Meat and cancer: Making sense of the evidence
The risk of developing cancer arises from chemicals produced by processing the meat and from cooking.
JOHANNESBURG - Last
week the World Health Organisation's (WHO) cancer arm, the International Agency
Vikash Sewram, the Director of the African Cancer Institute at Stellenbosch
University's Faculty of Medicine and Health Sciences, who also chairs the South
African Ministerial Advisory Committee on the Prevention and Control of Cancer, tackles the link between cancer and some meat.
WHO MADE THE EVALUATION?
assessment was part of the IARC's Monographs Program that has been involved
since 1971 in evaluation of carcinogenic risks to humans whether it be exposure
to chemicals, complex mixtures, biological agents, occupational exposures or
1000 agents have been evaluated in order to identify the potential risks to
human health that exist in the environment. The evaluation of a risk factor
takes place over a period of time and entails interdisciplinary working groups
of expert scientists, selected from all over the world, reviewing published
studies and evaluating the weight of the evidence that an agent can increase
the risk of cancer. A meeting is convened to deliberate the results of the
evaluation based on the evidence at hand.
process is extremely rigorous and representatives from national agencies as
well as industry observers sit in discussions to ensure that the evaluation
process is robust, fair and without any conflicts of interest.
evidence has been evaluated and a consensus reached, the agent is classified
into one of five categories: Group 1: carcinogenic to humans; Group 2A:
probably carcinogenic; Group 2B: possibly carcinogenic; Group 3: not
classifiable as to its carcinogenicity; and Group 4: probably not carcinogenic
481 agents have been identified as either carcinogenic, probably carcinogenic,
or possibly carcinogenic. This information and authoritative review of the
evidence is important, as it allows national health agencies in countries to
use this information as scientific support for their actions to prevent
exposure to potential carcinogens.
MEAT AND CANCER RISK: WHAT THE EVIDENCE SHOW
evaluated two types of meat: processed meat (e.g. meat that has been
transformed through salting, curing, fermentation, smoking or adding of
preservatives) and red meat (beef, lamb, pork, veal, mutton, horse and goat).
working group of 22 experts from 10 countries evaluated the evidence from 800
studies and found that processed meat is carcinogenic to humans (Group 1), as
there is sufficient evidence from epidemiological and mechanistic studies from
around the world that show processed meat consumption causes colorectal cancer.
Red meat consumption was classified as probably carcinogenic to humans (Group 2A) based
on limited epidemiological evidence in humans, although there was strong
evidence to support mechanistic events leading to cancer.
statistically significant dose-response relationship was found where for each
50 gram portion of processed meat eaten per day, the risk of developing cancer
increased by 18 percent. However the risk following a 100 gram portion intake
of red meat per day increased by 17 percent.
classification of processed meat falls into the same category as alcohol,
tobacco smoke, asbestos, HIV, etc. However, it is important to note that all of
these agents, whilst in the same group, do not all share the same level of
hazard. For example, the risk of developing cancer as a result of smoking or
being exposed to second-hand tobacco smoke is many orders of magnitude higher
than that associated with eating red meat. And an HIV-positive person has a
greater risk of developing an AIDS-related cancer, than the risk of developing
cancer from consuming meat.
WHY IS THERE A LINK BETWEEN MEAT INTAKE AND CANCER?
of developing cancer arises from chemicals that are produced by processing the
meat and from cooking. For example, cooking at high temperatures or placing meat
in direct contact with a flame can produce certain types of chemicals that can
damage the DNA. These chemicals are known as carcinogens. A few possible
explanations for the link with processed foods are as follows:
1.Preservatives contain chemicals, known as
nitrates, that are added to some processed meats and have been shown in some
studies to produce N-nitrosamines during cooking - molecules that cause cancer.
2.The smoking process leads to the meat being
contaminated with carcinogenic chemicals from the smoke itself, known as
polycyclic aromatic hydrocarbons (PAHs).
3.When meat is cooked at high heat, PAHs and
other carcinogenic chemicals known as heterocyclic aromatic amines (HAA), are
formed and these chemicals damage DNA. Pan-frying, grilling or barbecuing
produces the highest amounts of these chemicals.
STOP OR CONTINUE EATING MEAT?
decision to stop eating meat is a personal choice. Meat is a good source for
protein, contains all the essential amino acids, is rich in iron, zinc, and
selenium and contains vitamins A, B and D. Conversely, processed and red meat
is relatively high in saturated fat and cholesterol, which are linked to
increased risk of heart disease.
are advised to moderate their meat intake. Regularly eating large portions of
red and processed meat over a long period of time is not advisable. A balanced
diet combined with fruits, vegetables and fibre and regular exercising is the
goal for a healthy life.
priorities for the prevention of cancer and other non-communicable diseases
remain smoking cessation, reduction of alcohol intake, maintenance of normal
body weight and balanced nutrition.
COLORECTAL AND PROSTATE CANCER IN SA: WHAT THE STATISTICS TELL US
latest data from the National Cancer Registry reveals that prostate cancer
remains high on the list of cancers, with an incidence rate of 29.90 per
100 000. One in 27 males will develop prostate cancer in their lifetime.
cancer features much lower with an incidence rate of 7,55 and 4,77 per 100,000
in males and females respectively. This translates to one in 114 males and one
in 182 females developing colorectal cancer in their lifetime.
cancer is most common in the Caucasian population, whilst colorectal cancer is
high among the Caucasian and Asian populations.
meat intake is just one way of minimising risk. Whilst primary prevention
continues to be advocated, early detection remains the mainstay for successful
treatment and outcomes.