在许多国家，超重和肥胖等状况的患病率逐渐上升，与结直肠癌风险增加相关。然而，许多结直肠癌患者在诊断前会出现体重减轻，这可能导致关联性被低估。通过考虑不同时间框架下的BMI和体重变化来评估BMI和体重变化与结直肠癌风险的关系，并考虑预诊断期体重减轻因素。该人群基础病例对照研究在德国西南部于2003年至2021年间进行。纳入首次诊断结直肠癌和对应年龄、性别和县城匹配的对照组（具有全面的危险因素信息和自我报告的不同时间点的体重）。数据分析于2022年10月至2023年3月间进行。分析不同时间框架（诊断前或招募时）BMI和体重变化与结直肠癌之间的关联，通过多变量logistic回归进行全面混杂因素调整。共纳入11,887名参与者（6434名结直肠癌病例，5453名对照组；中位数年龄（IQR）为69[61-77]岁；7173名男性[60.3%]）。在诊断时，3998例（62.1%）病例和3601例（66.0%）对照组超重或肥胖，暗示过量体重与结直肠癌风险呈负相关。相反，当使用8至10年前测量的BMI时，我们发现超重（调整后的比值比[aOR]为1.27；95% CI，1.03-1.56）、肥胖（aOR为2.09；95% CI，1.61-2.70）和BMI5单位增加（aOR为1.35；95% CI，1.21-1.50）与结直肠癌风险显著正相关。随着在诊断前的早期时间间隔的考察，高BMI作为结直肠癌风险因素的关联性也随之增强，使用至少在诊断前8年的BMI时，关联性尤为显著。与结直肠癌的关联性相反，体重减轻（达到或超过2公斤）的关联性存在反向趋势，减重在诊断前2年内的效应最大（aOR为7.52；95% CI，5.61-10.09），并逐渐降低。在这个基于人群的病例对照研究中，考虑大量的预诊断期体重减轻进一步突出了超重和肥胖与结直肠癌风险的关联。

Overweight and obesity, conditions with rising prevalence in many countries, are associated with increased colorectal cancer (CRC) risk. However, many patients with CRC lose weight before diagnosis, which may lead the association to be underestimated.To evaluate the association of body mass index (BMI) and weight change with CRC risk when considering BMI at different time frames, with the intention to account for prediagnostic weight loss.This population-based case-control study was conducted in southwestern Germany between 2003 and 2021. Cases with a first diagnosis of CRC and controls (frequency matched by age, sex, and county) with comprehensive risk factor information and self-reported weight at different time points were included. Data were analyzed between October 2022 and March 2023.BMI and weight change at different time frames before the time of diagnosis (cases) or recruitment (controls).Association of BMI and weight change at various points in time before and up to diagnosis with CRC, assessed by multivariable logistic regression with comprehensive confounder adjustment.A total of 11 887 participants (6434 CRC cases, 5453 controls; median [IQR] age, 69 [61-77] years; 7173 male [60.3%]) were included. At the time of diagnosis, 3998 cases (62.1%) and 3601 controls (66.0%) were overweight or obese, suggesting an inverse association between excess weight and CRC risk. Conversely, we found significant positive associations of overweight (adjusted odds ratio [aOR], 1.27; 95% CI, 1.03-1.56), obesity (aOR, 2.09; 95% CI, 1.61-2.70), and a 5-unit increase in BMI (aOR, 1.35; 95% CI, 1.21-1.50) with CRC risk when using BMI measured 8 to 10 years before diagnosis. High BMI as a risk factor for CRC was increased as earlier periods before diagnosis were examined, with the association being particularly pronounced using BMI at least 8 years before diagnosis. An opposite trend was found for the association of weight loss (at or exceeding 2 kg) with CRC, with the greatest effect sizes occurring for weight loss within 2 years before diagnosis (aOR, 7.52; 95% CI, 5.61-10.09), and gradually decreased for earlier intervals.In this population-based case-control study, accounting for substantial prediagnostic weight loss further highlighted the association of overweight and obesity with CRC risk.