Eating lots of red meat is linked with DNA damage which raises the risk of bowel cancer, researchers suggest.
There are health concerns over red meat
Scientists at the MRC Dunn Human Nutrition Unit and the Open University compared red meat and vegetarian diets.
Their study, published in Cancer Research, found the red meat diet was associated with a higher level of DNA damage.
Previous work suggests regular meat eaters are significantly more likely to develop bowel cancer.
Almost 17,000 people die from the disease each year.
Last year the Dunn team published a study suggesting the chance of developing the disease was a third higher for people who regularly ate more than two portions per day of cooked red meat compared with those who ate less than one portion per week.
In the latest study the same Dunn team examined cells from the lining of the colon taken from healthy volunteers eating different diets.
They found higher levels of DNA damage in the cells taken from people eating red meat.
Work by the Open University team suggests the reason could be the presence of substances called N-nitrosocompounds, which form in the large bowel after eating red meat.
Their work suggests that these compounds combine with DNA, and alter it so that it is more likely to undergo harmful changes or mutations that increase the likelihood of cancer
Professor David Shuker, head of the Open University team, said: "These combined discoveries have allowed us to link red meat consumption to an increased risk of bowel cancer and may give us some clues about developing a screening test for very early changes related to the disease."
'Moderation is key'
Professor Colin Blakemore, chief executive of the Medical Research Council, which funded the research, said: "Large bowel cancer is the second most common cancer in western countries and nearly one million cases occur each year worldwide.
"This latest study, together with the compelling epidemiological evidence published last year, is an important step towards understanding, and potentially preventing this common disease."
A spokesman for the charity Beating Bowel Cancer said: "The fact is a third of all cancers are linked to what we eat and we must not underestimate the importance of a well-balanced diet in the prevention of bowel cancer.
"This study certainly seems to add further weight to previous evidence about the possible link between bowel cancer and a high consumption of red meat.
"As with all dietary advice, moderation is key as we already know that a diet high in fat and red meat yet low in fibre, fruit and vegetables can increase the risk of developing this disease - currently the second biggest cause of cancer death in the UK."
Professor Annie Anderson, expert advisor to Bowel Cancer UK, said: "The new data not only provides further evidence of risk but also flags the importance of what we eat with our meat - for example, there is further risk with low fibre intakes.
"Current data on eating trends suggests we are eating more fast foods, which we know are high in calories and fat and implicated as a cause of obesity and diabetes, but such cuisine may also be the very type of meals (high in meat - and meat products - and low in vegetables) that also contributes to bowel cancer risk."
But a spokesman for the Meat and Livestock Commission said: "The results of this very small-scale study merely suggest a mechanism by which red and processed meat might possibly increase an individual's risk of developing colorectal cancer.
"The authors themselves acknowledge that larger-scale, prospective studies are needed to identify how important and robust this suggested mechanism could be."