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Most authoritative ever report on bowel cancer and diet: Links with meat and fibre confirmed

23 May 2011

The most authoritative ever report on bowel cancer risk has confirmed that red and processed meat increase risk of the disease and concluded that the evidence that foods containing fibre protect against bowel cancer has become stronger.

The report, released as part of World Cancer Research Fund/American Institute for Cancer Research’s (WCRF/AICR) groundbreaking Continuous Update Project (CUP), has examined the links between bowel cancer risk and diet, physical activity and weight, and updated the bowel cancer findings of the WCRF/AICR’s 2007 Expert Report, Food, Nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective.

A systematic review of the evidence was carried out by WCRF/AICR-funded scientists at Imperial College London, who added 263 new papers on bowel cancer to the 749 that were analysed as part of the 2007 Report. An independent Expert Panel then reviewed the results and made judgements.

For red and processed meat, findings of 10 new studies were added to the 14 studies analysed as part of the 2007 Report. The Panel confirmed that there is convincing evidence that both red and processed meat increase bowel cancer risk.

WCRF/AICR recommends that people limit consumption to 500g (cooked weight) of red meat a week - roughly the equivalent of five or six medium portions of roast beef, lamb or pork - and avoid processed meat.

The Expert Panel behind the CUP’s judgements also concluded that the evidence that foods containing dietary fibre reduce bowel cancer risk has become stronger since the publication of the 2007 report. They considered the evidence sufficient to strengthen the conclusion that foods containing fibre protect against bowel cancer from “probable” to “convincing”.

The analysis for fibre included adding seven more studies to the existing eight from the 2007 Report, and the result was that the evidence became much more consistent.

This strengthens WCRF/AICR’s recommendation for people to consume a plant-based diet including foods containing fibre, such as wholegrains, fruits, vegetables and pulses such as beans.

The Panel also confirmed that the evidence published since 2007 did not change the judgements that there is convincing evidence that being physically active reduces risk of bowel cancer and that excess body fat – especially around the waist – remains a convincing cause of bowel cancer. There is also convincing evidence that alcohol consumption increases bowel cancer risk in men and it also probably increases risk in women.

Professor Alan Jackson, Chair of the WCRF/AICR Continuous Update Project (CUP) Expert Panel, said: “Our review has found strong evidence that many cases of bowel cancer are not inevitable and that people can significantly reduce their risk by making changes to their diet and lifestyle.

“Because our judgements are based on more evidence than ever before, it means the public can be confident that this represents the best advice available on preventing bowel cancer.

“There has been a lot of debate over the last few years about the strength of evidence that red and processed meat increase risk of cancer. We hope our review can help give clarity to those people who are still confused about the strength of the evidence.

“On meat, the clear message that comes out of our report is that red and processed meat increase risk of bowel cancer and that people who want to reduce their risk should consider cutting down the amount they eat.”

Teresa Nightingale, General Manager of WCRF, said: “Many people feel confused about cancer prevention because it can seem like a new study is published every week that suggests that a new substance either causes or prevents cancer.

“But the CUP takes the latest scientific findings and adds them to the existing body of evidence in a way that ensures our advice takes the latest research into account. This means people can be confident that our recommendations are up-to-date as well as being the most evidence-based information on cancer prevention available anywhere in the world.

“This latest report shows that there is enough evidence to recommend that people can reduce their bowel cancer risk by consuming less red and processed meat and alcohol, having more foods containing fibre, and by maintaining a healthy weight and being regularly physically active. This report confirms that bowel cancer is one of the most preventable types of cancer and we estimate that about 43 per cent of bowel cancers cases in the UK could be prevented through these sorts of changes. That is about 17,000 cases every year.”

Notes to editors:

  • The CUP report on bowel cancer contains the judgements of the Continuous Update Project Expert Panel. It is chaired by Professor Alan Jackson of the University of Southampton and the other members are: Dr Elisa Bandera of the Cancer Institute of New Jersey; Dr David Hunter of Harvard University; Dr Stephen Hursting of the University of Texas; Dr Anne McTiernan of Fred Hutchinson Cancer Research Center; Professor Hilary J Powers of the University of Sheffield; Professor Ricardo Uauy of Instituto de Nutricion y Tecnologia de los Alimentos in Chile and the London School of Hygiene and Tropical Medicine; and Dr Steven H Zeisel of the University of North Carolina. Professor Elio Riboli of Imperial College London is a panel observer and Dr John Milner of the National Cancer Institute is an advisor. Dr Arthur Schatzkin, of the National Cancer Institute, served on the CUP Expert Panel until his death in 2010.
  • The Panel made judgements on the strength of the evidence following a systematic review of the evidence by a team of scientists at Imperial College London led by Dr Teresa Norat.
  • The CUP report on bowel cancer and a summary including the CUP Expert Panel’s conclusions will be available for download from http://www.wcrf.org/cancer_research/cup/index.php
  • The CUP central database is a unique and valuable resource for researchers. Once WCRF/AICR updates the evidence on all cancers, the CUP database will be made accessible to the world’s scientific community.
  • Following an analysis of Dr Norat’s findings, the CUP’s Expert Panel concluded that there is convincing evidence that red meat; processed meat; excess body fat; and abdominal fatness (fat carried around the waist) increase risk of bowel cancer.
  • They concluded there is convincing evidence that regular physical activity reduces risk of colon cancer (the judgement for physical activity does not include rectal cancer). They also concluded that foods containing dietary fibre reduce risk of bowel cancer. The panel also judged that garlic probably reduces risk of bowel cancer.
  • They concluded there is convincing evidence that alcohol increases bowel cancer risk in men. For women, it probably increases risk.
  • They judged that milk probably reduces bowel cancer risk, but WCRF/AICR does not make a recommendation regarding dairy foods because the evidence for overall cancer risk is unclear.
  • The evidence also shows that dietary supplements containing calcium also probably reduce bowel cancer risk, but when this finding is weighed against the totality of evidence on diet and cancer, WCRF/AICR still recommends looking to whole foods to get the nutrients we need, instead of relying on supplements for cancer protection.
  • Red meat refers to beef, pork, lamb and goat – foods like hamburgers, minced beef, pork chops and roast lamb. As a rough guide, 500g of cooked red meat (WCRF/AICR’s recommended weekly limit) equates to 700 to 750g of uncooked red meat.
  • According to the CUP review, eating an extra 100g per day of red meat increases bowel cancer risk by 17%. Roughly speaking, this would mean that the average person’s risk of bowel cancer would increase from five in 100 to six in 100.
  • Processed meat is meat preserved by smoking, curing or salting, or by the addition of preservatives. Examples include ham, bacon, pastrami and salami, as well as hot dogs and some sausages. Hamburgers and minced meats only count as processed meat if they have been preserved with salt or chemical additives. According to the review, eating an extra 100g per day of processed meat increases bowel cancer risk by 36%. Roughly speaking, this would mean that the average person’s risk of bowel cancer would increase from five in 100 to seven in 100.
  • There are set criteria that the evidence has to meet for the Expert Panel to judge that convincing evidence exists. It needs to be robust enough for it to be thought highly unlikely to be modified in the foreseeable future as new evidence accumulates. All the following are also generally required: Evidence from more than one study type; No substantial unexplained heterogeneity within or between study types or in different populations relating to the presence or absence of an association, or direction of effect; Good quality studies to exclude with confidence the possibility that the observed association results from random or systematic error, including confounding, measurement error, and selection bias; Presence of a plausible biological gradient (‘dose response’) in the association. Such a gradient need not be linear or even in the same direction across the different levels of exposure, so long as this can be explained plausibly; Strong and plausible experimental evidence, either from human studies or relevant animal models, that typical human exposures can lead to relevant cancer outcomes.

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    About WCRF

    World Cancer Research Fund (WCRF) raises awareness that cancer is largely preventable and helps people make choices to reduce their chances of developing the disease.

    This includes research into how cancer risk is related to diet, physical activity, and weight management, and education programmes that highlight the fact that about a third of cancers could be prevented through changes to lifestyle. For more information on the charity’s work, visit www.wcrf-uk.org

    The WCRF report, called Food, Nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective, was launched in November 2007 and is the most comprehensive report ever published on the link between cancer and lifestyle. For more information, visit www.dietandcancerreport.org

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