012495; Pre-results.

Weight Loss Maintenance: Have We Missed the Brain?

Even though obese individuals often succeed with weight loss, long-term weight loss maintenance remains elusive. Dietary, lifestyle and psychosocial correlates of weight loss maintenance have been researched, yet the nature of maintenance is still poorly understood. Studying the neural processing of weight loss maintainers may provide a much-needed insight towards sustained obesity management. In this narrative review, we evaluate and critically discuss available evidence regarding the food-related neural responses of weight loss maintainers, as opposed to those of obese or lean persons. While research is still ongoing, available data indicate that following weight loss, maintainers exhibit persistent reward related feeling over food, similar to that of obese persons. However, unlike in obese persons, in maintainers, reward-related brain activity appears to be counteracted by subsequently heightened inhibition. These findings suggest that post-dieting, maintainers acquire a certain level of cognitive control which possibly protects them from weight regaining. The prefrontal cortex, as well as the limbic system, encompass key regions of interest for weight loss maintenance, and their contributions to long term successful weight loss should be further explored. Future possibilities and supportive theories are discussed.

Obesity, body weight regulation and the brain: insights from fMRI

Obesity constitutes a major global health threat. Despite the success of bariatric surgery in delivering sustainable weight loss and improvement in obesity-related morbidity, effective non-surgical treatments are urgently needed, necessitating an increased understanding of body weight regulation. Neuroimaging studies undertaken in people with healthy weight, overweight, obesity and following bariatric surgery have contributed to identifying the neurophysiological changes seen in obesity and help increase our understanding of the mechanisms driving the favourable eating behaviour changes and sustained weight loss engendered by bariatric surgery. These studies have revealed a key interplay between peripheral metabolic signals, homeostatic and hedonic brain regions and genetics. Findings from brain functional magnetic resonance imaging (fMRI) studies have consistently associated obesity with an increased motivational drive to eat, increased reward responses to food cues and impaired food-related self-control processes. Interestingly, new data link these obesity-associated changes with structural and connectivity changes within the central nervous system. Moreover, emerging data suggest that bariatric surgery leads to neuroplastic recovery. A greater understanding of the interactions between peripheral signals of energy balance, the neural substrates that regulate eating behaviour, the environment and genetics will be key for the development of novel therapeutic strategies for obesity. This review provides an overview of our current understanding of the pathoaetiology of obesity with a focus upon the role that fMRI studies have played in enhancing our understanding of the central regulation of eating behaviour and energy homeostasis.

Potential mechanisms underlying the effect of bariatric surgery on eating behaviour

PURPOSE OF REVIEW

Reduced energy intake, resulting from favourable changes in eating behaviour, is the predominant driver of weight loss following bariatric surgery. Here we review the most recent studies examining the impact of Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy, the two most common bariatric procedures, upon eating behaviour and the suggested underlying biological mechanisms.

RECENT FINDINGS

Following RYGB or sleeve gastrectomy, most people report subjective changes in appetite, taste and food preference, with decreased high-fat preference most commonly reported. Objective postsurgery changes in taste and olfactory acuity occur. A new phenomenon, 'meal-size aversion', may contribute to reduced postoperative energy intake. Recent studies provide evidence for peptide YY3-36, glucagon-like peptide-1, ghrelin, neurotensin and oleoylethanolamide as mediators of postoperative eating behaviour changes. Factors modulating these changes include sex, type 2 diabetes status, genetics and bariatric procedure. New studies implicate central dopaminergic and opioid receptor signalling as key neural mediators driving altered eating behaviour. Brain neuroimaging studies show that obesity-associated changes in food-cue responses, brain connectivity and structural abnormalities are normalized following bariatric surgery.

SUMMARY

Understanding the biological mechanisms mediating the eating behaviour changes engendered by bariatric surgery may lead to the development of novel therapeutic strategies for people with obesity.