Inflammatory bowel disease (IBD), encompassing Crohn's disease (CD) and ulcerative colitis (UC), significantly impacts health-related quality of life (HRQoL) and physical activity (PA), often accompanied by undernutrition. Malnutrition, characterized by an imbalance of energy, protein, and other nutrients, leads to adverse effects on body composition (BC), including lean mass loss and skeletal muscle mass (SMM) reduction, even with normal BMI. This SMM loss increases sarcopenia risk, predicting poor outcomes, relapse, surgery needs, and reduced biological efficacy in children with IBD. Malnutrition and impaired BC contribute to decreased HRQoL. Physical activity (PA) is positively associated with HRQoL and lean body mass. Elevated TNF-α levels are involved in skeletal muscle loss and growth impairment; anti-TNF therapy might positively affect sarcopenia by inhibiting inflammation and catabolism. The interplay between BC, HRQoL, and PA warrants investigation. Prior research lacked longitudinal studies on pediatric IBD patients undergoing biological therapy. This study aimed to assess changes in BC, HRQoL, and PA in children with IBD starting anti-TNF therapy and compare BC and PA to healthy controls. A secondary aim was to analyze baseline characteristics of patients with or without sarcopenia risk and track BC changes.

Existing literature highlights the negative impact of IBD on nutritional status and physical function. Studies show a strong correlation between malnutrition, specifically sarcopenia, and poorer clinical outcomes in IBD patients. The loss of lean body mass and skeletal muscle mass is a significant concern, influencing treatment response and overall prognosis. Previous research suggests a potential beneficial role for anti-TNF therapy in mitigating muscle loss in adults, but this remains understudied in pediatric populations. The relationship between body composition, physical activity levels, and health-related quality of life is complex and needs further investigation, particularly in children with IBD undergoing anti-TNF treatment. A limited number of cross-sectional studies have examined these factors in children with IBD, but longitudinal data are lacking.

This prospective, observational, single-center cohort study recruited 32 pediatric IBD patients (21 with CD, 11 with UC) initiating anti-TNF therapy (October 2016-December 2018). Inclusion criteria were age 10-19 years and informed consent; exclusion criteria included conditions affecting BC, PA, or HRQoL. Diagnosis was based on Porto criteria; anti-TNF therapy was indicated by Hungarian National Health Insurance Fund criteria and international guidelines. A control group of 307 healthy children (10-18 years) was included for BC and PA comparisons. Body composition was assessed using bioelectrical impedance analysis (InBody 720) at baseline (M0), 2 months (M2), and 6 months (M6). Physical activity was measured using adapted PAQ-C and PAQ-A questionnaires. HRQoL was assessed using the Hungarian-adapted Canadian IMPACT-III questionnaire. Disease activity was assessed using PCDAI and PUCAI scores. Data analysis involved Z-score conversion for height, weight, and BMI using Hungarian reference data. LMS method generated reference values for BC parameters from the control group. GLM and Friedman tests were applied to analyze changes in BC, PA, and HRQoL. Subgroup analysis compared patients with and without sarcopenia risk (baseline SMM Z-score ≤ -1).

During the six-month anti-TNF therapy follow-up, CD patients showed a significant increase in fat-free mass Z-score (-0.3 at baseline to 0.1 at M6, p=0.04). In contrast, UC patients showed no significant changes in BC parameters. CD patients had lower PA at baseline (1.1 vs. 2.4 in controls) but this difference disappeared by M6 (2.3 vs. 2.4). UC patients' PA was comparable to controls at baseline and remained unchanged. HRQoL, as measured by IMPACT-III, did not show significant changes in either group. Subgroup analysis comparing patients with and without sarcopenia risk (baseline SMM Z-score ≤ -1) revealed that those at risk were younger and shorter at baseline. However, their SMM Z-score significantly increased during the follow-up. There was a correlation between IMPACT-III and PAQ scores at baseline in CD patients (r=0.73, p=0.007).

This study demonstrated a positive effect of anti-TNF therapy on fat-free mass in CD patients, but not in UC patients. This aligns with findings suggesting that BC deficits in CD may result from immune-mediated mechanisms affecting growth hormone metabolism, which are modulated by anti-TNF therapy. The lack of significant HRQoL or PA improvements might reflect the need for longer treatment durations or other interventions. The baseline characteristics of patients with sarcopenia risk highlight the vulnerability of younger children with IBD. Weight and BMI were not sensitive enough markers of nutritional status compared to fat-free mass. The study's findings underscore the importance of ongoing nutritional monitoring and interventions to improve outcomes.

Anti-TNF therapy positively influenced fat-free mass in pediatric CD patients but not in UC patients. While weight and BMI were not sensitive enough to reflect nutritional status, fat-free mass changes were observed in CD patients. No significant improvements in HRQoL or PA were noted, suggesting the need for longer-term observation. The vulnerability of younger children with lower SMM Z scores was highlighted. Comprehensive nutritional monitoring and promoting physical activity are crucial for children with IBD.

The study's limitations include a relatively small sample size, a short follow-up period, and the lack of detailed dietary intake data. The absence of functional muscle parameter assessments (like grip strength) limits the comprehensive evaluation of muscle function. The single-center design might limit the generalizability of findings. Further research with larger samples, longer follow-up periods, and comprehensive dietary assessments is warranted.