Comment on ‘Impact of perioperative nutrition on recovery after radical cystectomy: a randomised trial’

We read with great interest the randomised controlled trial by Amer et al. [1], which demonstrated that perioperative nutritional optimisation accelerated gastrointestinal recovery, reduced length of stay, and improved bioimpedance-derived cellular health following radical cystectomy. This work is timely, given the increasing emphasis on metabolic resilience and enhanced recovery pathways in cystectomy care, and we commend the authors for undertaking a well-designed prospective study in a complex surgical population. Nevertheless, several methodological aspects merit further clarification to strengthen the interpretability and translational potential of the findings. First, although the sample size was powered based on a hypothesised reduction in 30-day complications, the primary endpoint did not reach statistical significance, whereas several secondary endpoints showed improvement. This introduces the risk of primary outcome drift, whereby conclusions are inferred from secondary measures that were not the basis of the original power calculation. As perioperative complication rates remain the clinically recognised benchmark for defining the success of cystectomy pathways, a recalibration of the primary endpoint—or hierarchical testing to control inferential direction—would help align the statistical design with the study's final message [2]. Second, the intervention administered to the nutrition optimisation group constituted a composite bundle comprising immunonutrition, anaemia and micronutrient correction, carbohydrate loading, structured dietary supervision, and postoperative feeding strategies. While such a multimodal approach reflects real-world nutritional practice, its multicomponent nature limits causal attribution. The observed improvements cannot be ascribed to any single element, nor can it be determined whether the magnitude of benefit stemmed from the biochemical content, the behavioural counselling, or the duration of exposure. Future factorial or multi-arm designs would enable disentanglement of these components and identify the elements most responsible for clinical benefit [3]. Third, the trial reports complete retention and intervention completion, with no withdrawals, loss to follow-up, or recorded deviations from the nutritional protocol. Such perfect adherence is seldom achievable in perioperative settings characterised by variable tolerance, appetite fluctuations, and psychosocial barriers, particularly over a 4–6-week perioperative window. The absence of adherence metrics limits reproducibility and raises concerns regarding external validity, as the observed effect size may be partly attributable to study-team oversight rather than a scalable intervention applicable across diverse institutions [4]. Fourth, the significant improvement in preoperative serum albumin in the intervention group warrants a more granular temporal analysis. Because patients commenced nutritional optimisation at variable time points before surgery, exposure duration cannot be disentangled from treatment effect, introducing a time-dependent exposure bias. Standardising the intervention period or stratifying outcomes by exposure length would clarify whether albumin elevation reflects the intervention itself or simply longer nutritional exposure. In summary, Amer et al. [1] have contributed important evidence supporting the role of perioperative nutritional strategies in accelerating recovery after radical cystectomy. Addressing the issues of endpoint alignment, causal attribution, adherence reporting, and exposure standardisation would further enhance the methodological robustness and facilitate broader clinical adoption. We look forward to future studies that refine these elements and help transform perioperative nutrition from a supportive adjunct into a reproducible, evidence-based therapeutic pathway. The authors declare no conflicts of interest.