Maybe red meat isn’t carcinogenic?
Health authorities have told us for years that we should limit our intake of red meat. But a group of experts says research does not fully corroborate claims that red meat increases the risks of colon cancer.
Official Norwegian nutritional recommendations advise limiting the consumption of red meat and processed meat to 500 grams a week.
The advice was issued in the wake of research indicating that these kinds of meat can raise the risk of colon and rectal (colorectal) cancer. The link is convincing, according to a panel of experts established by the World Cancer Research Fund.
But 23 scientists got together in a workshop and reviewed the studies in the field. They published their findings in the journal Meat Science last fall. Their article underscores the uncertainties in the field of nutritional science.
They concluded that research does not definitively say whether red and processed meat are a cause of colorectal cancer. They say that more evidence is needed.
One explanation for why red meat and processed meat could pose a threat is that they contain substances – carcinogens – which can cause DNA mutations, increasing the chances of tumour development.
Another theory is that processed meats – such as bacon, salami, smoked ham and sausages, as well as minced products like hamburger – are damaging because the iron in the muscle fibres of the meat can be activated in the intestines and iron in a free form poses a hazard.
Perhaps there is a direct link between the red meat in Western food culture and an elevated risk for colorectal cancer. But the link seen in studies could also be deceptive, as other factors can be affecting the risk, assert the researchers in Meat Science.
In their article they point out several uncertainties in previous studies.
One is that results vary so much.
Human and animal studies
Some studies of whether eating red meat and processed meat raise the risk of colorectal cancer show just that, whereas others indicate no effect.
Studies on human subjects can have certain failings because they are done on people from the entire world and on both sexes. Maybe the subjects do not always remember what they ate at any given time, the researchers say.
Charting a cancer link to human diets can also take many years and the studies needed to do this are costly to implement. Scientists often circumvent that problem by experimenting on animals, particularly rats and mice.
This provides quicker and cheaper results. But such studies also have their downsides, write the scientists.
Unrealistic animal studies
One of the researchers at the workshop is Bjørg Egelandsdal, who works at the Norwegian University of Life Science’s Department of Chemisty, Biotechnology and Food Science.
She says one objection that the researchers have raised is that studies of the link between the meat and the disease don’t actually say the meat is the cause of the cancer.
Another is that lab-animal studies do not replicate the diet of a meat-eating human.
“The negative results we see in animal models with regard to intestinal cancer are based on a diet that lacks important, essential micro-substances,” she explains.
Uncertainty is not reported
Helle Margrete Meltzer of the Norwegian Institute of Public Health represented Norway in a project group for the Nordic nutritional advisory boards, which was established last year.
“When we issue dietary advice to the public we cannot communicate the uncertainties we see in the scientific community,” she says.
Nevertheless, she does not agree that the recent article about the possible uncertainties in the research on red meat and colorectal cancer should be interpreted as an objection to standard nutritional health recommendations.
“We are quite comfortable with the advice to limit consumption of red and processed meat to 500g per week, given the knowledge presented in the research summaries,” says Meltzer.
“The researchers did not present any new information here, but they did provide useful nuances about the research results on meat and colorectal cancer.”
But for those who now wonder if they should continue to limit their intake of red meat and processed meat to a half kilo a week – should they?
“Yes, I think so.”
So what about red meat?
And why do some studies find an association between red meat and processed meat and the risk of intestinal cancer? The researchers present a few hypotheses in the new article.
Much of what makes up meat is good for us. But the scientists suggest that if our intake of these ingredients exceeds certain limits we can suffer an imbalance in our diet, which in turn creates a risk of cancer in the large intestine or rectum.
If you have a diet which is deficient in calcium and antioxidants, that could make you more susceptible to negative consequences of meat consumption. This is because the substances in the meat are not sufficiently counterbalanced in the intestines.
Certain animal tests indicate that a low-calcium diet with a high intake of red meat can raise the risk of colorectal cancer.
There is also some basis for the belief that having the right intestinal flora can be advantageous in protecting against the damage that can be caused by red and processed meats.
It is also a good idea to get enough fibre from fruit and vegetables.
Another thing to remember is that the way food is cooked can have an influence on cancer risks. Frying and grilling have been linked to the formation of carcinogenic substances. This applies to all meat, however, and is not an argument against eating red meat.
Read the Norwegian version of this article at forskning.no
Translated by: Glenn Ostling
- The role of red and processed meat in colorectal cancer development: A review, based on findings from a workshop. Meat Science. Februar 2014