虽然高身体质量指数（BMI）与患结肠直肠癌（CRC）的风险增加相关，但许多CRC患者在诊断前体重下降。BMI常常在接近诊断时报告，可能会导致低估或甚至颠倒BMI-CRC的关联方向。我们的目标是评估可能来自诊断前体重减轻的偏差在可用流行病学证据中是否得到考虑以及考虑到了多少程度。我们在PubMed和Web of Science上搜索了系统性回顾和荟萃分析，直至2022年5月，以研究BMI-CRC相关性。提取有关设计方面和结果的信息，包括回顾是否以及如何处理诊断前体重减轻作为潜在偏差来源。此外，我们分析了包含在最新系统性回顾中的个体队列研究如何处理这个问题。总体上，我们发现了18个回顾。其中没有一个系统地考虑或讨论诊断前体重减轻作为潜在偏差来源。在最新回顾中纳入的21个队列中，大多数（15/21）没有将任何起始的随访年限从其主要分析中排除。尽管大多数研究报告表示已经进行了敏感性分析，在这些分析中排除了起始的随访年限，但结果报道非常异质性，且大多仅排除了1-2年。在明确报告的情况下，影响估计值通常随着排除年限的增加而增加。超重和肥胖对CRC风险的影响可能比现有的流行病学证据所暗示的更大。©2023年。作者（们）。

Although high body-mass index (BMI) is associated with increased risk of developing colorectal cancer (CRC), many CRC patients lose weight before diagnosis. BMI is often reported close to diagnosis, which may have led to underestimation or even reversal of direction of the BMI-CRC association. We aimed to assess if and to what extent potential bias from prediagnostic weight loss has been considered in available epidemiological evidence. We searched PubMed and Web of Science until May 2022 for systematic reviews and meta-analyses investigating the BMI-CRC association. Information on design aspects and results was extracted, including if and how the reviews handled prediagnostic weight loss as a potential source of bias. Additionally, we analyzed how individual cohort studies included in the latest systematic review handled the issue. Overall, 18 reviews were identified. None of them thoroughly considered or discussed prediagnostic weight loss as a potential source of bias. The majority (15/21) of cohorts included in the latest review did not exclude any initial years of follow-up from their main analysis. Although the majority of studies reported having conducted sensitivity analyses in which initial years of follow-up were excluded, results were reported very heterogeneously and mostly for additional exclusions of 1-2 years only. Where explicitly reported, effect estimates mostly increased with increasing length of exclusion. The impact of overweight and obesity on CRC risk may be larger than suggested by the existing epidemiological evidence.© 2023. The Author(s).