Dietary Fat Modulation of Gut Microbiota and Impact on Regulatory Pathways Controlling Food Intake

Obesity is a multifactorial disease that continues to increase in prevalence worldwide. Emerging evidence has shown that the development of obesity may be influenced by taxonomic shifts in gut microbiota in response to the consumption of dietary fats. Further, these alterations in gut microbiota have been shown to promote important changes in satiation signals including gut hormones (leptin, ghrelin, GLP-1, peptide YY and CCK) and orexigenic and anorexigenic neuropeptides (AgRP, NPY, POMC, CART) that influence hyperphagia and therefore obesity. In this review, we highlight mechanisms by which gut microbiota can influence these satiation signals both locally in the gastrointestinal tract and via microbiota-gut-brain communication. Then, we describe the effects of dietary interventions and associated changes in gut microbiota on satiety signals through microbiota-dependent mechanisms. Lastly, we present microbiota optimizing therapies including prebiotics, probiotics, synbiotics and weight loss surgery that can help restore beneficial gut microbiota by enhancing satiety signals to reduce hyperphagia and subsequent obesity. Overall, a better understanding of the mechanisms by which dietary fats induce taxonomical shifts in gut microbiota and their impact on satiation signaling pathways will help develop more targeted therapeutic interventions in delaying the onset of obesity and in furthering its treatment.

Effect of bariatric surgery on maternal cardiovascular system

OBJECTIVE

Bariatric surgery is a successful treatment for sustainable weight loss and has been associated with improvement in cardiovascular function. Pregnancy after bariatric surgery is becoming increasingly common; however, little is known about the maternal cardiovascular system postsurgery. The aim of this study was to investigate maternal cardiovascular adaptation to pregnancy in women with previous bariatric surgery, compared with that in women with no history of weight-loss surgery and an early-pregnancy body mass index (BMI) similar to the presurgery BMI of the postbariatric women.

METHODS

This was a prospective, observational, longitudinal study conducted from April 2018 to June 2020 including 30 pregnant women who had undergone bariatric surgery and 30 who had not, matched for presurgery BMI. Participants were seen at three timepoints during pregnancy: 12-14, 20-24 and 30-32 weeks' gestation. At all visits, maternal blood pressure (BP) was measured and cardiac geometry and function were assessed using two-dimensional (2D) transthoracic echocardiography. On a subset of patients (15 in each group), 2D speckle tracking was performed to assess global longitudinal and circumferential strain. Offline analysis was performed, and multilevel linear mixed-effects models were used for all comparisons.

RESULTS

Compared with the no-surgery group, and across all trimesters, pregnant women with previous bariatric surgery had lower BP, heart rate and cardiac output and higher peripheral vascular resistance (P < 0.01 for all). Similarly, the postbariatric group demonstrated more favorable cardiac geometry and diastolic indices, including lower left ventricular mass, left atrial volume and relative wall thickness, together with higher E-wave/A-wave flow velocity across the mitral valve and higher mitral velocity (E') at the lateral and medial annulus on tissue Doppler imaging (P < 0.01 for all). There was no difference in ejection fraction, although global longitudinal strain was lower in postbariatric women (P < 0.01), indicating better systolic function.

CONCLUSION

Our findings indicate better maternal cardiovascular adaptation in women with previous bariatric surgery compared with presurgery BMI-matched pregnant women with no history of weight-loss surgery. © 2022 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

MTARC1 and HSD17B13 Variants Have Protective Effects on Non-Alcoholic Fatty Liver Disease in Patients Undergoing Bariatric Surgery

The severity of hepatic steatosis is modulated by genetic variants, such as patatin-like phospholipase domain containing 3 (PNPLA3) rs738409, transmembrane 6 superfamily member 2 (TM6SF2) rs58542926, and membrane-bound O-acyltransferase domain containing 7 (MBOAT7) rs641738. Recently, mitochondrial amidoxime reducing component 1 (MTARC1) rs2642438 and hydroxysteroid 17-beta dehydrogenase 13 (HSD17B13) rs72613567 polymorphisms were shown to have protective effects on liver diseases. Here, we evaluate these variants in patients undergoing bariatric surgery. A total of 165 patients who underwent laparoscopic sleeve gastrectomy and intraoperative liver biopsies and 314 controls were prospectively recruited. Genotyping was performed using TaqMan assays. Overall, 70.3% of operated patients presented with hepatic steatosis. NASH (non-alcoholic steatohepatitis) was detected in 28.5% of patients; none had cirrhosis. The increment of liver fibrosis stage was associated with decreasing frequency of the MTARC1 minor allele (p = 0.03). In multivariate analysis MTARC1 was an independent protective factor against fibrosis ≥ 1b (OR = 0.52, p = 0.03) and ≥ 1c (OR = 0.51, p = 0.04). The PNPLA3 risk allele was associated with increased hepatic steatosis, fibrosis, and NASH (OR = 2.22, p = 0.04). The HSD17B13 polymorphism was protective against liver injury as reflected by lower AST (p = 0.04) and ALT (p = 0.03) activities. The TM6SF2 polymorphism was associated with increased ALT (p = 0.04). In conclusion, hepatic steatosis is common among patients scheduled for bariatric surgery, but the MTARC1 and HSD17B13 polymorphisms lower liver injury in these individuals.

Risk of pre-eclampsia after gastric bypass: a matched cohort study

OBJECTIVE

To investigate whether gastric bypass before pregnancy is associated with reduced risk of pre-eclampsia.

DESIGN

Nationwide matched cohort study.

SETTING

Swedish national health care.

POPULATION

A total of 843 667 singleton pregnancies without pre-pregnancy hypertension were identified in the Swedish Medical Birth Register between 2007 and 2014, of which 2930 had a history of gastric bypass and a pre-surgery weight available from the Scandinavian Obesity Surgery Registry. Two matched control groups (pre-surgery and early-pregnancy body mass index [BMI]) were propensity score matched separately for nulliparous and parous births, to post-gastric bypass pregnancies (n_{pre-surgery-BMI}  = 2634:2634/n_{early-pregnancy-BMI}  = 2766:2766) on pre-surgery/early-pregnancy BMI, diabetes status (pre-surgery/pre-conception), maternal age, early-pregnancy smoking status, educational level, height, country of birth, delivery year and history of pre-eclampsia.

MAIN OUTCOME MEASURES

Pre-eclampsia categorised into any, preterm onset (<37⁺⁰  weeks) and term onset (≥37⁺⁰  weeks).

RESULTS

In post-gastric bypass pregnancies, mean pre-surgery BMI was 42.9 kg/m² and mean BMI loss between surgery and early pregnancy was 14.0 kg/m² (39 kg). Post-gastric bypass pregnancies had lower risk of pre-eclampsia compared with pre-surgery BMI-matched controls (1.7 versus 9.7 per 100 pregnancies; hazard ratio [HR] 0.21, 95% CI 0.15-0.28) and early-pregnancy BMI-matched controls (1.9 versus 5.0 per 100 pregnancies; HR 0.44, 95% CI 0.33-0.60). Although relative risks for pre-eclampsia for post-gastric bypass pregnancies versus pre-surgery matched controls was similar, absolute risk differences (RD) were significantly greater for nulliparous women (RD -13.6 per 100 pregnancies, 95% CI -16.1 to -11.2) versus parous women (RD -4.4 per 100 pregnancies, 95% CI -5.7 to -3.1).

CONCLUSION

We found that gastric bypass was associated with lower risk of pre-eclampsia, with the largest absolute risk reduction among nulliparous women.

TWEETABLE ABSTRACT

In this large study including two comparison groups matched for pre-surgery or early-pregnancy BMI, gastric bypass was associated with lower risk of pre-eclampsia.

'We Don't Want You to Diet': Bariatric professionals' boundary work and negotiation of pleasure and control

Although patients who undergo weight-loss surgery (WLS/bariatric surgery) must follow severe eating restrictions in a manner similar to that of dieting, professionals strive to demarcate distinctions between the approaches and methods of WLS and diet. Drawing from ethnographic research, this study focuses on the content and interpretative dimensions of professionals' boundary work as well as its meaning and implications for patients. The post-surgical body is revealed as a site of dispute. Professionals portray the logic of diet as one that assumes individuals ought to discipline themselves - and not 'give in' to pleasure - in order to achieve an ideal body. In contrast, WLS is depicted as a more advanced and balanced method that negotiates pleasure and control. Professionals construct boundaries by shifting the causes for obesity from the individual to the context, by expanding the meaning of success and by portraying food as healing. These findings join recent critical literature that shows that the lived experiences of care practices contest the prevailing framing of obesity care as solely about exerting disciplinary power and control. WLS professionals negotiate fat stigma and question dominant discourses regarding body size, thin ideals and responsibility.

Sick but healthy: bariatric patients and the social construction of illness and disability

Bariatric (weight loss) surgery modifies the digestive system, which produces impairments and symptoms which might be considered illness or disability. Bariatric patients, however, do not view themselves as ill or disabled, but healthier than before surgery. For this study, 35 bariatric patients - from a clinic located in the Midwestern United States - were interviewed to investigate how moral and medical discourses surrounding obesity impact how patients experience their bodies after bariatric surgery. While previous literature on bariatric patients has explored discourses of medicine, stigma and discipline, fewer have analysed how patients interpret physiological symptoms. Patients often reduce or discontinue medications for chronic illness after bariatric surgery, then replace them with a strict regimen of dietary supplements. Even though these supplements are taken to manage an impaired digestive system, they do not carry the same moral weight as medications for chronic illness. Patients also experience painful and humiliating symptoms after bariatric surgery. Bariatric patients interpret symptoms not as illness, but as important disciplinary tools to lose weight. These findings have implications for the social construction and experience of illness and disability in the context of fat stigma, health morality and biomedicalisation.

Vitamin K Status in Women of Childbearing Years Before or After Bariatric Surgery

BACKGROUND

Vitamin K adequacy has not been widely studied before or after bariatric surgery. Reports of babies born with intracranial bleeds to women after bariatric surgery make this an important vitamin to study in women of childbearing years.

OBJECTIVES

The aim of this study was to assess the functional vitamin K status in 2 groups of women of childbearing age, 1 group seeking bariatric surgery and 1 group post Roux-en-Y gastric bypass (RYGB).

METHODS

In a cross-sectional design, 40 women [19 presurgical and 21 post-RYGB (6-18 mo following surgery)], aged 18-40 y, completed the study. Participants provided a 3-d food intake record and a list of dietary supplements routinely taken. Participants then underwent a commercially available test to measure des-γ-carboxyprothrombin (DCP) concentration as a measure of functional vitamin K status.

RESULTS

Independent-samples t tests (P < 0.05) indicated that there was no significant difference [Sig (2-tailed) 0.821] between the DCP concentrations of the presurgical group and those of the post-RYGB group (mean ± SD DCP: 0.3 ± 0.1 and 0.4 ± 0.2 ng/mL, respectively). Vitamin K intake from food (248 ± 227 and 210 ± 239 μg) and supplements (13 ± 31 and 750 ± 271 μg) showed no linear correlation to DCP (presurgical group: 0.25 and -0.15, respectively; post-RYGB group: 0.13 and 0.05, respectively). Vitamin K intakes for both groups were above the current Institute of Medicine's recommended 90 μg/d for women. Bivariate correlation was conducted on other independent variables with only current BMI for the post-RYGB group having a moderate negative correlation to DCP (-0.54, P < 0.05). No correlation with statistical significance was found between other variables and DCP.

CONCLUSIONS

Although the American Society for Metabolic and Bariatric Surgery recommends DCP as a test to determine vitamin K adequacy, no published studies in pre- or post-RYGB patients have been performed with the current commercially available test, which is not FDA approved as a vitamin K biomarker. Previous studies reporting vitamin K inadequacies based on DCP utilized a different assay than the one currently available. Due to the importance of ensuring adequate maternal concentrations of vitamin K after bariatric surgery in order to prevent intracranial bleeding in babies, more research is needed to determine suitable vitamin K measures.

Tools for Successful Weight Management in Primary Care

Obesity is one of the most pervasive and costly public health problems. Clinicians need effective tools to address weight management in primary care, including evaluation and communication methods, guideline-based weight management interventions and safe and effective weight loss medications and surgery. The objective of this Grand Rounds presentation is to provide practicing clinicians with the latest information regarding effective ways to care for and communicate with patients about weight loss; evidence-based guidelines for selecting weight management therapies and safety, efficacy and adverse effects of weight loss medications and surgery.

Preoperative psychological assessment of patients seeking weight-loss surgery: identifying challenges and solutions

Preoperative psychosocial assessment is the standard of care for patients seeking weight-loss surgery (WLS). However, the assessment procedure varies widely by surgery site. Comprehensive assessments can provide a wealth of information that assists both the patient and the treatment team, anticipate and prepare for challenges associated with extensive behavioral and lifestyle changes that are required postsurgery. In this review, we provide an overview of the purpose of the preoperative psychosocial assessment and domains to be included. Challenges commonly identified in the assessment are discussed, including maladaptive eating behaviors, psychiatric comorbidities, and alcohol use. Potential solutions and approaches to these challenges are provided. Additionally, patient populations requiring special consideration are presented to include adolescents, those with cognitive vulnerabilities, and aging adults.

Weight-independent effects of roux-en-Y gastric bypass on glucose homeostasis via melanocortin-4 receptors in mice and humans

BACKGROUND & AIMS

Roux-en-Y gastric bypass (RYGB) improves glucose homeostasis independently of changes in body weight by unknown mechanisms. Melanocortin-4 receptors (MC4R) have weight-independent effects on glucose homeostasis, via autonomic neurons, and also might contribute to weight loss after RYGB. We investigated whether MC4Rs mediate effects of RYGB, such as its weight-independent effects on glucose homeostasis, in mice and humans.

METHODS

We studied C57BL/6 mice with diet-induced obesity, MC4R-deficient mice, and mice that re-express MC4R specifically in autonomic neurons after RYGB or sham surgeries. We also sequenced the MC4R locus in patients undergoing RYGB to investigate diabetes resolution in carriers of rare MC4R variants.

RESULTS

MC4Rs in autonomic brainstem neurons (including the parasympathetic dorsal motor vagus) mediated improved glucose homeostasis independent of changes in body weight. In contrast, MC4Rs in cholinergic preganglionic motor neurons (sympathetic and parasympathetic) mediated RYGB-induced increased energy expenditure and weight loss. Increased energy expenditure after RYGB is the predominant mechanism of weight loss and confers resistance to weight gain from a high-fat diet, the effects of which are MC4R-dependent. MC4R-dependent effects of RYGB still occurred in mice with Mc4r haplosufficiency, and early stage diabetes resolved at a similar rate in patients with rare variants of MC4R and noncarriers. However, carriers of MC4R (I251L), a rare variant associated with increased weight loss after RYGB and increased basal activity in vitro, were more likely to have early and weight-independent resolution of diabetes than noncarriers, indicating a role for MC4Rs in the effects of RYGB.

CONCLUSIONS

MC4Rs in autonomic neurons mediate beneficial effects of RYGB, including weight-independent improved glucose homeostasis, in mice and humans.

The effects of vertical sleeve gastrectomy in rodents are ghrelin independent

Reductions in levels of the hunger-stimulating hormone ghrelin have been proposed to mediate part of the effects of vertical sleeve gastrectomy (VSG) and Roux-en-Y gastric bypass surgeries for obesity. We studied circulating levels of acyl and desacyl ghrelin in rats after these surgeries. We found that blood levels of ghrelin were reduced after VSG, but not after Roux-en-Y gastric bypass, based on enzyme-linked immunosorbent assay and mass-spectrometry analyses. We compared the effects of VSG in ghrelin-deficient mice and wild-type mice on food intake, body weight, dietary fat preference, and glucose tolerance. We found that VSG produced comparable outcomes in each strain. Reduced ghrelin signaling therefore does not appear to be required for these effects of VSG.