Coffee, Alcohol, and Artificial Sweeteners Have Temporal Associations with Gastrointestinal Symptoms

BACKGROUND

Various dietary strategies for managing irritable bowel syndrome (IBS) target mechanisms such as brain-gut interactions, osmotic actions, microbial gas production, and local immune activity. These pathophysiological mechanisms are diverse, making it unclear which foods trigger IBS symptoms for a substantial proportion of patients.

AIM

To identify associations between foods and gastrointestinal symptoms.

METHODS

From the mySymptoms smartphone app, we collected anonymized diaries of food intake and symptoms (abdominal pain, diarrhea, bloating, and gas). We selected diaries that were at least 3 weeks long. The diaries were analyzed for food-symptom associations using a proprietary algorithm. As the participants were anonymous, we conducted an app-wide user survey to identify IBS diagnoses according to Rome IV criteria.

RESULTS

A total of 9,710 food symptom diaries that met the quality criteria were collected. Of the survey respondents, 70% had IBS according to Rome IV criteria. Generally, strong associations existed for caffeinated coffee (diarrhea, 1-2 h postprandial), alcoholic beverages (multiple symptoms, 4-72 h postprandial), and artificial sweeteners (multiple symptoms, 24-72 h postprandial). Histamine-rich food intake was associated with abdominal pain and diarrhea. Some associations are in line with existing literature, whilst the absence of an enriched FODMAP-symptom association contrasts with current knowledge.

CONCLUSIONS

Coffee, alcohol, and artificial sweeteners were associated with GI symptoms in this large IBS-predominant sample. Symptom onset is often within 2 h postprandial, but some foods were associated with a delayed response, possibly an important consideration in implementing dietary recommendations. Clinical trials must test the causality of the demonstrated food-symptom associations.

Colonic butyrate administration modulates fear memory but not the acute stress response in men: A randomized, triple-blind, placebo-controlled trial

Short-chain fatty acids (SCFAs) are produced in the colon following bacterial fermentation of dietary fiber and are important microbiota-gut-brain messengers. However, their mechanistic role in modulating psychobiological processes that underlie the development of stress- and anxiety-related disorders is scarcely studied in humans. We have previously shown that colonic administration of a SCFA mixture (acetate, propionate, butyrate) lowers the cortisol response to stress in healthy participants, but does not impact fear conditioning and extinction. To disentangle the effects of the three main SCFAs, we examined whether butyrate alone would similarly modulate these psychobiological responses in a randomized, triple-blind, placebo-controlled intervention study in 71 healthy male participants (Mage = 25.2, MBMI = 22.7 [n = 35 butyrate group, n = 36 placebo group]). Colon-delivery capsules with pH-dependent coating were used to administer 5.28 g of butyrate or placebo daily for one week. Butyrate administration significantly increased serum butyrate concentrations without modulating serum acetate or propionate, nor fecal SCFAs. Butyrate administration also significantly modulated fear memory at the subjective but not physiological levels. Contrary to expectations, no changes in subjective nor neuroendocrine responses to acute stress were evident between the treatment groups from pre- to post-intervention. We conclude that colonic butyrate administration alone is not sufficient to modulate psychobiological stress responses, unlike administration of a SCFA mixture. The influence of colonic and systemic butyrate on fear memory and the persistence of fear extinction should be further systematically investigated in future studies.

The Leuven Prolonged Acute Stress Test (L-PAST): A novel paradigm to induce a subjective and glucocorticoid stress response for at least ninety minutes

Laboratory stress tests typically administer stress acutely, ranging from 3 to 15 minutes. However, everyday stressors usually last longer than ten minutes (e.g., examination stressors, work stressors, and social stressors. Moreover, in some studies, it may be relevant to induce stress for a longer period to affect certain psychological or physiological parameters. To this end, we developed a novel stress test that intends to induce psychosocial stress for 90 minutes. The Leuven Prolonged Acute Stress Test (L-PAST) combines physical (hand immersion in cold water), cognitive (mental arithmetic), and psychosocial (social evaluation and feelings of failure) stress elements of two well-known laboratory stress tests, the Maastricht Acute Stress Test (MAST) and the Montreal Imaging Stress Test (MIST). Fifty healthy women were subjected to both the L-PAST and a sham (control) test in a randomized and counterbalanced manner. The stress response was determined by salivary cortisol measurements and assessment of subjective stress ratings at regular time points during the time preceding the stress period (5 min), the stress period (90 min), and the recovery period (35 min). Cognitive reactivity to failure and subjective pain levels were also assessed at various time points. The childhood trauma questionnaire (CTQ) and the perceived stress scale (PSS) were administered prior to the testing phase. As expected, linear mixed models revealed that the stress response was significantly higher during the L-PAST as indicated by a significant time point by condition interaction effect for both the cortisol response (F(10,450)=12.21, p < 0.0001, ηp2=0.11) and the subjective stress response (F(13,637)=13.98, p < 0.0001, ηp2 = 0.12). Moreover, there was a significant time point by condition interaction effect for cognitive reactivity to failure (F(13,637) = 7.97, p < 0.0001, ηp2 = 0.07) and subjective pain (F(13,637) = 38.52, p < 0.0001, ηp2 = 0.27), indicating that the levels were higher during the L-PAST at most stress induction time points. Lastly, higher CTQ scores were associated with higher subjective pain levels during the L-PAST (F(1,44)=6.05, p = 0.02). Collectively, our results confirm the efficacy of the L-PAST in inducing a prolonged subjective as well as cortisol stress response.

Do we perceive sensations inside and outside of our body differently? Perceptual, emotional, and behavioral differences between visceral and somatic sensation, discomfort, and pain

BACKGROUND

Experimental research evaluating differences between the visceral and somatic stimulation is limited to pain and typically uses different induction methods for visceral and somatic stimulation (e.g., rectal balloon distention vs. tactile hand stimulation). Our study aimed to compare differences in response time, intensity, unpleasantness, and threat between identical electrical visceral and somatic stimulations at both painful and non-painful perceptual thresholds.

METHODS

Electrical stimulation was applied to the wrist and distal esophagus in 20 healthy participants. A double pseudorandom staircase determined perceptual thresholds of Sensation, Discomfort, and Pain for the somatic and visceral stimulations, separately. Stimulus reaction time (ms, via button press), and intensity, unpleasantness, and threat ratings were recorded after each stimulus. General linear mixed models compared differences in the four outcomes by stimulation type, threshold, and the stimulation type-by-threshold interaction. Sigmoidal maximum effect models evaluated differences in outcomes across all delivered stimulation intensities.

KEY RESULTS

Overall, visceral stimulations were perceived as more intense, threatening, and unpleasant compared to somatic stimulations, but participants responded faster to somatic stimulations. There was no significant interaction effect, but planned contrasts demonstrated differences at individual thresholds. Across all delivered intensities, higher intensity stimulations were needed to reach the half-maximum effect of self-reported intensity, unpleasantness, and threat ratings in the visceral domain.

CONCLUSIONS AND INFERENCES

Differences exist between modalities for both non-painful and painful sensations. These findings may have implications for translating paradigms and behavioral treatments from the somatic domain to the visceral domain, though future research in larger clinical samples is needed.

Poor Subjective Sleep Quality Predicts Symptoms in Irritable Bowel Syndrome Using the Experience Sampling Method

INTRODUCTION

Sleep quality may affect symptom experience in irritable bowel syndrome (IBS). Our aim was to investigate the relationship between sleep quality and gastrointestinal (GI) symptoms using actigraphy and the experience sampling method.

METHODS

Patients with IBS were recruited from a tertiary Neurogastroenterology clinic and the community. GI symptoms and mood were recorded on a smartphone application, 10 times per day, over 7 consecutive days. Subjective sleep quality was recorded every morning to reflect the night before. Objective measures of sleep quality were estimated from wrist-worn actigraphy. Cross-lagged structural equation models were built to assess the directionality of sleep-symptom relationships over time.

RESULTS

Eighty patients with IBS completed the study (mean age: 37 years [range 20-68], 89% female, 78% community). Approximately 66% had a Pittsburgh Sleep Quality Index score ≥ 8, indicating a clinically significant sleep disturbance. Approximately 82% (95% CI: 72-90) screened positive for a sleep disorder, most commonly insomnia. In cross-lagged analysis, poor subjective sleep quality predicted next-day abdominal pain (0.036 < P < 0.040) and lower GI symptoms (0.030 < P < 0.032), but not vice versa. No significant relationship with GI symptoms was found for any objective sleep measure using actigraphy.

DISCUSSION

Poor subjective sleep quality was associated with higher next-day lower GI symptom levels, but not vice versa. Objective sleep measures did not predict next-day abdominal symptoms, potentially supporting the conclusion that it is the perception of sleep quality that is most influential. This study may be used to guide future research into the effect of sleep interventions on GI symptoms.

Brief cognitive-behavioral treatment for avoidant/restrictive food intake disorder in the context of functional dyspepsia: Study protocol for a feasibility randomized controlled trial

BACKGROUND

Avoidant/restrictive food intake disorder (ARFID) symptoms are common (up to 40%) among adults with functional dyspepsia (FD), a disorder of gut-brain interaction characterized by early satiation, post-prandial fullness, epigastric pain, and/or epigastric burning. Using an 8-session exposure-based cognitive-behavioral treatment (CBT) for adults with FD + ARFID compared to usual care (UC) alone, we aim to: (1) determine feasibility, (2) evaluate change in clinical outcomes in, and (3) explore possible mechanisms of action.

METHODS

We will randomize adults with FD who meet criteria for ARFID with ≥5% weight loss (N = 50) in a 1:1 ratio to CBT (with continued UC) or to UC alone. A priori primary benchmarks will be: ≥75% eligible participants enroll; ≥75% participants complete assessments; ≥70% participants attend 6/8 sessions; ≥70% of sessions have all content delivered; ≥70% participants rate Client Satisfaction Questionnaire scores above scale midpoint. We will also examine the size of changes in FD symptom severity and related quality of life within and between groups, and explore possible mechanisms of action.

CONCLUSIONS

Findings from this trial will inform next steps with treatment development or evaluation-either for further refinement or for next-step efficacy testing with a fully-powered clinical trial.

Psychosocial stress-induced intestinal permeability in healthy humans: What is the evidence?

An impaired intestinal barrier function can be detrimental to the host as it may allow the translocation of luminal antigens and toxins into the subepithelial tissue and bloodstream. In turn, this may cause local and systemic immune responses and lead to the development of pathologies. In vitro and animal studies strongly suggest that psychosocial stress is one of the factors that can increase intestinal permeability via mast-cell dependent mechanisms. Remarkably, studies have not been able to yield unequivocal evidence that such relation between stress and intestinal permeability also exists in (healthy) humans. In the current Review, we discuss the mechanisms that are involved in stress-induced intestinal permeability changes and postulate factors that influence these alterations and that may explain the translational difficulties from in vitro and animal to human studies. As human research differs highly from animal research in the extent to which stress can be applied and intestinal permeability can be measured, it remains difficult to draw conclusions about the presence of a relation between stress and intestinal permeability in (healthy) humans. Future studies should bear in mind these difficulties, and more research into in vivo methods to assess intestinal permeability are warranted.

The role of short-chain fatty acids (SCFAs) in regulating stress responses, eating behavior, and nutritional state in anorexia nervosa: protocol for a randomized controlled trial

OBJECTIVE

This protocol proposes investigating the effects of short-chain fatty acids (SCFAs)-namely acetate, propionate, and butyrate-as mediators of microbiota-gut-brain interactions on the acute stress response, eating behavior, and nutritional state in malnourished patients with anorexia nervosa (AN). SCFAs are produced by bacterial fermentation of dietary fiber in the gut and have recently been proposed as crucial mediators of the gut microbiota's effects on the host. Emerging evidence suggests that SCFAs impact human psychobiology through endocrine, neural, and immune pathways and may regulate stress responses and eating behavior.

METHOD

We will conduct a randomized, triple-blind, placebo-controlled trial in 92 patients with AN. Patients will receive either a placebo or a mixture of SCFAs (acetate propionate, butyrate) using pH-dependent colon-delivery capsules for six weeks. This clinical trial is an add-on to the standard inpatient psychotherapeutic program focusing on nutritional rehabilitation.

HYPOTHESES

We hypothesize that colonic SCFAs delivery will modulate neuroendocrine, cardiovascular, and subjective responses to an acute laboratory psychosocial stress task. As secondary outcome measures, we will assess alterations in restrictive eating behavior and nutritional status, as reflected by changes in body mass index. Additionally, we will explore changes in microbiota composition, gastrointestinal symptoms, eating disorder psychopathology, and related comorbidities.

DISCUSSION

The findings of this study would enhance our understanding of how gut microbiota-affiliated metabolites, particularly SCFAs, impact the stress response and eating behavior of individuals with AN. It has the potential to provide essential insights into the complex interplay between the gut, stress system, and eating behavior and facilitate new therapeutic targets for stress-related psychiatric disorders. This protocol is prospectively registered with ClinicalTrials.gov, with trial registration number NCT06064201.

Psychological Processes, Not Physiological Parameters, Are Most Important Contributors to Symptom Severity in Patients With Refractory Heartburn/Regurgitation Symptoms

BACKGROUND & AIMS

Physiological and psychological factors have been found to influence esophageal symptom reporting. We aimed to evaluate which of these factors are associated with 3 reflux symptom severity outcomes (ie, Total Reflux, Heartburn, and Sleep Disturbance) through a traditional statistical and a complementary machine-learning approach.

METHODS

Consecutive adult patients with refractory heartburn/regurgitation symptoms underwent standard 24-hour pH-impedance monitoring and completed questionnaires assessing past and current gastrointestinal and psychological health. In the traditional statistical approach, hierarchical general linear models assessed relationships of psychological and physiological variables (eg, total number of reflux episodes) with reflux severity scores. Mediation analyses further assessed pathways between relevant variables. In the machine-learning approach, all psychological and physiological variables were entered into 11 different models and cross-validated model performance was compared among the different models to select the best model.

RESULTS

Three hundred ninety-three participants (mean [SD] age, 48.5 [14.1] years; 60% were female) were included. General psychological functioning emerged as an important variable in the traditional statistical approach, as it was significantly associated with all 3 outcomes and mediated the relationship between childhood trauma and both Total Reflux and Heartburn Severity. In the machine-learning analyses, general psychological variables (eg, depressive symptoms) were most important for Total Reflux and Sleep Disturbance outcomes, and symptom-specific variables, like visceral anxiety, were more influential for Heartburn Severity. Physiological variables were not significant contributors to reflux symptom severity outcomes in our sample across reflux classifications and statistical methodology.

CONCLUSIONS

Psychological processes, both general and symptom-specific, should be considered as another important factor within the multifactorial processes that impact reflux symptom severity reporting across the reflux spectrum.

Genetic risk shared across 24 chronic pain conditions: identification and characterization with genomic structural equation modeling

ABSTRACT

Chronic pain conditions frequently co-occur, suggesting common risks and paths to prevention and treatment. Previous studies have reported genetic correlations among specific groups of pain conditions and reported genetic risk for within-individual multisite pain counts (≤7). Here, we identified genetic risk for multiple distinct pain disorders across individuals using 24 chronic pain conditions and genomic structural equation modeling (Genomic SEM). First, we ran individual genome-wide association studies (GWASs) on all 24 conditions in the UK Biobank ( N ≤ 436,000) and estimated their pairwise genetic correlations. Then we used these correlations to model their genetic factor structure in Genomic SEM, using both hypothesis- and data-driven exploratory approaches. A complementary network analysis enabled us to visualize these genetic relationships in an unstructured manner. Genomic SEM analysis revealed a general factor explaining most of the shared genetic variance across all pain conditions and a second, more specific factor explaining genetic covariance across musculoskeletal pain conditions. Network analysis revealed a large cluster of conditions and identified arthropathic, back, and neck pain as potential hubs for cross-condition chronic pain. Additionally, we ran GWASs on both factors extracted in Genomic SEM and annotated them functionally. Annotation identified pathways associated with organogenesis, metabolism, transcription, and DNA repair, with overrepresentation of strongly associated genes exclusively in brain tissues. Cross-reference with previous GWASs showed genetic overlap with cognition, mood, and brain structure. These results identify common genetic risks and suggest neurobiological and psychosocial mechanisms that should be targeted to prevent and treat cross-condition chronic pain.

Psychological symptoms do not discriminate between reflux phenotypes along the organic-functional refractory GERD spectrum

OBJECTIVE

Historically, psychological processes are associated with disorders at the functional end of the gastro-oesophageal reflux disease (GERD) spectrum. However, recent research suggests that psychological symptoms are relevant across the entire GERD spectrum. We aim to investigate whether psychological symptoms are associated with reflux phenotype (True GERD, Borderline GERD, reflux hypersensitivity, functional heartburn) along the GERD spectrum in a cohort of refractory reflux patients.

DESIGN

Consecutive adult patients with refractory reflux symptoms underwent standard 24-hour pH-impedance monitoring and completed questionnaires assessing demographic, clinical and psychological information. Bayesian one-way analysis of variance assessed whether psychological variables differed across reflux phenotypes. Next, we applied multinomial and ordinal logistic regressions with clinical, demographic and psychological variables set as independent variables and reflux phenotype as the outcome variable. The complementary machine-learning approach entered all demographic, clinical and psychological variables into models, with reflux phenotype set nominally and ordinally. Cross-validated model performance was used to select the best model.

RESULTS

393 participants (mean (SD) age=48.5 (14.1); 60% female) were included. The Bayesian analyses found no difference in psychological variables across reflux phenotypes. Similarly, age, gender and proton pump inhibitor use were the only significant variables in the multinomial logistic regression and body mass index was significant in both regressions. Machine-learning analyses revealed poorly performing models with high misclassification rates (67-68%) in both models.

CONCLUSION

Psychological symptoms do not differ between nor predict reflux phenotype membership in refractory reflux patients. Findings suggest that psychological symptoms are relevant across the spectrum of GERD, rather than specific to functional oesophageal disorders.

A novel self-report scale of interoception: the three-domain interoceptive sensations questionnaire (THISQ)

OBJECTIVES

The self-reported perception of bodily sensations is assumed predictive for health and disease. Existing questionnaires mostly focus on aversive sensations, and associated emotions and cognitions, which potentially confounds associations between interoception and illness. Therefore, we developed the Three-domain Interoceptive Sensations Questionnaire (THISQ), assessing self-reported perception of neutral respiratory, cardiac, and gastroesophageal sensations.

DESIGN

Using cross-sectional surveys, we developed and validated the THISQ.

MAIN OUTCOME MEASURES

In Sample 1 (n = 357), a pool of 28 Dutch items was subjected to exploratory factor analysis. Eighteen items with a primary factor loading >.40 were retained for confirmatory factor analysis in Sample 2 (n = 374) and Sample 3 (n = 484) for the validation of the Dutch and English questionnaire, respectively.

RESULTS

Analyses supported the 3-factor solution: cardiorespiratory activation, cardiorespiratory deactivation, and gastroesophageal sensations. Scales showed acceptable to good internal consistency. Convergent validity was confirmed by significant medium associations between THISQ scores and other self-report measures of interoception. Divergent validity was supported by non-significant or small associations with measures of negative affectivity and symptom-related anxiety.

CONCLUSION

Our findings suggest that the Dutch and English THISQs are valid and reliable self-report measures of interoception, which could advance our understanding of interoceptive processes in health and disease.

Supplemental data for this article is available online at https://doi.org/10.1080/08870446.2021.2009479 .

Brain mediators of negative affect-induced physical symptom reporting in patients with functional somatic syndromes

Functional somatic syndromes (FSS) include fibromyalgia, irritable bowel syndrome (IBS), and others. In FSS patients, merely viewing negative affective pictures can elicit increased physical symptoms. Our aim was to investigate the neural mechanisms underlying such negative affect-induced physical symptoms in FSS patients. Thirty patients with fibromyalgia and/or IBS and 30 healthy controls (all women) watched neutral, positive and negative affective picture blocks during functional MRI scanning and rated negative affect and physical symptoms after every block. We compared brain-wide activation during negative versus neutral picture viewing in FSS patients versus controls using robust general linear model analysis. Further, we compared neurologic pain signature (NPS), stimulus intensity-independent pain signature (SIIPS) and picture-induced negative emotion signature (PINES) responses to the negative versus neutral affect contrast and investigated whether they mediated between-group differences in affective picture-induced physical symptom reporting. More physical symptoms were reported after viewing negative compared to neutral pictures, and this effect was larger in patients than controls (p = 0.025). Accordingly, patients showed stronger activation in somatosensory regions during negative versus neutral picture viewing. NPS, but not SIIPS nor PINES, responses were higher in patients than controls during negative versus neutral pictures (p = 0.026). These differential NPS responses partially mediated between-group differences in physical symptoms. In conclusion, picture-induced negative affect elicits physical symptoms in FSS patients as a result of activation of somatosensory and nociceptive brain patterns, supporting the idea that affect-driven alterations in processing of somatic signals is a critical mechanism underlying FSS.

Bifidobacterium longum subsp. longum Reduces Perceived Psychological Stress in Healthy Adults: An Exploratory Clinical Trial

Emerging science shows that probiotic intake may impact stress and mental health. We investigated the effect of a 6-week intervention with Bifidobacterium longum (BL) NCC3001 (1 × 10¹⁰ CFU/daily) on stress-related psychological and physiological parameters in 45 healthy adults with mild-to-moderate stress using a randomized, placebo-controlled, two-arm, parallel, double-blind design. The main results showed that supplementation with the probiotic significantly reduced the perceived stress and improved the subjective sleep quality score compared to placebo. Comparing the two groups, momentary subjective assessments concomitant to the Maastricht Acute Stress Test revealed a lower amount of pain experience in the probiotic group and a higher amount of relief at the end of the procedure in the placebo group, reflected by higher scores in the positive affect state. The awakening of the salivary cortisol response was not affected by the intervention, yet the reduction observed in the salivary cortisol stress response post-intervention was higher in the placebo group than the probiotic group. Multivariate analysis further indicated that a reduction in perceived stress correlated with a reduction in anxiety, in depression, and in the cortisol awakening response after the 6-week intervention. This exploratory trial provides promising insights into BL NCC3001 to reduce perceived stress in a healthy population and supports the potential of nutritional solutions including probiotics to improve mental health.

Personal identity, somatic symptoms, and symptom-related thoughts, feelings, and behaviors in adolescence: Examining between- and within-person associations and the role of depressive symptoms

Recent literature highlights the complex relationship between personal identity and body-related pathology, yet there is a lack of integrative longitudinal research on the relationship between identity and somatic symptoms. The present study investigated the longitudinal associations between identity functioning and (psychological characteristics of) somatic symptoms, and examined the role of depressive symptoms in this relationship. A total of 599 community adolescents (Time 1: 41.3% female; M_age = 14.93, SD = 1.77, range = 12-18 years) participated in three annual assessments. Using cross-lagged panel models, a bidirectional relationship between identity and (psychological characteristics of) somatic symptoms, mediated by depressive symptoms, emerged at the between-person level; whereas only a unidirectional relationship from psychological characteristics of somatic symptoms to identity functioning, mediated by depressive symptoms, emerged at the within-person level. Identity and depressive symptoms were bidirectionally related at both levels. The present study suggests that adolescent identity development is closely related to somatic and emotional distress.

Illness Identity in Inflammatory Bowel Disease

BACKGROUND

We examined the degree to which adults with inflammatory bowel disease (IBD) integrated their illness into their identity and linked illness identity to important patient-reported outcomes.

METHODS

A total of 109 adults with IBD, aged 18 to 60 (M_age = 35.93; 77% women) completed questionnaires on the four illness identity dimensions (rejection, acceptance, engulfment, and enrichment), medication adherence, depressive symptoms, life satisfaction, health status, and health-related quality of life (HRQoL). The illness identity scores of adults with IBD were compared to existing data from adults with congenital heart disease (CHD), refractory epilepsy (RE), and multisystemic connective tissue disorders (MSDs) using multivariate analyses of covariance. In adults with IBD, associations between illness identity and patient-reported outcomes were examined through hierarchical regression analyses, controlling for sex, age, illness duration, diagnosis, self-reported flares, and co-existing illnesses.

RESULTS

Adults with IBD scored higher on rejection and engulfment and lower on acceptance than adults with CHD, lower on rejection but higher on engulfment than adults with RE, and higher on engulfment and enrichment but lower on rejection than adults with MSDs. Higher engulfment scores were related to more depressive symptoms, lower life satisfaction, and a poorer health status and HRQoL. In contrast, higher enrichment scores were related to more life satisfaction and a better HRQoL. Rejection and acceptance were not uniquely related to any of the outcomes.

CONCLUSIONS

Adults with IBD showed relatively high levels of engulfment. Substantial associations were observed between illness identity and patient-reported outcomes, with engulfment being the strongest, most consistent predictor.

The neurobiological basis of affect is consistent with psychological construction theory and shares a common neural basis across emotional categories

Affective experience colours everyday perception and cognition, yet its fundamental and neurobiological basis is poorly understood. The current debate essentially centers around the communalities and specificities across individuals, events, and emotional categories like anger, sadness, and happiness. Using fMRI during the experience of these emotions, we critically compare the two dominant conflicting theories on human affect. Basic emotion theory posits emotions as discrete universal entities generated by dedicated emotion category-specific neural circuits, while psychological construction theory claims emotional events as unique, idiosyncratic, and constructed by psychological primitives like core affect and conceptualization, which underlie each emotional event and operate in a predictive framework. Based on the findings of 8 a priori-defined model-specific prediction tests on the neural response amplitudes and patterns, we conclude that the neurobiological basis of affect is primarily characterized by idiosyncratic mechanisms and a common neural basis shared across emotion categories, consistent with psychological construction theory. The findings provide further insight into the organizational principles of the neural basis of affect and brain function in general. Future studies in clinical populations with affective symptoms may reveal the corresponding underlying neural changes from a psychological construction perspective.

The neurobiological reward system and binge eating: A critical systematic review of neuroimaging studies

OBJECTIVE

Changes in reward processing are hypothesized to play a role in the onset and maintenance of binge eating (BE). However, despite an increasing number of studies investigating the neurobiological reward system in individuals who binge eat, no comprehensive systematic review exists on this topic. Therefore, this review has the following objectives: (1) identify structural and functional changes in the brain reward system, either during rest or while performing a task; and (2) formulate directions for future research.

METHODS

A search was conducted of articles published until March 31, 2022. Neuroimaging studies were eligible if they wanted to study the reward system and included a group of individuals who binge eat together with a comparator group. Their results were summarized in a narrative synthesis.

RESULTS

A total of 58 articles were included. At rest, individuals who binge eat displayed a lower striatal dopamine release, a change in the volume of the striatum, frontal cortex, and insula, as well as a lower frontostriatal connectivity. While performing a task, there was a higher activity of the brain reward system when anticipating or receiving food, more model-free reinforcement learning, and more habitual behavior. Most studies only included one patient group, used general reward-related measures, and did not evaluate the impact of comorbidities, illness duration, race, or sex.

DISCUSSION

Confirming previous hypotheses, this review finds structural and functional changes in the neurobiological reward system in BE. Future studies should compare disorders, use measures that are specific to BE, and investigate the impact of confounding factors.

PUBLIC SIGNIFICANCE STATEMENT

This systematic review finds that individuals who binge eat display structural and functional changes in the brain reward system. These changes could be related to a higher sensitivity to food, relying more on previous experiences when making decisions, and more habitual behavior. Future studies should use a task that is specific to binge eating, look across different patient groups, and investigate the impact of comorbidities, illness duration, race, and sex.

Diet or medication in primary care patients with IBS: the DOMINO study - a randomised trial supported by the Belgian Health Care Knowledge Centre (KCE Trials Programme) and the Rome Foundation Research Institute

BACKGROUND

In Europe, IBS is commonly treated with musculotropic spasmolytics (eg, otilonium bromide, OB). In tertiary care, a low fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAP) diet provides significant improvement. Yet, dietary treatment remains to be explored in primary care. We evaluated the effect of a smartphone FODMAP-lowering diet application versus OB on symptoms in primary care IBS.

METHODS

IBS patients, recruited by primary care physicians, were randomised to 8 weeks of OB (40 mg three times a day) or diet and followed for 24 weeks. We compared IBS Symptom Severity Score and the proportion of responders (improvement ≥50 points) in all patients and the subgroup fulfilling Rome IV criteria (Rome+). We also evaluated treatment efficacy, quality of life, anxiety, depression, somatic symptom severity (Patient Health Questionnaire (PHQ15, PHQ9)) and treatment adherence and analysed predictors of response.

RESULTS

459 primary care IBS patients (41±15 years, 76% female, 70% Rome+) were randomised. The responder rate after 8 weeks was significantly higher with diet compared with OB (71% (155/218) vs 61% (133/217), p=0.03) and more pronounced in Rome+ (77% (118/153) vs 62% (98/158), p=0.004). Patients allocated to diet (199/212) were 94% adherent compared with 73% with OB (148/202) (p<0.001). The significantly higher response rate with diet was already observed after 4 weeks (62% (132/213) vs 51% (110/215), p=0.02) and a high symptom response persisted during follow-up. Predictors of response were female gender (OR=2.08, p=0.04) for diet and PHQ15 (OR=1.10, p=0.02) for OB.

CONCLUSION

In primary care IBS patients, a FODMAP-lowering diet application was superior to a spasmolytic agent in improving IBS symptoms. A FODMAP-lowering diet should be considered the first-line treatment for IBS in primary care.

TRIAL REGISTRATION NUMBER

NCT04270487.

Oral Erythritol Reduces Energy Intake during a Subsequent ad libitum Test Meal: A Randomized, Controlled, Crossover Trial in Healthy Humans

The impact of oral erythritol on subsequent energy intake is unknown. The aim was to assess the effect of oral erythritol compared to sucrose, sucralose, or tap water on energy intake during a subsequent ad libitum test meal and to examine the release of cholecystokinin (CCK) in response to these substances. In this randomized, crossover trial, 20 healthy volunteers received 50 g erythritol, 33.5 g sucrose, or 0.0558 g sucralose dissolved in tap water, or tap water as an oral preload in four different sessions. Fifteen minutes later, a test meal was served and energy intake was assessed. At set time points, blood samples were collected to quantify CCK concentrations. The energy intake (ad libitum test meal) was significantly lower after erythritol compared to sucrose, sucralose, or tap water (p < 0.05). Before the start of the ad libitum test meal, erythritol led to a significant increase in CCK compared to sucrose, sucralose, or tap water (p < 0.001). Oral erythritol given alone induced the release of CCK before the start of the ad libitum test meal and reduced subsequent energy intake compared to sucrose, sucralose, or tap water. These properties make erythritol a useful sugar alternative.

Cross-paradigm integration shows a common neural basis for aversive and appetitive conditioning

Sharing imaging data and comparing them across different psychological tasks is becoming increasingly possible as the open science movement advances. Such cross-paradigm integration has the potential to identify commonalities in findings that neighboring areas of study thought to be paradigm-specific. However, even the integration of research from closely related paradigms, such as aversive and appetitive classical conditioning is rare - even though qualitative comparisons already hint at how similar the 'fear network' and 'reward network' may be. We aimed to validate these theories by taking a multivariate approach to assess commonalities across paradigms empirically. Specifically, we quantified the similarity of an aversive conditioning pattern derived from meta-analysis to appetitive conditioning fMRI data. We tested pattern expression in three independent appetitive conditioning studies with 29, 76 and 38 participants each. During fMRI scanning, participants in each cohorts performed an appetitive conditioning task in which a CS+ was repeatedly rewarded with money and a CS- was never rewarded. The aversive pattern was highly similar to appetitive CS+ > CS- contrast maps across samples and variations of the appetitive conditioning paradigms. Moreover, the pattern distinguished the CS+ from the CS- with above-chance accuracy in every sample. These findings provide robust empirical evidence for an underlying neural system common to appetitive and aversive learning. We believe that this approach provides a way to empirically integrate the steadily growing body of fMRI findings across paradigms.

Overnight fasting affects avoidance learning and relief

OBJECTIVES

prolonged fasting influences threat and reward processing, two fundamental systems underpinning adaptive behaviors. In animals, overnight fasting sensitizes the mesolimbic-dopaminergic activity governing avoidance, reward, and fearextinction learning. Despite evidence that overnight fasting may also affect reward and fear learning in humans, effects on human avoidance learning have not been studied yet. Here, we examined the effects of 16 h-overnight fasting on instrumental avoidance and relief from threat omission.

METHODS

to this end, 50 healthy women were randomly assigned to a Fasting (N = 25) or a Re-feeding group (N = 25) and performed an Avoidance-Relief Task.

RESULTS

we found that fasting decreases unnecessary avoidance during signaled safety; this effect was mediated via a reduction in relief pleasantness during signaled absence of threat. A fasting-induced reduction in relief was also found during fear extinction learning.

DISCUSSION

we conclude that fasting optimizes avoidance and safety learning. Future studies should test whether these effects also hold for anxious individuals.

Review article: exclude or expose? The paradox of conceptually opposite treatments for irritable bowel syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is a heterogeneous disorder of gut-brain interaction (DGBI) maintained by interacting biological, psychological, and social processes. Interestingly, there are two contrasting yet evidence-based treatment approaches for reducing IBS symptoms: exclusion diets such as those low in fermentable oligo-, di-, monosaccharides and polyols (FODMAPs) and exposure-based cognitive-behavioural therapy (CBT). Exclusion diets recommend patients avoid foods thought to be symptom-inducing, whereas exposure-based CBT encourages patients to expose themselves to foods.

AIMS

To address the paradox of conceptually opposite exclusion diets and exposure-based CBT for IBS.

METHODS

In this conceptual review, we describe the rationale, practical implementation, evidence base and strengths and weaknesses of each treatment. We conducted up-to-date literature search concerning the low FODMAP diet and CBT, and performed a secondary analysis of a previously conducted trial to illustrate a key point in our review.

RESULTS

The low FODMAP diet has demonstrated efficacy, but problems with adherence, nutritional compromise, and heightened gastrointestinal-specific anxiety raise caution. Exposure-based CBT has demonstrated efficacy with substantial evidence for gastrointestinal-specific anxiety as a key mechanism of action. Mediation analysis also showed that increased FODMAP intake mediated decreased symptom severity in exposure-based CBT. However, there is minimal evidence supporting which treatment "works best for whom" and how these approaches could be best integrated.

CONCLUSIONS

Even though exclusion diets and exposure-based CBT are conceptually opposite, they each have proven efficacy. Clinicians should familiarise themselves with both treatments. Further research is needed on predictors, mechanisms and moderators of treatment outcomes.

Extruded Wheat Bran Consumption Increases Serum Short-Chain Fatty Acids but Does Not Modulate Psychobiological Functions in Healthy Men: A Randomized, Placebo-Controlled Trial

Background

Incorporation of wheat bran (WB) into food products increases intake of dietary fiber, which has been associated with improved mood and cognition and a lower risk for psychiatric disorders such as depression, with short-chain fatty acids (SCFAs) as candidate mediators of these effects. Modifying WB using extrusion cooking increases SCFA production in vitro relative to unmodified WB.

Objective

The aim of this study was to evaluate the effects of extruded WB on psychobiological functioning and the mediating role of SCFAs.

Methods

In a randomized, triple-blind, placebo-controlled trial, 69 healthy male participants consumed 55 g of breakfast cereal containing either extruded WB or placebo daily for 28 days. At pre- and post-intervention visits, the cortisol response to experimentally induced stress was measured as a primary outcome. In addition, serum SCFAs and brain-derived neurotrophic factors were quantified as potential mediators. Secondary psychobiological outcomes included subjective stress responses, responses to experimentally induced fear, cortisol awakening response, heart rate variability, and retrospective subjective mood ratings. Intestinal permeability, fecal SCFAs, and stool consistency were measured as secondary biological outcomes.

Results

Extruded WB increased serum acetate and butyrate (p < 0.05). None of the primary or secondary outcomes were affected by the intervention. Participants who consumed a placebo exhibited an increase in the percentage of fecal dry weight but did not report increased constipation. Despite these statistically significant effects, these changes were small in magnitude.

Conclusions

Extruded WB consumption increased serum short-chain fatty acids but did not modulate psychobiological functions in healthy men. Effective modulation of psychobiological functions may require greater increases in SCFAs than those achieved following extruded WB consumption. Rather than attempting to induce health benefits with a single fiber-rich food, combinations of different fibers, particularly highly fermentable ones, might be needed to further increase SCFA production and uptake in the systemic circulation to observe an effect on psychobiological processes.

Inflammatory Bowel Disease-related Behaviours [IBD-Bx] Questionnaire: Development, Validation and Prospective Associations with Fatigue

BACKGROUND AND AIMS

Disease-related behaviours that may maintain or worsen symptom burden remain largely unexplored in inflammatory bowel disease [IBD]. In this study, we developed and validated an instrument assessing IBD-related, modifiable behaviours and explored which behaviours prospectively correlate with fatigue, a debilitating and common symptom in IBD.

METHODS

Initially, 72 items reflecting IBD-related behaviours were generated based on literature review and input from clinicians and people diagnosed with IBD. During wave 1, 495 IBD patients rated to what extent each behaviour was applicable to them. Additionally, disease activity, fatigue, IBD-related concerns and psychological variables were assessed. During a follow-up visit 4-12 weeks later [wave 2], a random selection of 92 patients from wave 1 completed the measures assessing the IBD-related behaviours, disease activity and fatigue once more.

RESULTS

A principal component analysis with oblique rotation revealed seven components in the 72 IBD behaviours, which could be interpreted as: [1] Avoiding food and activities, [2] Access to toilets, [3] Avoidance of sex, [4] Cognitive avoidance, [5] Not sharing with others, [6] Alternative treatments and [7] Disease management. Each component was reduced to three to five representative items, resulting in a final, 25-item IBD-Bx questionnaire showing good concurrent validity [alphas > 0.63] and reliability. Almost all components were cross-sectionally related to levels of fatigue. Avoiding food and activities and Access to toilets significantly predicted fatigue at wave 2 when controlling for baseline fatigue.

CONCLUSIONS

The IBD-Bx is a valid and reliable questionnaire of IBD-related behaviours, some of which predict future fatigue burden.

When the mind says one thing, but the HPA axis says another: Lack of coherence between subjective and neuroendocrine stress response trajectories in healthy men

Psychological stress triggers the release of cortisol following the activation of the hypothalamic-pituitary-adrenal (HPA) axis and elicits concomitant subjective responses. Coherence among the stress response systems is theoretically expected, presumably to optimize the organism's response to environmental challenges, but has received little empirical support possibly due to the assumption of linear associations. The present study examined the associations between cortisol responses to the Maastricht Acute Stress Test (MAST) and concomitant subjective stress responses as well as mood states over the past weeks in 133 healthy men. Latent class growth analysis (LCGA) was applied on individual cortisol and subjective stress responses to identify homogeneous response trajectories within the larger heterogeneous population and enable testing non-linear relationships while retaining the temporal resolution of the stress responses. LCGA revealed four latent cortisol response classes, labeled as mild responders (n = 15), moderately-low responders (n = 46), moderately-high responders (n = 48), and hyper responders (n = 24). These latent classes were not associated with concomitant subjective stress responses. Similarly, the three distinct latent classes capturing the variability in subjective stress responses were also not associated with concomitant cortisol responses. Experiencing higher levels of stress over the previous weeks, however, increased the likelihood of exhibiting a hyper cortisol stress response profile. Positive and negative affective states, and anxious and depressive symptomology over the previous weeks were not associated with cortisol response trajectories. Contrary to previous findings supporting a quadratic association in healthy females, our results do not support the response coherence hypothesis in healthy males subjected to the MAST, but suggest that recent levels of perceived stress may influence the cortisol response to acute stress.

Effect of slow, deep breathing on visceral pain perception and its underlying psychophysiological mechanisms

BACKGROUND

Studies using somatic pain models have shown the hypoalgesic effects of slow, deep breathing. We evaluated the effect of slow, deep breathing on visceral pain and explored putative mediating mechanisms including autonomic and emotional responses.

METHODS

Fifty-seven healthy volunteers (36 females, mean age = 22.0 years) performed controlled, deep breathing at a slow frequency (6 breaths per minute), controlled breathing at a normal frequency (14 breaths per minute; active control), and uncontrolled breathing (no-treatment control) in randomized order. Moderate painful stimuli were given during each condition by delivering electrical stimulation in the distal esophagus. Participants rated pain intensity after each stimulation. Heart rate variability and self-reported arousal were measured during each condition.

KEY RESULTS

Compared to uncontrolled breathing, pain intensity was lower during slow, deep breathing (Cohen's d = 0.40) and normal controlled breathing (d = 0.47), but not different between slow, deep breathing and normal controlled breathing. Arousal was lower (d = 0.53, 0.55) and heart rate variability was higher (d = 0.70, 0.86) during slow, deep breathing compared to the two control conditions. The effect of slow, deep breathing on pain was not mediated by alterations in heart rate variability or arousal but was moderated by pain catastrophizing.

CONCLUSIONS AND INFERENCES

Slow, deep breathing can reduce visceral pain intensity. However, the effect is not specific to the slow breathing frequency and is not mediated by autonomic or emotional responses, suggesting other underlying mechanisms (notably distraction). Whether a long-term practice of slow, deep breathing can influence (clinical) visceral pain warrants to be investigated.

Gut-brain axis dysfunction underlies FODMAP-induced symptom generation in irritable bowel syndrome

BACKGROUND

FODMAPs produce similar small bowel water and colonic gas in patients with irritable bowel syndrome (IBS) and healthy controls (HCs), despite IBS patients reporting increased gastrointestinal (GI) symptoms.

AIM

To unravel the mechanisms underlying FODMAP-induced symptom reporting, we investigated gut and brain responses to fructan administration in IBS patients and HC.

METHODS

This randomised, double-blind, cross-over study consisted of three visits where fructans (40 g/500 mL saline), glucose (40 g/500 mL saline) or saline (500 mL) were infused intragastrically during 1 h MR brain scanning; abdominal MRI was performed before, 1 h, and 2 h post-infusion. Symptoms were rated using validated scales.

RESULTS

In IBS (n = 13), fructans induced more cramps, pain, flatulence and nausea compared to glucose (P = 0.03, 0.001, 0.009 and <0.001 respectively), contrary to HC (n = 13) (all P > 0.14), with between-group differences for cramps and nausea (P = 0.004 and 0.023). Fructans increased small bowel motility and ascending colonic gas and volume equally in IBS and HC (between-group P > 0.25). The difference in colonic gas between fructans and saline covaried with differences in bloating and cramps in IBS (P = 0.008 and 0.035 respectively). Pain-related brain regions responded differentially to fructans in IBS compared to HC, including the cerebellum, supramarginal gyrus, anterior and midcingulate cortex, insula and thalamus (p_{FWE-corrected}  < 0.05); these brain responses covaried with symptom responses in IBS.

CONCLUSIONS

Fructans increase small bowel motility and colon gas and volume similarly in IBS patients and HC. Increased symptom responses to fructans in IBS covary with altered brain responses in pain-related regions, indicating that gut-brain axis dysregulation may drive FODMAP-induced symptom generation in IBS.

Global prevalence and burden of meal-related abdominal pain

BACKGROUND

Patients with disorders of gut-brain interaction (DGBI) report meal intake to be associated with symptoms. DGBI patients with meal-related symptoms may have more severe symptoms overall and worse health outcomes, but this subgroup has not been well characterized. We aimed to describe the global prevalence of meal-related abdominal pain and characterize this subgroup.

METHODS

The data analyzed originated from the Internet survey component of the population-based Rome Foundation Global Epidemiology Study, completed in 26 countries (n = 54,127). Adult subjects were asked whether they had abdominal pain and how often this was meal-related. Respondents were categorized into "no," "occasional," and "frequent" meal-related abdominal pain groups based on 0%, 10-40%, and ≥50% of the pain episodes being meal-related, respectively. DGBI diagnoses, frequency of other GI symptoms, psychological distress, non-GI somatic symptoms, quality of life, and healthcare utilization were compared between groups. Mixed linear and ordinal regression was used to assess independent associations between psychological distress, non-GI somatic symptoms, quality of life, other GI symptoms, and meal-related abdominal pain.

RESULTS

Overall, 51.9% of the respondents reported abdominal pain in the last 3 months, and 11.0% belonged to the group with frequent meal-related abdominal pain, which included more females and younger subjects. DGBI diagnoses were more common in subjects with frequent meal-related abdominal pain, and the frequency of several GI symptoms was associated with having more frequent meal-related abdominal pain. Having meal-related abdominal pain more frequently was also associated with more severe psychological distress, non-GI somatic symptoms, and a poorer quality of life. The group with frequent meal-related abdominal pain also more often consulted a doctor for bowel problems compared to the other groups of meal-related abdominal pain.

CONCLUSION

Reporting frequent meal-related abdominal pain is common across the globe and associated with other GI and non-GI somatic symptoms, psychological distress, healthcare utilization, and a poorer quality of life. Individuals who frequently experience meal-related abdominal pain also more frequently fulfill the diagnostic criteria for DGBI. Assessing meal-related symptoms in all DGBI patients could be of major importance to improve and individualize symptom management.

The Brain Activation-Based Sexual Image Classifier (BASIC): A Sensitive and Specific fMRI Activity Pattern for Sexual Image Processing

Previous studies suggest there is a complex relationship between sexual and general affective stimulus processing, which varies across individuals and situations. We examined whether sexual and general affective processing can be distinguished at the brain level. In addition, we explored to what degree possible distinctions are generalizable across individuals and different types of sexual stimuli, and whether they are limited to the engagement of lower-level processes, such as the detection of visual features. Data on sexual images, nonsexual positive and negative images, and neutral images from Wehrum et al. (2013) (N = 100) were reanalyzed using multivariate support vector machine models to create the brain activation-based sexual image classifier (BASIC) model. This model was tested for sensitivity, specificity, and generalizability in cross-validation (N = 100) and an independent test cohort (N = 18; Kragel et al. 2019). The BASIC model showed highly accurate performance (94–100%) in classifying sexual versus neutral or nonsexual affective images in both datasets with forced choice tests. Virtual lesions and tests of individual large-scale networks (e.g., visual or attention networks) show that individual networks are neither necessary nor sufficient to classify sexual versus nonsexual stimulus processing. Thus, responses to sexual images are distributed across brain systems.

Better response to low FODMAP diet in disorders of gut-brain interaction patients with pronounced hydrogen response to a nutrient challenge test

BACKGROUND AND AIM

Previous studies have shown a reduction of gastrointestinal symptoms in irritable bowel syndrome (IBS) patients following a low FODMAP diet (LFD). It remains unknown which disorders of gut-brain interaction (DGBI) patients would benefit most from LFD. We aimed to analyze LFD response regarding a preceding nutrient challenge test (NCT).

METHODS

Data of 110 consecutive DGBI patients undergoing NCT and LFD between August 2015 and August 2018 were analyzed retrospectively. LFD response was assessed by changes in IBS Symptom Severity Score (IBS-SSS). In mixed-effects linear regression models, the impact of hydrogen values and abdominal symptoms during NCT, performed with 30-g lactulose and 400-mL liquid test meal, on IBS-SSS changes were analyzed.

RESULTS

Low FODMAP diet induced a significant IBS-SSS reduction of 78 points (95% confidence interval [CI] 50-96; P < 0.001). Patients with higher NCT-induced hydrogen increase during proximal intestinal transit had a significantly better LFD response (-66 IBS-SSS reduction per 10-ppm hydrogen increase, 95% CI -129 to -4, P = 0.045). Additionally, the higher the NCT-induced maximum hydrogen increase during mid-distal and distal intestinal transit, the better are the responses to LFD (-6 IBS-SSS per 10-ppm maximum delta hydrogen, 95% CI -11 to -1, P = 0.040). There was no association of LFD response with abdominal symptom generation during NCT.

CONCLUSIONS

Our study is the first one analyzing and demonstrating significant associations between NCT results and LFD response. These findings are of high clinical importance, as they identify a subgroup of DGBI patients that may profit most from a restrictive LFD as first-line therapy.

Changes in kynurenine pathway metabolites after acute psychosocial stress in healthy males: a single-arm pilot study

Chronic stress is associated with an increased conversion of tryptophan (TRP) into kynurenine (KYN). However, only a few studies investigated KYN pathway metabolite concentrations following acute stress in healthy subjects. We hypothesized that TRP/KYN metabolism changes following acute stress, and that KYN pathway metabolites are associated with cortisol and subjective stress responses. In a single-arm pilot study, we explored whether KYN pathway metabolites concentrations were altered after acute stress induced by the Maastricht Acute Stress Test in healthy males (n = 56, mean age: 27 (SD = 4.5) years, BMI: 23 (SD = 1.8) kg/m²). In particular, we examined whether concentrations of TRP decreased, and KYN, kynurenic acid (KYNA), and the ratio of KYN to TRP (KYN:TRP) increased after acute stress. Furthermore, we assessed whether cortisol and subjective stress responses correlated with KYN pathway metabolite measures after stress induction, based on both the area under the curve with respect to the ground (AUCg) as well as the incremental area under the curve (AUCi). Concentrations of TRP, KYN, KYNA, and KYN:TRP were significantly lower after stress induction compared to pre-stress induction (all p < 0.01). AUCi and AUCg reflecting cortisol and subjective stress responses did not correlate with AUCi and AUCg reflecting KYN pathway metabolite responses. These preliminary results indicate that KYN pathway metabolites are lower after acute psychosocial stress induction. Moreover, although chronic stress and subsequent prolonged elevated cortisol concentrations and subjective stress stimulate the conversion of TRP into KYN, acute stress is not associated with such conversion up to 35 minutes after stress induction.

Erythritol and xylitol differentially impact brain networks involved in appetite regulation in healthy volunteers

BACKGROUND

There is a growing consensus that sugar consumption should be reduced and the naturally occurring, low-calorie sweeteners xylitol and erythritol are gaining popularity as substitutes, but their effect on brain circuitry regulating appetite is unknown.

AIM

The study's objective was to examine the effects of the two sweeteners on cerebral blood flow (rCBF) and resting functional connectivity in brain networks involved in appetite regulation, and test whether these effects are related to gut hormone release.

METHODS

The study was performed as a randomized, double-blind, placebo-controlled, cross-over trial. Twenty volunteers received intragastric (ig) loads of 50g xylitol, 75g erythritol, 75g glucose dissolved in 300mL tap water or 300mL tap water. Resting perfusion and blood oxygenation level-dependent data were acquired to assess rCBF and functional connectivity. Blood samples were collected for determination of CCK, PYY, insulin and glucose.

RESULTS

We found: (i) xylitol, but not erythritol, increased rCBF in the hypothalamus, whereas glucose had the opposite effect; (ii) graph analysis of resting functional connectivity revealed a complex pattern of similarities and differences in brain network properties following xylitol, erythritol, and glucose; (iii) erythritol and xylitol induced a rise in CCK and PYY, (iv) erythritol had no and xylitol only minimal effects on glucose and insulin.

CONCLUSION

Xylitol and erythritol have a unique combination of properties: no calories, virtually no effect on glucose and insulin while promoting the release of gut hormones, and impacting appetite-regulating neurocircuitry consisting of both similarities and differences with glucose.

Controlled breathing and pain: Respiratory rate and inspiratory loading modulate cardiovascular autonomic responses, but not pain

Slow, deep breathing (SDB) is a common pain self-management technique. Stimulation of the arterial baroreceptors and vagal modulation are suggested, among others, as potential mechanisms underlying the hypoalgesic effects of SDB. We tested whether adding an inspiratory load to SDB, which results in a stronger baroreceptor stimulation and vagal modulation, enhances its hypoalgesic effects. Healthy volunteers performed SDB (controlled at 0.1 Hz) with and without an inspiratory threshold load. Controlled breathing (CB) at a normal frequency (0.23 Hz) was used as an active control. Each condition lasted 90 s, included an electrical pain stimulation on the hand, and was repeated four times in a randomized order. Pain intensity, self-reported emotional responses (arousal, valence, dominance), and cardiovascular parameters (including vagally-mediated heart rate variability) were measured per trial. A cover story was used to limit the potential effect of outcome expectancy. Pain intensity was slightly lower during SDB with load compared with normal-frequency CB, but the effect was negligible (Cohens d < 0.2), and there was no other difference in pain intensity between the conditions. Heart rate variability was higher during SDB with/without load compared with normal-frequency CB. Using load during SDB was associated with higher heart rate variability, but less favorable emotional responses. These findings do not support the role of baroreceptor stimulation or vagal modulation in the hypoalgesic effects of SDB. Other mechanisms, such as attentional modulation, warrant further investigation.

A randomized double-blind placebo-controlled crossover pilot study: Acute effects of the enzyme α-galactosidase on gastrointestinal symptoms in irritable bowel syndrome patients

BACKGROUND

Postprandial symptoms presumably related to intestinal gas production are common in patients with irritable bowel syndrome (IBS). The aim of the study was to assess if oral α-galactosidase is superior to placebo in reducing gastrointestinal (GI) symptoms and intestinal gas production after ingestion of carbohydrate-rich meals in adult patients with IBS.

METHODS

We studied the effect of 1200 GaIU/meal α-galactosidase (Nogasin^® ) or placebo capsules on GI symptoms in patients with IBS after three standardized, meals high in oligosaccharides, in a randomized, double-blind, crossover study. The intensity of eight GI symptoms was rated, and breath hydrogen and methane were measured every 30 min during 7.5 h. The severity of GI symptoms the following morning was assessed and compared with baseline.

S KEY RESULTS

Twenty adult patients with IBS (19 females), mean age 49 years (range 22-75 years), were included. All test meals were well tolerated but induced a gradual increase in GI symptom severity. Neither GI symptom ratings over time, nor hydrogen and methane concentrations differed between the days with α-galactosidase or placebo. The severity of abdominal pain and bloating was lower the following morning, but with no differences between α-galactosidase and placebo.

CONCLUSIONS & INFERENCES

The use of α-galactosidase together with meals high in oligosaccharides was in this pilot study not superior to placebo in reducing postprandial GI symptoms or the concentration of hydrogen and methane in expired air in IBS.

The endocrine effects of bitter tastant administration in the gastrointestinal system: intragastric versus intraduodenal administration

Bitter tastants are recently introduced as potential hunger-suppressive compounds, the so-called "Bitter pill." However, the literature about bitter administration lacks consistency in methods and findings. We want to test whether hunger ratings and hormone plasma levels are affected by: 1) the site of administration: intragastrically (IG) or intraduodenally (ID), 2) the bitter tastant itself, quinine hydrochloride (QHCl) or denatonium benzoate (DB), and 3) the timing of infusion. Therefore, 14 healthy, female volunteers participated in a randomized, placebo-controlled six-visit crossover study. After an overnight fast, DB (1 µmol/kg), QHCl (10 µmol/kg), or placebo were given IG or ID via a nasogastric feeding tube. Blood samples were taken 10 min before administration and every 10 min after administration for a period of 2 h. Hunger was rated at the same time points on a visual analogue scale. ID bitter administration did not affect hunger sensations, motilin, or acyl-ghrelin release compared with its placebo infusion. IG QHCl infusion tended to suppress hunger increase, especially between 50 and 70 min after infusion, simultaneously with reduced motilin values. Here, acyl-ghrelin was not affected. IG DB did not affect hunger or motilin, however acyl-ghrelin levels were reduced 50-70 minutes after infusion. Plasma values of glucagon-like peptide 1 and cholecystokinin were too low to be properly detected or to have any physiological relevance. In conclusion, bitter tastants should be infused into the stomach to reduce hunger sensations and orexigenic gut peptides. QHCl has the best potential to reduce hunger sensations, and it should be infused 60 min before food intake.NEW & NOTEWORTHY Bitter tastants are a potential new weight-loss treatment. This is a noninvasive, easy approach, which should be received with considerable enthusiasm by the public. However, literature about bitter administration lacks consistency in methods and findings. We summarize how the compound should be given based on: the site of administration, the best bitter compound to use, and at what timing in respect to the meal. This paper is therefore a fundamental step to continue research toward the further development of the "bitter pill."

Vasovagal reactions following venepuncture result in aberrant stress-induced cortisol levels

Venepuncture is recognized as a potent stressor and, by activating the hypothalamic-pituitary-adrenal (HPA) axis, can interfere with measuring subsequent HPA axis indices such as cortisol. A resting period of 110 min is recommended between venepuncture and the commencement of psychosocial stress induction or cortisol measurement to allow cortisol levels to return to baseline first. In experiment 1 (n = 65), in which stress induction occurred 120 min after venepuncture, we observed three cortisol stress response patterns: conventional response ("responders", 77%), conventional non-response ("non-responders", 6.15%), and aberrant non-response characterized by high baseline (pre-stress) cortisol levels ("high-baseliners", 16.9%). Based on subjective clinical observation, the aberrant non-response was exclusively present in those who experienced vasovagal reactions during venepuncture, ranging from nervousness, lightheadedness, nausea, feeling of being extremely hot or cold, confusion, slight inability to speak, weakness and visual disturbances, to loss of consciousness (syncope). In experiment 2 (n = 79), we showed that allowing 210 min between venepuncture and stress induction permits the return of cortisol levels back to baseline even in participants who experience vasovagal reactions, thereby allowing for the exhibition of a conventional cortisol stress response. In sum, while 110 min may be sufficient to circumvent the usual effects of venepuncture on cortisol levels, 210 min are needed to effectively adjust for the effects of venepuncture-induced vasovagal reactions and the subsequent sustained rise in cortisol. Allowing sufficient time between venepuncture and stress induction or cortisol measurement should also prevent misclassification of participants who show aberrant responses as non-responders or anticipatory responders.

Proton Pump Inhibitors Reduce Duodenal Eosinophilia, Mast Cells, and Permeability in Patients With Functional Dyspepsia

BACKGROUND & AIMS

Despite the growing recognition of duodenal alterations in the pathophysiology of functional dyspepsia (FD), the effect and mechanism of proton pump inhibitors (PPIs) or first-line therapy remain unclear. We studied duodenal and systemic alterations in relation to PPI therapy in patients with FD and healthy volunteers (HVs).

METHODS

We performed a prospective interventional study assessing symptoms (Patient Assessment of Gastrointestinal Symptom Severity Index), duodenal alterations, and systemic factors in patients with FD ("FD-starters") and HVs before and after PPI therapy (pantoprazole 40 mg once daily for 4 weeks). Duodenal mucosal eosinophils, mast cells and permeability were quantified. Luminal pH and bile salts were determined in duodenal aspirates. Procedures were also performed in PPI-refractory patients with FD ("FD-stoppers") before and 8 weeks after PPI withdrawal. Between- and within-group changes from baseline and associations with duodenal or systemic factors were analyzed using linear mixed models.

RESULTS

The study was completed by 30 HV, 27 FD-starters, and 18 FD-stoppers. Symptoms and duodenal eosinophils, mast cells (all, P < .0001), and paracellular passage (P = .02) were significantly higher in FD-starters vs HVs and reduced with PPI therapy. Symptoms and duodenal immune cells also decreased in FD-stoppers off PPIs. In contrast, immune cells and permeability increased in HVs on PPIs. Dyspeptic symptoms correlated with eosinophils before and during PPI therapy, and increased eosinophils and permeability in HVs on PPIs were associated with changes in bile salts.

CONCLUSIONS

We provide the first prospective evidence for eosinophil-reducing effects as a therapeutic mechanism of PPIs in FD, with differential effects in HVs pointing to a role of luminal changes. ClinicalTrials.gov, Number: NCT03545243.

Association between pain sensitivity and gray matter properties in the sensorimotor network in women with irritable bowel syndrome

BACKGROUND

Enhanced perception of visceral stimuli is an important feature of Irritable Bowel Syndrome (IBS), but it is not known whether visceral sensitivity is associated with regional structural brain properties in IBS.

METHODS

Structural brain magnetic resonance imaging data from 216 women with IBS and 138 healthy women were parcellated with FreeSurfer to define regional gray matter morphometry (volume, cortical thickness, surface area and mean curvature) in the sensorimotor network. General linear models were used to detect group differences between IBS and health. In a second set of 48 female IBS patients, pain threshold, pain intensity ratings during rectal balloon distension, and reported levels of abdominal pain and bloating were correlated with brain regions that showed differences between IBS and health in the first data set.

KEY RESULTS

Several statistically significant differences between IBS patients and healthy controls were found, mainly higher gray matter volume and cortical thickness in primary somatosensory cortex, secondary somatosensory cortex, and subcortical regions, and lesser gray matter volume, surface area and cortical thickness in posterior insula and superior frontal gyrus. Pain intensity ratings during rectal distension were associated with left primary somatosensory cortical thickness, and pain threshold was associated with right nucleus accumbens volume.

CONCLUSIONS AND INFERENCES

Regional gray matter differences in sensorimotor network are associated with visceral sensitivity and may represent neuroplastic changes in female IBS patients.

The respiratory occlusion discrimination task: A new paradigm to measure respiratory interoceptive accuracy

Interoception, or the sense of the internal state of the body, is hypothesized to be essential for a wide range of psychobiological processes and the development and perpetuation of several (mental) health problems. However, the study of interoceptive accuracy, the objectively measured capacity to detect or discriminate conscious bodily signals, has been hampered by the use of tasks with questionable construct validity and is often limited to studying interoception solely in the cardiac domain. We developed a novel task to measure interoceptive accuracy in the respiratory domain, the respiratory occlusion discrimination (ROD) task. In this task, interoceptive accuracy is defined as an individual's ability to detect small differences in lengths of short respiratory occlusions, assessed by means of an adaptive staircase procedure. This article describes a validation study (N = 97) aimed at investigating the internal consistency, test-retest reliability, and discriminant validity of the ROD task. The average just noticeable difference of lengths of respiratory occlusion was 74.22 ms, with large inter-individual variability (SD = 37.1 ms). The results of the validation study indicate acceptable internal consistency (Cronbach's alpha = 0.70), 1-week test-retest reliability (r = 0.53), and discriminant validity, as indicated by a lack of correlation between the ROD task and an auditory discrimination task with identical design (r = 0.18), and a weak correlation with breathing behavior (r = -0.27). The ROD task is a promising novel paradigm to study interoceptive accuracy and its role in various psychobiological processes and disorders.

Imaging Brain Mechanisms of Functional Somatic Syndromes: Potential as a Biomarker?

When patients present with persistent bodily complaints that cannot be explained by a symptom-linked organic pathology (medically unexplained symptoms), they are diagnosed with 'functional' somatic syndromes (FSS). Despite their prevalence, the management of FSS is notoriously challenging in clinical practice. This may be because FSS are heterogeneous disorders in terms of etiopathogenesis. They include patients with primarily peripheral dysfunction, primarily centrally driven somatic symptoms, and a mix of both. Brain-imaging studies, particularly data-driven pattern recognition methods using machine learning algorithms, could provide brain-based biomarkers for these clinical conditions. In this review, we provide an overview of our brain imaging data on brain-body interactions in one of the most well-known FSS, irritable bowel syndrome (IBS), and discuss the possible development of a brain-based biomarker for FSS. Anticipation of unpredictable pain, which commonly elicits fear in FSS patients, induced increased activity in brain areas associated with hypervigilance during rectal distention and non-distention conditions in IBS. This was coupled with dysfunctional inhibitory influence of the medial prefrontal cortex (mPFC) and pregenual anterior cingulate cortex (pACC) on stress regulation systems, resulting in the activated autonomic nervous system (ANS) and neuroendocrine system stimulated by corticotropin-releasing hormone (CRH). IBS subjects with higher alexithymia, a risk factor for FSS, showed stronger activity in the insula during rectal distention but reduced subjective sensitivity. Reduced top-down regulation of the ANS and CRH system by mPFC and pACC, discordance between the insula response to stimulation and subjective sensation of pain, and stronger threat responses in hypervigilance-related areas may be a candidate brain-based biomarker.

Colon-delivered short-chain fatty acids attenuate the cortisol response to psychosocial stress in healthy men: a randomized, placebo-controlled trial

Short-chain fatty acids (SCFAs) are products of microbial fermentation of dietary fiber in the colon and may mediate microbiota-gut-brain communication. However, their role in modulating psychobiological processes that underlie the development of stress- and anxiety-related disorders is not mechanistically studied in humans. In this triple-blind, randomized, placebo-controlled intervention trial, we examine in a parallel group design the effects of 1-week colonic SCFA-mixture delivery in doses equivalent to fermentation of 10 g or 20 g of arabinoxylan oligosaccharides on responses to psychosocial stress and fear tasks in 66 healthy men. We demonstrate that low and high doses of SCFAs significantly attenuate the cortisol response to psychosocial stress compared to placebo. Both doses of SCFAs increase serum SCFA levels and this increase in circulating SCFAs co-varies significantly with the attenuation of the cortisol response to psychosocial stress. Colonic SCFA delivery does not modulate fecal SCFA concentrations, serum brain-derived neurotrophic factor, cortisol awakening response, fear learning and extinction, or subjective mood ratings. These results demonstrate that colon-delivered SCFAs modulate hypothalamic-pituitary-adrenal axis reactivity to psychosocial stress, thereby supporting their hypothesized role in microbiota-gut-brain communication.