Alterations in Fecal Short-Chain Fatty Acids after Bariatric Surgery: Relationship with Dietary Intake and Weight Loss

Gastrointestinal complaints after Roux-en-Y gastric bypass surgery. Impact of microbiota and its metabolites

Unexplainable gastrointestinal complaints occasionally occur after Roux-en-Y Gastric Bypass (RYGB) surgery. We therefor investigated the impact of microbiota composition and metabolites on gastrointestinal complaints after RYGB. In the BARICO study (Bariatric surgery Rijnstate and Radboudumc neuroimaging and Cognition in Obesity), microbiota and metabolites were measured before surgery, and 6, and 24 months after surgery. Gastrointestinal complaints were assessed with the Irritable Bowel Syndrome Severity Scoring System (IBS-SSS) questionnaire 24 months after surgery. 65 participants (86.2 % female) with a mean age of 46.2 ± 6.0 years, and mean BMI of 41.2 ± 3.6 kg/m2 were included. According to the IBS-SSS questionnaire, 32.3 % had moderate/severe gastrointestinal complaints 24 months after surgery. Microbiota alpha diversity remained stable, while beta diversity significantly changed over time. Bile acids and short-chain fatty acids were significantly higher, and inflammatory markers significantly lower after surgery. Barnesiella sp., Escherichia/Shigella sp., and Faecalibacterium prausnitzii correlated positively, while Akkermansia sp correlated inversely with gastrointestinal complaints. Patients with mild and moderate/severe gastrointestinal complaints showed higher levels of GLC-3S. These findings suggest involvement of microbiota and metabolite changes in gastrointestinal complaints after surgery. However, it remains unclear whether bacteria influence gastrointestinal complaints directly or indirectly. Further exploration is required for development of interventions against gastrointestinal symptoms after surgery.

Advancements in Understanding and Preventing Obesity-Related Colon Cancer

ABSTRACT

Obesity and colorectal cancer are global public health issues, with the prevalence of both conditions increasing over the last 4 decades. In the United States alone, the prevalence of obesity is greater than 40%, and this percentage is projected to increase past 50% by 2030. This review focuses on understanding the association between obesity and the risk of colorectal cancer while also highlighting hypotheses about molecular mechanisms underlying the link between these disease processes. We also consider whether those linkages can be disrupted via weight loss therapies, including lifestyle modifications, pharmacotherapy, bariatric surgery, and endobariatrics.

Influence of Bariatric Surgery on Gut Microbiota Composition and Its Implication on Brain and Peripheral Targets

Obesity remains a significant global health challenge, with bariatric surgery remaining as one of the most effective treatments for severe obesity and its related comorbidities. This review highlights the multifaceted impact of bariatric surgery beyond mere physical restriction or nutrient malabsorption, underscoring the importance of the gut microbiome and neurohormonal signals in mediating the profound effects on weight loss and behavior modification. The various bariatric surgery procedures, such as Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG), act through distinct mechanisms to alter the gut microbiome, subsequently impacting metabolic health, energy balance, and food reward behaviors. Emerging evidence has shown that bariatric surgery induces profound changes in the composition of the gut microbiome, notably altering the Firmicutes/Bacteroidetes ratio and enhancing populations of beneficial bacteria such as Akkermansia. These microbiota shifts have far-reaching effects beyond gut health, influencing dopamine-mediated reward pathways in the brain and modulating the secretion and action of key gut hormones including ghrelin, leptin, GLP-1, PYY, and CCK. The resultant changes in dopamine signaling and hormone levels contribute to reduced hedonic eating, enhanced satiety, and improved metabolic outcomes. Further, post-bariatric surgical effects on satiation targets are in part mediated by metabolic byproducts of gut microbiota like short-chain fatty acids (SCFAs) and bile acids, which play a pivotal role in modulating metabolism and energy expenditure and reducing obesity-associated inflammation, as well as influencing food reward pathways, potentially contributing to the regulation of body weight and reduction in hedonic eating behaviors. Overall, a better understanding of these mechanisms opens the door to developing non-surgical interventions that replicate the beneficial effects of bariatric surgery on the gut microbiome, dopamine signaling, and gut hormone regulation, offering new avenues for obesity treatment.

Effect of inulin on breath hydrogen, postprandial glycemia, gut hormone release, and appetite perception in RYGB patients: a prospective, randomized, cross-over pilot study

BACKGROUND AND OBJECTIVE

Large intestinal fermentation of dietary fiber may control meal-related glycemia and appetite via the production of short-chain fatty acids (SCFA) and the secretion of glucagon-like peptide-1 (GLP-1) and peptide YY (PYY). We investigated whether this mechanism contributes to the efficacy of the Roux-en-Y gastric bypass (RYGB) by assessing the effect of oligofructose-enriched inulin (inulin) vs. maltodextrin (MDX) on breath hydrogen (a marker of intestinal fermentation), plasma SCFAs, gut hormones, insulin and blood glucose concentrations as well as appetite in RYGB patients.

METHOD

Eight RYGB patients were studied on two occasions before and ~8 months after surgery using a cross-over design. Each patient received 300 ml orange juice containing 25 g inulin or an equicaloric load of 15.5 g MDX after an overnight fast followed by a fixed portion snack served 3 h postprandially. Blood samples were collected over 5 h and breath hydrogen measured as well as appetite assessed using visual analog scales.

RESULTS

Surgery increased postprandial secretion of GLP-1 and PYY (P ≤ 0.05); lowered blood glucose and plasma insulin increments (P ≤ 0.05) and reduced appetite ratings in response to both inulin and MDX. The effect of inulin on breath hydrogen was accelerated after surgery with an increase that was earlier in onset (2.5 h vs. 3 h, P ≤ 0.05), but less pronounced in magnitude. There was, however, no effect of inulin on plasma SCFAs or plasma GLP-1 and PYY after the snack at 3 h, neither before nor after surgery. Interestingly, inulin appeared to further potentiate the early-phase glucose-lowering and second-meal (3-5 h) appetite-suppressive effect of surgery with the latter showing a strong correlation with early-phase breath hydrogen concentrations.

CONCLUSION

RYGB surgery accelerates large intestinal fermentation of inulin, however, without measurable effects on plasma SCFAs or plasma GLP-1 and PYY. The glucose-lowering and appetite-suppressive effects of surgery appear to be potentiated with inulin.

Distinctive patterns of sulfide- and butyrate-metabolizing bacteria after bariatric surgery: potential implications for colorectal cancer risk

Despite improved cardiometabolic outcomes following bariatric surgery, its long-term impact on colorectal cancer (CRC) risk remains uncertain. In parallel, the influence of bariatric surgery on the host microbiome and relationships with disease outcomes is beginning to be appreciated. Therefore, we investigated the impact of Roux-en-Y gastric bypass (RYGB) and vertical sleeve gastrectomy (VSG) on the patterns of sulfide-reducing and butyrate-producing bacteria, which are hypothesized to modulate CRC risk after bariatric surgery. In this single-center, cross-sectional study, we included 15 pre-surgery subjects with severe obesity and patients who are at a median (range) of 25.6 (9.9-46.5) months after RYGB (n = 16) or VSG (n = 10). The DNA abundance of fecal bacteria and enzymes involved in butyrate and sulfide metabolism were identified using metagenomic sequencing. Differences between pre-surgery and post-RYGB or post-VSG cohorts were quantified using the linear discriminant analysis (LDA) effect size (LEfSe) method. Our sample was predominantly female (87%) with a median (range) age of 46 (23-71) years. Post-RYGB and post-VSG patients had a higher DNA abundance of fecal sulfide-reducing bacteria than pre-surgery controls (LDA = 1.3-4.4, p < .05). The most significant enrichments were for fecal E. coli, Acidaminococcus and A. finegoldii after RYGB, and for A. finegoldii, S. vestibularis, V. parvula after VSG. As for butyrate-producing bacteria, R. faecis was more abundant, whereas B. dentium and A. hardus were lower post-RYGB vs. pre-surgery. B. dentium was also lower in post-VSG vs. pre-surgery. Consistent with these findings, our analysis showed a greater enrichment of sulfide-reducing enzymes after bariatric surgery, especially RYGB, vs. pre-surgery. The DNA abundance of butyrate-producing enzymes was lower post-RYGB. In conclusion, the two most used bariatric surgeries, RYGB and VSG, are associated with microbiome patterns that are potentially implicated in CRC risk. Future studies are needed to validate and understand the impact of these microbiome changes on CRC risk after bariatric surgery.

Fecal short chain fatty acids modify therapeutic effects of sleeve gastrectomy

Aims

We aimed to investigate changes of fecal short chain fatty acids (SCFAs) and their association with metabolic benefits after sleeve gastrectomy (SG). Specifically, whether pre-surgery SCFAs modify surgical therapeutic effects was determined.

Methods

62 participants with measurements of fecal SCFAs and metabolic indices before and 1, 3, 6 months after SG were included. Changes of fecal SCFAs and their association with post-surgery metabolic benefits were calculated. Then, participants were stratified by medians of pre-surgery fecal SCFAs and modification effects of pre-surgery fecal SCFAs on surgical therapeutic effects were investigated, through calculating interaction of group by surgery.

Results

Fecal SCFAs were markedly changed by SG. Changes of propionate and acetate were positively correlated with serum triglycerides and total cholesterol, respectively. Notably, high pre-surgery fecal hexanoate group showed a better effect of SG treatment on lowering body weight (P=0.01), BMI (P=0.041) and serum triglycerides (P=0.031), and low pre-surgery fecal butyrate had a better effect of SG on lowering ALT (P=0.003) and AST (P=0.019).

Conclusion

Fecal SCFAs were changed and correlated with lipid profiles improvement after SG. Pre-surgery fecal hexanoate and butyrate were potential modifiers impacting metabolic benefits of SG.

The Risk of Colorectal Polyps after Weight Loss Therapy Versus Obesity: A Propensity-Matched Nationwide Cohort Study

BACKGROUND

A fundamental understanding of the impact of bariatric surgery (BRS) on mechanisms of colorectal carcinogenesis is limited. For instance, studies report a reduced risk of colorectal cancer in females but not in males after BRS. We examined whether this sex-specific difference existed at the earlier polyp development stage.

METHODS

This retrospective cohort study included 281,417 adults from the 2012-2020 MarketScan database. We compared polyps rates on colonoscopy in four groups: post- vs. pre-BRS (treatment) to post- vs. pre-severe obesity (SO) diagnosis (control). We focused our main analysis on a propensity-matched sample that yielded a balanced distribution of covariates in our four groups (n = 9680 adults, 21.9% males). We also adjusted for important covariates.

RESULTS

Metabolic syndrome parameters improved after bariatric surgery and worsened after severe obesity diagnosis (p < 0.05). The rate of polyps was 46.7% at a median of 0.5 years pre-BRS and 47.9% at a median of 0.6 years pre-SO diagnosis. The polyps rate was 45.4% at a median (range) of 3.2 (1.0-8.5) years post-BRS. Conversely, 53.8% of adults had polyps at 3.0 (1.0-8.6) years post-SO. There was no change in the risk of colorectal polyps in males or females post- vs. pre-BRS. However, the risk of polyps was higher in males (OR = 1.32, 95% CI: 1.02-1.70) and females (OR = 1.29, 95% CI: 1.13-1.47) post- vs. pre-SO. When compared to the control group (SO), the odds ratios for colorectal polyps were lower for males and females after bariatric surgery (OR = 0.63, 95% CI: 0.44-0.90, and OR = 0.79, 95% CI: 0.66-0.96, respectively).

CONCLUSIONS

Obesity is associated with an increased risk of colorectal polyps, an effect that is ameliorated after bariatric surgery. These data are relevant for studies investigating colorectal carcinogenesis mechanisms.

An Imbalance of Pathophysiologic Factors in Late Postprandial Hypoglycemia Post Bariatric Surgery: A Narrative Review

With a rise in obesity and more patients opting for bariatric surgery, it becomes crucial to understand associated complications like postprandial hypoglycemia (PPH). After bariatric surgery, significant changes are seen in insulin sensitivity, beta cell function, glucagon-like peptide 1 (GLP-1) levels, the gut microbiome, and bile acid metabolism. And in a small subset of patients, exaggerated imbalances in these functional and metabolic processes lead to insulin-glucose mismatch and hypoglycemia. The main treatment for PPH involves dietary modifications. For those that do not respond, medications or surgical interventions are considered to reverse some of the imbalances. We present a few case reports of patients that safely tolerated GLP-1 agonists. However, larger randomized control trials are needed to further characterize PPH and understand its treatment.

Short-Chain Fatty Acids-A Product of the Microbiome and Its Participation in Two-Way Communication on the Microbiome-Host Mammal Line

PURPOSE OF REVIEW

The review aims to describe short-chain fatty acids (SCFAs) as metabolites of bacteria, their complex influence on whole-body metabolism, and alterations in the SCFA profile in obesity and after bariatric surgery (BS).

RECENT FINDINGS

The fecal profile of SCFAs in obese patients differs from that of lean patients, as well as their gut microbiota composition. In obese patients, a lower diversity of bacteria is observed, as well as higher concentrations of SCFAs in stool samples. Obesity is now considered a global epidemic and bariatric surgery (BS) is an effective treatment for severe obesity. BS affects the structure and functioning of the digestive system, and also alters gut microbiota and the concentration of fecal SCFAs. Generally, after BS, SCFA levels are lower but levels of branched short-chain fatty acids (BSCFAs) are elevated, the effect of which is not fully understood. Moreover, changes in the profile of circulating SCFAs are little known and this is an area for further research. Obesity seems to be inherently associated with changes in the SCFA profile. It is necessary to better understand the impact of BS on microbiota and the metabolome in both feces and blood as only a small percentage of SCFAs are excreted. Further research may allow the development of a personalized therapeutic approach to the BS patient in terms of diet and prebiotic intervention.

The impact of microbially modified metabolites associated with obesity and bariatric surgery on antitumor immunity

Obesity is strongly associated with the occurrence and development of many types of cancers. Patients with obesity and cancer present with features of a disordered gut microbiota and metabolism, which may inhibit the physiological immune response to tumors and possibly damage immune cells in the tumor microenvironment. In recent years, bariatric surgery has become increasingly common and is recognized as an effective strategy for long-term weight loss; furthermore, bariatric surgery can induce favorable changes in the gut microbiota. Some studies have found that microbial metabolites, such as short-chain fatty acids (SCFAs), inosine bile acids and spermidine, play an important role in anticancer immunity. In this review, we describe the changes in microbial metabolites initiated by bariatric surgery and discuss the effects of these metabolites on anticancer immunity. This review attempts to clarify the relationship between alterations in microbial metabolites due to bariatric surgery and the effectiveness of cancer treatment. Furthermore, this review seeks to provide strategies for the development of microbial metabolites mimicking the benefits of bariatric surgery with the aim of improving therapeutic outcomes in cancer patients who have not received bariatric surgery.

Correlations between the Changing Levels of Tissue Plasminogen Activator and Adiposity Following Exercise-Induced Weight Loss

Cardiovascular disease is a major threat to global public health. Tissue plasminogen activator (TPA) is a serine protease that dissolves blood clots, which can also lead to excessive bleeding. Fibrinogen (FIBR), a glycoprotein, is converted by thrombin to fibrin and then to a fibrin-based blood clot. Both TPA and FIBR levels in the blood are associated with an increased risk of coronary heart disease, and the levels of the two factors are also positively correlated with total adipose tissue amounts. Visceral and subcutaneous adipose tissues (VAT and SAT) can contribute differently to whole-body metabolism. In this study, we sought to assess: (1) the strength of the correlation between the changing levels of the two factors and the changing amounts of VAT/SAT during exercise-induced weight loss, (2) whether there is any difference between the two types of adipose tissues in terms of the correlation, and (3) which factor, TPA or FIBR, is more sensitive to changes in adiposity? For this study, we analyzed the data from the diabetes prevention program (DPP), in which the participants were divided into three groups, with one group undergoing a lifestyle change that involved maintaining a minimum of 7% weight loss with physical activity. We found that the basal amounts of VAT and SAT were correlated with TPA and FIBR levels. However, following weight loss, adiposity changes were strongly correlated with the changing levels of TPA, but not FIBR, for both men and women. Therefore, TPA, but not FIBR, is sensitive to changes in adiposity. Furthermore, regarding TPA, weight loss sensitized its correlation with SAT, but not VAT. This study shows how adipose tissues distinctively affect TPA and FIBR levels, two factors associated with cardiovascular disease and ischemic stroke.