Red meat increases risk of colorectal cancer
BMJ 2005; 330 doi: https://doi.org/10.1136/bmj.330.7505.1406-b (Published 16 June 2005) Cite this as: BMJ 2005;330:1406All rapid responses
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The research team (Norat et al) makes an interesting comment on
association between heme iron and cancer risk, which is thought to be able
to explain why red meat increases cancer risk while poultry does not.
however in my view, it is also possible that cattle breeding method and
condition also contribute to this increase. the grass where the cattle are
fed might be contaminated by pesticides, and the cattle might have been
injected a drug (either to improve the quality of meat or to cure the
disease) which might be carcinogenic.
i'd like to underscore another rapid response though, which questions
whether red meat itself really has something to do with higher risk of
cancer. i agree that it is the processing method which matters (especially
when nitrites or nitrates are added). but the problem is not merely the
meat itself; probably the loss of plant-based foods from our daily diet
would better describe it. these products, which are protective against
cancer, have been replaced by meat. and the drawback is:
a number of people, while eating more meat, tend to skip plant-based
foods so they consume less fibre (as the authors mention) and, i think,
less antioxidants as well. this means that less protective substances are
available in the body to prevent carcinogenesis, and the result is a
higher risk of cancer.
Competing interests:
None declared
Competing interests: No competing interests
The tlitle 'Red meat increases risk of colorectal cancer' is ok, as
in many situations it is hard to say something clear in a sentence,
especially in medical area, causal relationships are always based on many
condictions and assumptions. For example as drinking large amount of water
within a short time may put somebody's life at threat especially among old
people who do not necessary have good renal function. Is it suitable for
the media to encourage the public to drink more water in hot weather
adding that 'drinking large amount of water within short time may be
harmful' ?
However as the public gets the access to the lastest medical
information, suitable guideline for the public to read/'face' medical news
or literature may need to be promoted in order to prevent negative
impacts may caused by some studies such as impacts caused by the study
about MMR vaccine and autism.
Competing interests:
None declared
Competing interests: No competing interests
A study that associates increased risk of colorectal cancer with
increased consumption of red and processed meat should not be entitled,
"Red meat increases risk of colorectal cancer." The potential danger of
processed meat should not be ignored.
We live in an age where many people glance at headlines without
finding the time to read the adjoining articles. A responsible publishing
team such as that at the BMJ should not take lightly the importance of
carefully written headlines.
Competing interests:
None declared
Competing interests: No competing interests
There are a number of points that this study raises which it doesn't
answer.
We, as a species have been eating red meats for several thousands of
years - without any history of colon cancer. Many peoples in the world
still do. So why should they be carcinogenic now?
Table 2A of the study shows that red meat intake does not increase
the risk in Aarhus and Potsdam (HR=1.00) and it is protective in Italy
(HR=0.96). In the other countries, there is a slight increase (HR=1.01-
1.04). So in some countries eating red meat seems to be harmful, in
another it is beneficial, and in others it has no effect one way or the
other
95% confidence intervals all cross 1.00, so some of the subjects in
all centres used in this trial benefitted from eating red meat even in
those countries where it appeared to increase the risk.
All these countries have different dietary cultures and even people
within them eat different foods and combinations of foods. They also will
prepare, store and process them in different ways. As the numbers are all
pretty close to 1.00 (which would indicate no effect one way or the
other), I suspect that they are merely artifacts which have little if any
practical meaning, particularly as lumping fresh meats and processed meats
together makes a nonsense of the whole exercise.
And the authors do admit that:
"Our study has several limitations. Most important, methods used in
nutritional epidemiology are known to provide imprecise estimates of food
intake. Random measurement errors of food intake lead to the attenuation
of the disease risk estimates"
So any or all of those could be the answer.
Will I cut down on red meat? No! Although, having said that, I tend
not to eat processed foods
And there is one other confounding factor: It has been shown many
times over the last century that lean meat is not as healthy as fat meat.
The Italians might have benefitted because they eat a lot more animal fat
than we do.
So, the real message might actually be that we should eat fat meat to
prevent colon cancer. Just a thought.
Competing interests:
None declared
Competing interests: No competing interests
Cohort study, Correlation, and Causality
Dear editor,
The cohort study about the association between red meat, processing
meat, fish consumption and the risk of developing colorectal cancer, has a
huge cohort, excellent methods to measure exposure, incident, and great
data collect and analyse methods[1] Moreover I feel it is one of the best
cohort studies.
The contribution of this cohort study would be confirming a direction
for further investigation, and providing strong evidence supporting that
there is association between red meat/ processing meat consumption and the
risk of developing colorectal cancer among humans.
However causal relationships are unable/ unrealistic to be
established based on only non-experimental studies even they are
perfect(technically non-experimental study can never be perfect). Cohort
studies as well as other non—experimental studies do have their limit. For
example, if people who are genetically more likely to develop colorectal
cancer, genetically prefer the taste of red meat/ processing meat rather
than the taste of any other food—'food preference and higher risk of
developing colorectal cancers are brothers rather than son and dad'.
Though this explanation is hardly based on any ground but logically the
result of the cohort study does also support this ‘hypothesis’.
Thus I believe it would be a good idea for the public to have such an
idea that causal relationships can not be proved by cohort studies, case-
control studies and other non-experimental studies.
Reference
1 Norat, T. et al Meat, Fish, and Colorectal Cancer Risk: The
European Prospective Investigation into Cancer and Nutrition Journal of
the National Cancer Institute, 2005 Vol. 97, No. 12.
Competing interests:
None declared
Competing interests: No competing interests