BACKGROUND:Perianal Crohn's disease (pCD) is a severe pediatric phenotype with high morbidity. Although antitumor necrosis factor (TNF) agents are first-line therapy, remission is not achieved in a subset of patients. We aimed to evaluate clinical and radiological outcomes of ustekinumab (UST) in pediatric patients with pCD. METHODS:This is a multicenter retrospective study including pediatric patients with pCD treated with UST between 2016 and 2023. Primary outcomes were clinical and radiological remission at predefined time points. Clinical remission was defined as absence of fistula drainage without antibiotics or unplanned perianal interventions. Radiological remission was defined as a Pediatric MRI-Based perianal Crohn's Disease (PEMPAC) score of <10 on pelvic MRI. RESULTS:Fifty patients were included, of whom 2 were anti-TNF-naive. The median age at UST initiation was 15 years (IQR 12.4-16.2). Clinical remission was observed in 46% (23/50; P = .006 vs baseline), 48% (23/48; P = .036 vs baseline), and 42% (19/45; P = .13 vs baseline) at weeks 26, 52, and 104, respectively. Radiological remission was 29% (10/34) and 30% (13/43) at weeks 52 and 104, respectively (both P < .01 vs baseline). In multivariable analysis, higher baseline PEMPAC scores were independently associated with lower odds of both clinical (P < .01; OR 0.88, 95% CI 0.68-0.95) and radiological remission (P < .01; OR 0.81, 95% CI 0.62-0.94). CONCLUSIONS:UST was associated with perianal clinical remission in a substantial proportion of pediatric patients, approaching 50% at 1 year, and radiological healing in about one-third at 2 years, supporting its potential role in pediatric pCD.

Abstract Background Sigmoidoscopy is a less invasive procedure than full colonoscopy, demands simpler preparation, requires shorter procedure time, and may be conducted with lighter sedation. Despite these advantages and the continuous nature of inflammation in ulcerative colitis (UC), which typically decreases from distal to proximal colon, the FDA recently requests full colonoscopy to assess UC in clinical trials (i.e. 3 colonoscopies in 54 weeks). Data to support this requirement are scarce in children. We, thus, aimed to assess the necessity of full colonoscopy versus limited sigmoidoscopy in pediatric UC. Methods We included two prospectively enrolled cohorts of children (0-18 years) with UC, both with identical data collection relevant to this study: one from a single-center prospective registry, and the other from a prospective validation of the TUMMY-UC, a patient-reported signs and symptoms for pediatric UC. In addition to explicit clinical, disease activity, labs and demographic data, the Ulcerative Colitis Endoscopic Index of Severity (UCEIS) was recorded prospectively for each colonic segment. The first colonoscopy available after the time of diagnosis was included to better mirror the scenario of post-treatment follow-up monitoring, since the diagnostic procedure should always be full colonoscopy. Results A total of 85 patients were included (mean age 14 ± 3.4, 11 [13%] with endoscopic healing, 45 [53%] with mild colitis and 29 [34%] with moderate-severe colitis). The median UCEIS scores decreased progressively from the rectum and sigmoid (2, IQR:0-4) to the more proximal colon (descending 1, IQR:0-3; transverse and ascending 0, IQR:0-2; p < 0.001). Only 3 patients (3.5%) had inflammation in proximal segments without having inflammation in the rectosigmoid region. Another 10 patients (12%) had higher inflammation scores in the proximal colon than in the rectosigmoid (i.e. reverse gradient), though inflammation was still present in the rectosigmoid region. Conclusion In 96.5% of cases, endoscopic healing in the rectosigmoid region reflected endoscopic healing in the entire colon in children with UC. When inflammation was present in the rectosigmoid, in 86% the degree of colitis reflected the maximal endoscopic severity of the entire colon. These findings suggest that sigmoidoscopy may be a suitable routine post-treatment surveillance tool for pediatric UC patients and in the research setting in order to maximize feasibility and ethical considerations of clinical trials.

Abstract Background Tasty&HealthyTM (T&H) is a whole food diet aimed at alleviating inflammation in Crohn’s disease (CD). It excludes processed food, gluten, red meat, and dairy (except for plain yogurt), but does not include mandatory ingredients or partial enteral nutrition with formula as does the CD Exclusion Diet. In this RCT we evaluated T&H diet as an intervention for persistent subclinical inflammation compared with continuing habitual diet. (NCT#04239248; TASTI-E). Methods Patients with CD, aged 6-40 years, in clinical remission or with minimal symptoms (wPCDAI<20/CDAI<200), were randomized if their MINI-index was ≥8 (i.e. bowel inflammation), to receiving either T&H or continuing their habitual diet for 8 weeks. Patients in the latter group were also offered T&H after completing the initial 8 week randomization period. The primary outcome was calprotectin-defined response (i.e. reduction of >50%). Secondary outcomes included adherence, MINI-index, and CRP. Due to COVID-19-related slow enrolment, the study was terminated early, and thus analyses are exploratory on a per-protocol basis. Results 46 patients were randomized (mean age 18.2±7.6 years; median disease duration 9.01 months, IQR 2.9-17.1); 19 were assigned to T&H and 27 to the habitual group. The primary endpoint was achieved, with 7 patients (37%) in the T&H group achieving calprotectin response, vs 4 (15%) in the habitual group (RR 3.23 [95% CI 1.15-9.01]; p=0.028). A pre-post comparison of 15 patients who completed 8 weeks of habitual diet and crossed-over to T&H, showed higher rates of calprotectin<250 mcg/g at week 16 compared with their baseline at week 8 (47% vs. 17%, p=0.005) and MINI<8 (60% vs 20%, p=0.0013). Additionally, compared with the habitual diet, the improvement in CRP 0.48 (0.18-0.81) vs. 0.36 (0.1-0.36); p=0.0012) and MINI (10 (9-13) vs. 7 (5-10.5); p=0.047) was higher in the T&H arm, respectively. The absence of gluten levels in stool was used as a measure of adherence to the T&H diet. At week 8, only 2/13 patients (15%) in the T&H group tested positive for stool gluten, compared to 18/20 patients (90%) in the habitual diet group (p=0.002), demonstrating high adherence to T&H. Patients in the T&H arm met over 95% of Dietary Reference Intakes (DRI) for key macro- and micronutrients. No significant differences were found between the groups except for higher potassium and fiber in the T&H group (p=0.018 and p<0.001, respectively). Conclusion The T&H diet is effective in reducing inflammation in children and adults with CD who have subclinical inflammation. The flexibility of T&H without the need for formula feeds or mandatory ingredients is associated with high adherence.

BACKGROUND AND AIMS:The pathophysiology of pediatric inflammatory bowel disease (PIBD), encompassing Crohn's disease (CD) and ulcerative colitis (UC), is not entirely understood. Dysregulation of the intestinal microbiome is recognized as both a disease-driving and a potential therapeutic target. This study aimed to systematically analyze gut microbiome compositions and its applicability as a biomarker for disease progress and treatment response. METHODS:Bibliographic and nucleotide databases were searched. Raw 16S-rRNA sequencing reads were subjected to a uniform downstream dada2/phyloseq pipeline to extract taxonomy, community structure, and abundance information. Patient metadata were extracted from publications, and study authors were contacted for further details if required. RESULTS:Twenty-six studies comprising 3956 stool samples (CD 41%, UC 36%, 23% healthy) were included in the analyses. Median age of individuals was 12 (interquartile range 4). Sex distribution was comparable. Alpha diversity was reduced between the healthy and both UC and CD treatment-naïve groups (P < .001) and further reduced with increasing clinical disease activity. Beta diversity revealed altered community structure in treatment-naïve children with PIBD (P < .001). This alteration remained in patients in clinical remission (P < .001). Machine learning models discriminated between treatment-naïve patients with CD or UC with an area under the receiver operating characteristics curve (AUROC) of 98%. Microbial communities differed between patient responders versus nonresponders to treatment (P < .001). Further, microbial community profiling distinguished treatment response (eg, steroid, nutrition, or TNFα) with AUROCs of 82%-90%. CONCLUSIONS:Gut microbial community structure is substantially altered in active and inactive PIBD and may be utilized as a biomarker for differentiating PIBD subtype and predicting treatment response.

Abstract Background Crohn’s disease (CD) prevalence is rising globally, but its pathogenesis remains unclear. Our group found specific microbes predict future CD risk in healthy first-degree relatives (FDR), whereas high fecal calprotectin (FCP) level (>100ug/g) was also significantly associated with a 6-fold higher risk of CD onset. However, the influence of FCP on how microbial communities contribute to CD risk remains unknown. Understanding microbial interactions with gut inflammation may offer insights into CD onset. Aims This study investigates how microbial composition and function contribute to CD risk in healthy in association with their baseline FCP levels. Methods Healthy FDRs from the CCC-GEM Project were followed for CD onset. Using baseline stool samples, microbial compositions were analyzed with 16S rRNA sequencing and functional predictions with PICRUSt2. Cox PH models assessed relationships between microbiome composition, functional pathways, and CD risk stratified by high or low levels of subclinical inflammation, defined by FCP with a cut-off of 100 ug/g (FCP>100 and FCP<100, respectively). q<0.1 was considered statistically significant. Results We followed 3430 FDRs for a median of 7.7 years, among which 76 developed CD. In the subgroup with FCP>100 a higher abundance of Ruminococcus torques group, an undefined Ruminococcus genus, and Romboutsia were significantly associated with an increased risk of CD. In contrast, Oscillospiraceae family was consistently associated with a lower CD risk in both FCP>100 and FCP<100 subgroups. Microbial functional pathways analysis revealed that peptidoglycan-N-acetylmuramic acid deacetylase, 4’-phosphopantetheinyl transferase, and iron(III) transport system ATP-binding protein were consistently associated with a decreased risk of CD in both FCP>100 and FCP<100 subgroups. However, pathways including Flagellar motor switch protein FliN and Carboxynorspermidine decarboxylase were associated with increased risk of CD, but only in the FCP>100 subgroup. In contrast, geranylgeranyl diphosphate synthase and heat shock protein HspR were associated with increased CD risk in the FCP<100 subgroup. Conclusions The microbial contribution to CD risk in healthy FDRs may vary depending on baseline FCP levels. Specific taxa and functional pathways were identified as contributors to CD risk in FDRs in the presence or absence of intestinal inflammation. Notably, the Oscillospiraceae family was consistently associated with a decreased risk of CD, highlighting its potential as a therapeutic target in the pre-clinical phase of CD. Funding Agencies None

Abstract Background Primary sclerosing cholangitis (PSC) is a rare cholestatic liver disease that frequently coexists with inflammatory bowel disease (IBD). Data comparing the paediatric- and adult-onset PSC-IBD are lacking. We compared disease characteristics and the clinical course of PSC-IBD between Canadian children and adults. Methods This was a multi-center retrospective cohort study including eight paediatric centers from different provinces across Canada including (Ontario, Alberta, Nova Scotia, Manitoba) and four adult centers from the province of Ontario, including patients diagnosed with PSC-IBD from 1985-2023. Patient and disease characteristics and outcome data were extracted from the clinical charts. We compared patient demographics, disease course, laboratory and imaging results, and complications including liver transplant among paediatric- and adult-onset PSC-IBD. Continuous data were reported as median (Q1-Q3) and compared with the Wilcoxon Rank Sum test, and categorical data were reported as number (%) and compared with chi-square or Fisher exact tests. We compared the time to transplant with the log-rank test. Results We included 521 patients (228 children, median follow-up 3.3 (Q1-Q3 1.5-5.8) years; 293 adults, median follow-up 9.8 (Q1-Q3 4.3-16.0) years (Table-1). The interval between PSC and IBD diagnosis was longer in adults. Small duct disease and PSC with autoimmune hepatitis (AIH) features were more common in children, with corresponding higher ALT and more frequently positive autoantibodies. Rates of portal hypertension at PSC diagnosis were similar in both groups. Ulcerative colitis predominated in both groups with more IBD-unclassified in children. Colitis was most severe in the right colon in a third of children and adults. Children were more often treated with ursodeoxycholic acid, vancomycin, corticosteroids and immunomodulators. Adult patients experienced a higher proportion of adverse liver events over the entire follow-up duration, but time to event analysis showed similar rates of progression to liver transplant (log-rank p=0.075; 2- and 5-year survival with native liver in paediatric vs. adult: 97% and 90% vs. 94% and 84%). (Figure-1) Conclusion In this large Canadian multi-center cohort of PSC-IBD, paediatric-onset disease was characterized by more frequent small duct disease and features of AIH. The interval between IBD and PSC diagnosis was far longer in adults. Although a greater proportion of adult-onset patients experienced adverse liver outcomes overall, rates of transplant at 2 and 5 years were similar between groups, suggesting that PSC progression may in fact be similar.

Abstract Background Antimicrobial serologies have been associated with Inflammatory Bowel Disease (IBD) type and Crohn’s disease (CD) progression. However, prospective pediatric data examining these associations while considering disease location are sparse. Aims 1) Describe rates of serology positivity by disease location; 2) Assess the ability of serologies to predict CD progression to stricturing (B2) /penetrating (B3) behaviour, while accounting for IBD location. Methods Children with CD enrolled in the prospective multicentre Canadian Children IBD Network (CIDsCaNN) were included. ASCA IgA and IgG, CBir1, OmpC and ANCA positivity were measured centrally at Cedars-Sinai. We assessed variables at diagnosis and last follow up. We used Pearson’s Chi-Squared test to compare proportions and Mann-Whitney U test to compare medians between groups. We used multivariable Cox regression to determine the association between serologies and progression to B2/B3 amongst CD patients with B1 at diagnosis, while accounting for L1 location. We calculated area under the ROC curve (AUC) to quantify predictive ability. Results There were 512 CD patients included: median age 13 y (IQR 10.8-14.9), follow up 3.3 y (IQR 1.9-5.0). There were 50/452 (11%) B1 CD patients who progressed (L1: 16/77 (21%); L2: 7/112 (6%); L3: 27/241 (11%)). ASCA+ was more frequent among patients with L1/L3 compared to L2 CD (28% vs 13%, p=0.009), while CBir1+ and OmpC+ rates did not differ by CD location (55% vs 48%, p=0.19 and 9% vs 9%, p=0.85). ANCA+ rate was higher among L2 CD compared to L1/L3 CD (30% vs 10%, p<0.001). In univariate survival analysis, CBir1+, ASCA+ and L1 were associated with progression to B2/B3 (Table 1). In multivariable analysis, only positivity for CBir1+ and L1 were associated with progression. CBir1 titre had only moderate ability to predict progression (AUC 0.65 (95%CI 0.57-0.72)). Conclusions While ASCA and CBir1 are associated with complicated CD in univariate analysis, this appears to be mediated by small bowel location for ASCA. While CBir1 was independently associated with B2/B3 disease, its predictive ability alone was limited. Table 1. Unadjusted and Adjusted Hazard Ratios for Progression to B2 or B3 Complications Funding Agencies CIHRCh.I.L.D Foundation

BACKGROUND & AIMS:Tasty&Healthy (T&H) is a whole food diet for Crohn's disease (CD) that excludes processed food, gluten, red meat, and dairy, without requiring formula or mandatory ingredients. TASTI-MM was a clinician-blinded, randomized controlled trial comparing tolerability and effectiveness of T&H vs exclusive enteral nutrition (EEN). METHODS:Patients with biologic-naïve mild to moderate CD and aged 6-25 years were randomized to either T&H or EEN for 8 weeks, receiving weekly dietary support. Tolerability was evaluated by weekly interviews, questionnaires, and intake diaries. Other outcomes included symptomatic remission, Mucosal-Inflammation Noninvasive index, calprotectin, C-reactive protein, and erythrocyte sedimentation rate. Fecal microbiome was analyzed by metagenomics at baseline, week 4, and week 8. Data were analyzed by the intention-to-treat approach unless specified otherwise. RESULTS:Among 83 included patients (n = 41 T&H, n = 42 EEN; mean ± SD age, 14.5 ± 3.7 years), 88% tolerated T&H vs 52% for EEN (adjusted odds ratio [aOR], 7.7; 95% CI, 2.4-25; P < .001). Calprotectin, C-reactive protein, and erythrocyte sedimentation rate decreased significantly in both groups, with no between-group differences. Symptomatic remission was achieved in 56% of the T&H group vs 38% of the EEN group (aOR, 2.5; 95% CI, 0.98-6.3; P = .1; per-protocol: 67% vs 76%; P = .47). Calprotectin <250 μg/g was achieved in 34% vs 33% (aOR, 0.97; 95% CI, 0.37-2.6; P = .84) and Mucosal-Inflammation Noninvasive index score <8 in 44% vs 31% (aOR, 1.8; 95% CI, 0.7-4.5; P = .33). Microbiome α-diversity improved in the T&H arm and declined in the EEN arm, showing superior species richness at both week 4 and week 8. Species associated with bowel inflammation, such as Ruminococcus gnavus, decreased in T&H and increased in EEN (q < .001). CONCLUSIONS:T&H demonstrated better tolerability than EEN for inducing remission in mild to moderate CD, while positively affecting the microbiome. CLINICALTRIALS:gov, Number: NCT04239248.

Abstract Background The Tasty&Healthy™ (T&H) diet offers a flexible alternative to exclusive enteral nutrition (EEN) for inducing remission in Crohn’s disease (CD). Unlike CDED, it excludes processed foods, gluten, red meat, and most dairy but does not rely on formula or mandatory ingredients. The "MyTasty" trial aimed to assess the effectiveness and feasibility of T&H for maintaining remission in children and adults with CD, with gradual reintroduction of gluten and dairy Methods Patients with CD (4-37 years of age) who entered deep remission (i.e. MINI index <8 and wPCDAI<12.5/CDAI<150) with dietary treatment during one of the two induction RCTs of T&H (TASTI-MM and TASTI-E), were enrolled in this 16-week, open-label maintenance trial. Participants followed T&H with gradual reintroduction of gluten, milk, and other dairy products monthly, dictated by home-based fecal calprotectin (FC). FC increase by >30% suggested failure of the new food and thus it was excluded again. Results Altogether, 43 patients (mean age 16±5.8 years, 10 adults, median disease duration 1.5 months [IQR 0.49–2.95]) were enrolled, with 34 (79%) completing the 16-week dietary period. At week 16, 32/43 (75%) had FC<250, 32/43 (75%) had normal CRP, 34/43 (79%) had MINI-index<8 (implying mucosal healing), 37/43 (86%) were in clinical remission (wPCDAI <12.5/CDAI <150), and 21/43 (49%) achieved deep remission (clinical remission, normal CRP, and FC<250, figure 1). Of the 34 completing the study, 19 (55%) successfully introduced gluten, milk, and dairy without increases in inflammation markers, and 2 introduced all three but with an FC increase at week 16. Among others, 6 tolerated milk/dairy but not gluten, 1 tolerated only milk, 3 tolerated gluten but not milk/dairy, and 2 tolerated gluten and milk but not other dairy. Only one patient tolerated no additions, staying on the unmodified T&H diet. Among 13 patients where a specific food caused >30% baseline FC increase, re-exclusion reduced FC to pre-change levels in 12 (92%). Nutritional analysis showed T&H patients met >90% of Dietary Reference Intakes (DRI) for key macro- and micronutrients, except calcium and potassium. Additionally, 19 (55%) reported improved satisfaction with food-related life compared to the unmodified T&H diet period. Conclusion Overall, 49% of patients whose remission was previously induced by nutritional therapy, successfully maintained deep remission with the whole-food Tasty&HealthyTM diet over 4 months. We show the feasibility of personalized dietary treatment with home kits of FC, allowing for dietary flexibility in most patients. Oral calcium supplement may be needed with T&H.

Background Pediatric onset Crohn disease (pCD) tends to be more complicated with a higher likelihood of requiring intestinal resection surgery. Currently there are no predictive tools for surgery in pCD; risk scores and relative survival analysis are available, but these cannot accurately calculate the probability of surgery in children with CD at an individual level. Aims This study aims to apply machine learning to create an individual survival time distributions (ISD) tool for accurate prediction of bowel resection over time in a novel pCD patient. Methods A prospectively-followed cohort of pCD patients (n= 934) was collected through the Canadian Children Inflammatory Bowel Disease Network (CIDsCaNN) inception cohort (2013-2021). 58 of the 934 pCD patients underwent surgery, while the remaining 876 either did not require surgery by the study’s end, transitioned to adult care, or were lost to follow-up. Surgeries included bowel resections for stricturing or penetrating disease. Clinical, laboratory, and treatment data were compiled into three datasets: baseline, induction (baseline + 10 weeks follow-up data), and longitudinal (baseline + 3 equally spaced follow-up visits with all treatment data). To develop the ISD predictor, we built a learning algorithm that includes maximum relevance minimum redundancy (mRMR) feature selection, Cox Proportional Hazards, and Random Survival Forest models. To estimate the quality of the ISD predictor, measured by the Integrated Brier Score (IBS) and Concordance Index (C-Index), we used k-fold (external) cross validation. Results Our resulted ISD predictors, two trained Cox Proportional Hazards models and one Random Survival Forest model, had IBS scores < 0.1 and C-Index scores > 0.83. These results indicate that our models provide a reliable ranking of survival times based on the individual probability for surgery. The results also showed that the features that are most informative for prediction of surgery were stricturing behavior, penetrating behavior, and distal bowel involvement. Conclusions This study suggests that it is possible to produce an ISD predictor capable of forecasting bowel resection over future times in a novel pCD patient. This novel approach can build tools to improve both the choice and timing of therapy. Funding Agencies CIHRWomen and Children’s Health Research Institute

Abstract Background Ulcerative colitis (UC) is a chronic inflammatory condition of the rectum and colon with a complex aetiology involving genetic, immune, and microbial factors. Less is known about the pre-disease phase of UC compared to Crohn’s disease (CD). Investigating the preclinical biomarkers that precede the development of UC may provide insights into its pathogenesis. Methods Participants were recruited as part of the CCC-GEM project, a prospective cohort study following healthy first-degree relatives (FDR) of patients with CD. Baseline gut inflammation was assessed using faecal calprotectin (FCP), with a cut-off of 100ug/g, while baseline gut permeability was assessed by the fractional urinary excretion ratio of lactulose-to-mannitol (LMR). Baseline faecal microbiome composition was analyzed using 16s rRNA sequences, and functional pathways were inferred using PICRUSt2. Cox proportional hazards models were used to assess the association of baseline variables with UC onset, adjusting for age, sex, and family clustering. Significance was determined using p-values and false discovery rate-adjusted q-values. Results Among 3,596 FDRs, 16 developed UC during a median follow-up of 6.88 years. FDRs with elevated baseline FCP had a 3.1-fold higher risk (p=0.02) of developing UC, while no significant association was observed between baseline LMR and UC onset. The relative abundance of genus Bilophila (HR=0.33 per SD, q=0.010) and Bifidobacteria (HR=0.16, q=0.02) were associated with UC risk, but lost significance after adjusting for FCP. Interestingly, the relative abundances of genera Alistipes (HR=0.15, q=0.0007), Phascolarctobacterium (HR=0.08, q=0.027), Christensenellaceae R.7 group (HR=8.37, q=0.02) and Angelakisella (HR=5.28, q=0.004) remained significantly associated with risk of UC even after adjusting for FCP. Thirty-seven pathways, predominantly involved in specific metabolic processes such as carbohydrates, lipid, or folate metabolism, were also associated with UC risk. Fur example, pathways involving hydroxymethylglutaryl-CoA reductase (HR=0.44, q=0.03), choline monooxygenase (HR=0.22, q=0.005), and 3-phenylpropionate/trans-cinnamate dioxygenase (HR=4.70, q=0.001) remained significantly associated with UC risk even after adjusting for FCP. Conclusion We report that elevated FCP, but not LMR, was significantly associated with future risk of UC. Furthermore, specific microbial taxa and functional pathways exhibited strong associations with future risk of UC, independent of FCP. These microbial signatures were distinct from the previously reported pre-CD microbial changes, suggesting a unique gut microbial contribution to the development of UC. References Raygoza Garay JA, Turpin W, Lee S-H, et al. Gastroenterology 2023;165:670–681.

Abstract Background Exclusive enteral nutrition (EEN) is effective for inducing remission in Crohn's disease (CD) but has adherence challenges. The CD-Exclusion Diet (CDED) is an effective alternative but requires partial enteral nutrition (PEN) with formula and mandatory ingredients. The Tasty&HealthyTM (T&H) diet excludes processed food, gluten, red meat, and dairy (except plain yogurt) without mandatory ingredients or PEN. This randomized controlled trial assessed the tolerability and effectiveness of the T&H diet compared to EEN in children and young adults with CD (NCT#04239248; TASTI-MM, T&H to Induce remission in Mild-Moderate CD). Methods Patients aged 6-25 years with mild-moderate CD were randomized to follow T&H or EEN for 8 weeks, receiving weekly dietary support. The caring physician was blinded to the allocation. Data on nutrition, clinical symptoms, and calprotectin were collected at baseline and bi-weekly. Tolerability was defined as discontinuation of the intervention or low adherence, judged by weekly interviews and 24-hour intake diary. Effectiveness outcomes included clinical remission (wPCDAI/CDAI), MINI index (<8 points reflecting mucosal healing), CRP, ESR, and calprotectin. Those not tolerating either intervention during the first 24 hours were excluded; otherwise, figures reflect intention to treat (ITT) results, unless per-protocol (PP) analyses is specified. Results A total of 83 patients were included (41 to T&H and 42 to EEN; mean age 14.5±3.7 years). The primary endpoint was met with 36 (88%) patients tolerating T&H vs. 22 (52%) tolerating EEN (OR 6.3 (95%CI 2.2-22; p<0.001). Clinical remission was achieved in 56% of the T&H arm and 38% of EEN (p=0.1; PP: 67% vs. 76%, respectively, p=0.47). MINI<8 at week 8 was higher in the T&H arm (54% vs. 41%; p=0.026) while there was no difference in the PP analysis. Calprotectin decreased significantly from baseline in both arms, without a difference across groups at week-8 (calprotectin <250 was noted in 38% with T&H vs 41% with EEN; p=0.84). Similarly, CRP and ESR decreased significantly in both groups (all p<0.05), with no between-group differences in either the ITT or PP analyses. There were 3 adverse events reported in this trial with at least possible association with the intervention, all mild, 2 in the EEN arm (nausea and dizziness) and 1 in the T&H arm (constipation). Conclusion The T&H diet showed comparable effectiveness to EEN for inducing clinical and biological remission in mild-moderate CD but had better tolerability. T&H offers a flexible alternative without the need for PEN.

Host - microbiome interactions are central to Crohn'sdisease (CD) pathogenesis; yet the early metabolic alterations that precededisease onset remain poorly defined. To explore preclinical metabolicsignatures of CD, we analyzed baseline serum metabolomic profiles in a nestedcase-control study within the Crohn's and Colitis Canada - Genetics, Environment, Microbiome (CCC-GEM) Project, a prospective cohort of 5,122 healthyfirst-degree relatives (FDRs) of CD patients. We included 78 individuals wholater developed CD and 311 matched FDRs who remained disease-free. In an untargetedassessment of metabolomic data, we identified 63 metabolites significantlyassociated with future CD risk. Integrative analyses further identifiedmultiple associations between CD-related metabolites and proteomic markers, gutmicrobiome composition, antimicrobial antibody, fecal calprotectin andC-reactive protein. Quinolinate, a tryptophan catabolite, was elevated inindividuals who later developed CD and showed strong positive correlations withC-reactive protein, fecal calprotectin, and C-X-C motif chemokine ligand 9 (CXCL9).In contrast, higher levels of ascorbate and isocitrate were associated withreduced CD risk and were negatively correlated with C-reactive protein and CD-associated proteins.These findings identify several distinct molecular pathways that contribute toCD pathogenesis.