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Meat and cancer: Making sense of the evidence

The risk of developing cancer arises from chemicals produced by processing the meat and from cooking.

FILE: The decision to stop eating meat is a personal choice. Picture: freeimages.com.

JOHANNESBURG - Last

week the World Health Organisation's (WHO) cancer arm, the International Agency

for Research on Cancer (IARC), announced that the consumption of processed andred meat is associated with an increased risk for colorectal cancer.

Professor

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?

The

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

lifestyle factors.

Close to

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.

The

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.

Once the

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

to humans.

To date,

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

The IARC

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).

A

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.

A

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.

The

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?

The risk

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?

The

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.

Consumers

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.

The top

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

The

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.

Colorectal

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.

Prostate

cancer is most common in the Caucasian population, whilst colorectal cancer is

high among the Caucasian and Asian populations.

Reducing

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.