英国医生研究了近3万癌症病例后发现，体重超标将提升20多种癌症的发病率。领导这项研究的科学家，英国曼彻斯特大学的安德鲁-雷内汉（Andrew Renehan）将研究结果发表在了著名医学杂志《柳叶刀》杂志上。
与此同时，在美国波士顿召开的美国科学促进会的年会上，哈佛大学公共卫生学院的营养专家沃尔特-维列特（Walter Willett ）预言，肥胖将迅速取代吸烟，成为首要的致癌因素，尤其是在发展中国家。他列举了很多例子——既有动物试验也有人体试验，有些已经完成有些还在进行中，而这些例子都证明，维列特的预言绝非信口开河。
维列特说：“目前，至少有20％的癌症与肥胖有关，吸烟导致的癌症则占所有癌症的30％左右，肥胖与吸烟的致癌率越来越接近。但在美国，吸烟的人已经越来越少，而肥胖人数却在迅速增加，因此，要不了多久，肥胖的致癌率就会超过吸烟的致癌率。“
曾有研究表明，当一个人到了75岁，或者更大年龄时，稍微长胖点有助延长寿命，降低死亡几率。不少科学家认为，上述结论其实并没有科学依据，但还是有医生给出了“合理”的解释：如果一个老人偏瘦，说明他正受到疾病的困扰，体重稍微超标，则有助于抵抗一些常见疾病。
2006年，美国南加利福尼亚大学的科学家做了一项研究，他们发现在80岁以上的老年人中，体重稍微超标的人，死亡率比其他老年人更低。但在同一项研究中，在20岁出头的年轻人中，体重超标或肥胖的人，死亡率却是同龄人中最高的。
这项研究的关键在于，老年人应该超重多少最合适？遗憾的是，他们并没有找到答案，因为在80岁以上的老年人中，几乎没有肥胖者了。
的确，多长肉有助于癌症患者抵抗化疗等带来的创伤，但对于任何人来说，不患癌症可能更实际也更令人高兴，而达到这个目标的第一件事，就是保持苗条的身材。
不过需要注意的是，瘦只能降低患癌几率，而不是完全排除这种可能性。如果不相信本文的观点，可以去找找看，有没有90多岁的肥胖老人。
生物谷推荐原始出处：
The Lancet 2008; 371:569-578
DOI:10.1016/S0140-6736(08)60269-X
Body-mass index and incidence of cancer: a systematic review and meta-analysis of prospective observational studies
Dr Andrew G Renehan PhD, Margaret Tyson PhD, Matthias Egger MD, Richard F Heller MD and Marcel Zwahlen PhD
Summary
Background
Excess bodyweight, expressed as increased body-mass index (BMI), is associated with the risk of some common adult cancers. We did a systematic review and meta-analysis to assess the strength of associations between BMI and different sites of cancer and to investigate differences in these associations between sex and ethnic groups.
Methods
We did electronic searches on Medline and Embase (1966 to November 2007), and searched reports to identify prospective studies of incident cases of 20 cancer types. We did random-effects meta-analyses and meta-regressions of study-specific incremental estimates to determine the risk of cancer associated with a 5 kg/m2 increase in BMI.
Findings
We analysed 221 datasets (141 articles), including 282?137 incident cases. In men, a 5 kg/m2 increase in BMI was strongly associated with oesophageal adenocarcinoma (RR 1·52, p<0·0001) and with thyroid (1·33, p=0·02), colon (1·24, p<0·0001), and renal (1·24, p <0·0001) cancers. In women, we recorded strong associations between a 5 kg/m2 increase in BMI and endometrial (1·59, p<0·0001), gallbladder (1·59, p=0.04), oesophageal adenocarcinoma (1·51, p<0·0001), and renal (1·34, p<0·0001) cancers. We noted weaker positive associations (RR <1·20) between increased BMI and rectal cancer and malignant melanoma in men; postmenopausal breast, pancreatic, thyroid, and colon cancers in women; and leukaemia, multiple myeloma, and non-Hodgkin lymphoma in both sexes. Associations were stronger in men than in women for colon (p<0·0001) cancer. Associations were generally similar in studies from North America, Europe and Australia, and the Asia–Pacific region, but we recorded stronger associations in Asia–Pacific populations between increased BMI and premenopausal (p=0·009) and postmenopausal (p=0·06) breast cancers.
