By Clare Murphy
Health reporter, BBC News
Everyone agrees you can still enjoy a steak
A bitter row has broken out between members of the British meat industry and the World Cancer Research Fund over whether red meat increases the risk of bowel cancer. What do we know about this link?
The WCRF says the evidence that red and processed meats increase the risk of colorectal cancer is "convincing", and since 2007 - when it published a major report on lifestyle and cancer - has urged the public to limit their consumption of steak and sausages.
These conclusions, claim an array of organisations representing meat producers, are flawed. They point to a number of independent scientists who have questioned the conviction with which the link between red meat and cancer was presented in the report.
The WCRF has published a list of "minor errors" with the report - some relating to the findings on red meat and bowel cancer - but says it has no intention of altering the conclusions based on an expert panel's review of the scientific literature.
According to the recommendations, red meat should be consumed in modest amounts, and salami and ham should almost always be avoided.
This latest spat is driven by the fact that the government's Scientific Advisory Committee on Nutrition cited the WCRF report in draft conclusions on the impact of cutting red meat on the nation's iron levels.
The WCRF findings, argues the lobby group for the English beef and lamb industry - EBLEX, should not be used as a "point of reference".
But there have already been clashes within the pages of the leading scientific journal on diet and disease.
In a letter last year to the American Journal of Clinical Nutrition, Professor Stewart Truswell of the University of Sydney questioned why several large studies which found no link had been discarded by the panel, and also pinpointed errors in the reporting of data.
In response, the WCRF explained that a series of studies on meat had been omitted because they did not report on red meat specifically, but it did accept some mistakes in the reporting of the data. This did not however "change the overall picture", it stressed.
Many in the scientific community were however taken aback by the findings of a large study into the relationship between diet and cancer, published in the same nutrition journal last year.
The European Prospective Investigation into Cancer and Nutrition-Oxford (EPIC-Oxford), which followed 65,000 people during the 1990s, found that far from being protected from bowel cancer as anticipated, vegetarians in fact displayed a slightly higher incidence of this form of the disease.
It ran counter to the the findings of a previous arm of the EPIC study which suggested that very high levels of red and processed meat consumption - more than two pork chops every day - was associated with a 35% higher risk of bowel cancer when compared with those who rarely ate red meat.
"Our findings did come as something of a surprise. At the simplest level if meat causes colorectal cancer you would expect to see lower rates in the vegetarians, and we didn't," says Professor Tim Key, the epidemiologist who led the Oxford study.
"It's definitely a really tricky area. It's an enigma - nobody knows the truth. We can be much clearer on the relationship between obesity and cancer, or alcohol and cancer, because it's relatively easy to measure these things. Understanding the exact role specific foods play is much harder to quantify.
"There is a lot of evidence for meat, but it's not completely compelling."
It's not no
The WCRF says the Oxford findings on vegetarians could be explained by chance, noting there were only 28,000 non-meat eaters in the study. Vegetarians, it said, may consume fewer dairy products - "and our report found that milk probably reduces risk of bowel cancer".
RED MEAT CONTENT
Medium steak: 145g
Pork chop: 75g
Spaghetti bolognese with beef: 140g
Serving of roast beef: 90g
"We are in the process of reviewing the evidence on meat and bowel cancer and that is expected to be published later this year," says Professor Martin Wiseman, the project director. "But no research has been published since our report to make us question the finding that there is convincing evidence red and processed meat increase risk of bowel cancer."
"It is easy for anyone to find an individual study to support almost any view they wish to hold. But looking at all the research, the evidence linking red and processed meat and bowel cancer is overwhelming."
The WRCF does not in any event advocate a vegetarian diet, or a complete abstention from red meat. In fact its recommendations that people keep within 500g a week - the equivalent of a fair serving of roast beef on five of those days - is not far off average consumption.
Nell Barrie, Cancer Research UK's science information officer, said: "Two of the world's largest studies on diet and cancer have found that people are more likely to develop some cancers, such as bowel cancer, if they eat too much red or processed meat.
"Cutting down on these foods can help to reduce the risk of developing cancer."
But cancer specialist Professor Karol Sikora said those who enjoyed eating red meat should continue to do so.
"We have created a nightmare situation of confusing messages based on very little evidence. Eating red meat in the context of a balanced diet should really not be viewed as a problem.
"Yes, avoid a high calorie, high fat diet - but by all means enjoy that steak."