By Madlen Davies
Red meat may be linked with cancer because it contains a chemical that is unnatural to the human body, scientists say.
Previous studies have linked red-meat consumption to a number of cancers, especially colorectal, breast, prostate, ovarian and lung cancers.
Now, U.S. researchers believe the culprit is a sugar molecule called Neu5Gc, found in beef, pork and lamb.
When eaten, the body sees it as a foreign substance – and the immune system attacks it.
This leads to inflammation in the body, which over time is known to promote the formation of tumours.
Red meat is linked with cancer due to a sugar molecule called NeuG5c. This is unnatural to the human body, and so the immune system attacks it. This leads to inflammation, which over time causes tumours to form
The same process could happen when people drink whole milk, certain cheeses and fish eggs, which all contain Neu5Gc, the researchers warned.
As Neu5Gc naturally occurs in most mammals but not humans, this also explains why humans are more at risk cancer while other carnivores are not.
The research is significant as it diverges from the previously held theory about red meat and cancer.
Previously it was believed there was an association between red meat and cancer because of the carcinogenic chemicals linked to grilling.
But grilling fish and chicken generates the same carcinogenic molecules as grilling red meat and yet they are not associated with a risk of cancer.
Scientists said the fact that they have very little or no Neu5Gc could now explain why.
Dr Ajit Varki, from the University of California San Diego, who led the study, said the Neu5Gc phenomenon is unprecedented.
He said: ‘In this case, the foreign sugar is like a Trojan Horse. It becomes part of your own cells.’
‘When you react to a peanut or other allergy-causing substance, you’re reacting to something foreign.
‘This is the first example we know of something that’s foreign, gets totally incorporated into you despite the fact that your immune system recognises it.’
However, Dr Varki said Neu5Gc plays the role of ‘gasoline on the fire’.
That is, it boosts the cancer risk, but doesn’t seem to be the ultimate cause of the disease.
As part of the study, Dr Varki and his colleagues fed Neu5GC to two groups of mice.
One group naturally had Neu5Gc and another was genetically engineered to no longer have the molecule, mimicking human biology.
The specially engineered mice showed a cancer rate that was more than five times that of the other rodent group.
They were not exposed to carcinogens, further implicating Neu5Gc as a key link between red meat and cancer.
Dr Varki added: ‘Until now, all of our evidence linking Neu5Gc to cancer was circumstantial or indirectly predicted from somewhat artificial experimental setups.
‘This is the first time we have directly shown that mimicking the exact situation in humans – feeding non-human Neu5Gc and inducing anti-Neu5Gc antibodies – increases spontaneous cancers in mice.
‘The final proof in humans will be much harder to come by.
‘But on a more general note, this work may also help explain potential connections of red meat consumption to other diseases exacerbated by chronic inflammation, such as atherosclerosis and type 2 diabetes.’
He does not advise cutting red meat out of the diet, however.
It comes after the World Cancer Research Fund advised eating no more than 500g of red meat per week – the equivalent of five or six medium portions of roast beef, lamb or pork. They also advise eating processed meats like bacon, ham and salami as little as possible
Dr Varki continued: ‘Of course, moderate amounts of red meat can be a source of good nutrition for young people.
‘We hope that our work will eventually lead the way to practical solutions for this catch-22.’
In fact, selective breeding could allow farmers to reduce the amount of NEu5Gc in meat, and it may be possible to develop an antidote to counteract the cancer risk.
The study was published online in the Proceedings of the National Academy of Sciences.
It comes after the World Cancer Research Fund advised eating no more than 500g of red meat per week – the equivalent of five or six medium portions of roast beef, lamb or pork.
It also advised eating processed meats like ham, bacon and salami as little as possible.
‘Convincing evidence’ that both types of meat increase the risk of bowel cancer – as well as other cancers – means people should seriously think about cutting down, it recommended.