Red Meat, Processed Meat and Cancer
An explanation of the IARC report about red meat, processed meat and cancer
What is the IARC and what do they do?
IARC is the International Agency for Research on Cancer and it is an agency of the World Health Organization, (WHO) that looks at substances and other environmental factors which pose a risk of cancer in humans, e.g., chemicals, lifestyle factors. They do this by asking a panel of experts to evaluate the balance of evidence in the scientific data concerning a particular environmental factor and the risk of cancer. On the 26th October 2015, they published the results of their evaluation of the risk of developing cancer from the consumption of red meat and processed meat.
What is red meat?
The IARC report refers to red meat as all mammalian muscle meat, including, beef, veal, pork, lamb, mutton, horse, and goat. It does not include poultry and fish.
What is processed meat?
The IARC report refers to processed meat as meat that has been transformed through salting, curing, fermentation, smoking, or other processes to enhance flavour or improve preservation, e.g., hot dogs (frankfurters), ham, sausages, bacon, and salami.
What is a carcinogen?
A carcinogen is a substance that has been associated with cancer in humans.
What does the IARC classification system for carcinogens mean?
IARC classifies carcinogens into five categories as follows:
Carcinogenic to humans
Probably carcinogenic to humans
Possibly carcinogenic to humans
Not classifiable as to its carcinogenicity to human
Probably not carcinogenic to humans
It is important to understand that this classification system indicates the weight of the evidence as to whether an agent is capable of causing cancer. It does not measure the likelihood that cancer will occur as a result of exposure (i.e. the level of risk) so it is not an indication of how potent the agent is as a carcinogen.
Red meat was classified as Group 2A “probably carcinogenic to humans”. What does this mean exactly?
In the case of red meat, the classification is based on limited evidence from epidemiological studies (studies involving observations of cancer rates in different groups of people eating different diets) showing positive associations between eating red meat and developing colorectal cancer as well as strong mechanistic evidence (reasons for how red meat might cause cancer)
Processed meat was classified as Group 1, “carcinogenic to humans”. What does this mean?
This category is used when there is sufficient evidence of carcinogenicity in humans. In other words, there is convincing evidence that the agent causes cancer. The evaluation is usually based on epidemiological studies showing the development of cancer in exposed humans.
What types of cancer is linked to red meat consumption and how could it happen?
The strongest, but still limited, evidence for an association with eating red meat is for colorectal cancer. This is cancer of the colon and/or rectum which are both parts of the bowel.
There are compounds in red meat like haemoglobin that can trigger production of N-nitroso compounds during digestion and these chemicals can be carcinogenic. Also cooking red meat at high temperature (grilling, frying, roasting, barbequing) can also lead to the formation of chemicals that can be carcinogenic, e.g., polycyclic aromatic hydrocarbons.
Should I cook my red meat less?
It is important to cook red meat thoroughly to an internal temperature of at least 75 oC to kill harmful bacteria. The exceptions to this are whole, untenderised cuts of beef or lamb, e.g., steaks, which can be cooked to preference. However, the less browned or burned the outside of the meat is, the fewer carcinogenic chemicals are formed.
What types of cancer is linked to processed meat consumption?
IARC concluded that eating processed meat causes colorectal cancer. An association with stomach cancer was also seen, but the evidence is not conclusive. The consumption of processed meat was associated with small increases in the risk of cancer in the studies reviewed.
There are similar compounds in processed meats as red meats that may cause cancer (see Q. What types of cancer is linked to red meat consumption and how could it happen?) processed meats may also contain other chemicals as a result of their processing/preservation that may be associated with cancer, e.g., nitrites in cured meats.
Is there any cancer risk associated with poultry or fish intakes?
No, there is no cancer risk associated with poultry or fish intake. Poultry has much lower amounts of haemoglobin and does not trigger the production of N-nitroso compounds in the body. This may explain the lack of cancer association with poultry intake.
In many studies, fish intake appears to be protective against cancer. This may be due to some extent to the protective effects of fish oils; however some protective effects have been seen in white fish.
Should I avoid red meat altogether?
No. Lean red meat1 consumed in moderation can be a valuable part of a healthy diet as it is a good source of protein and a particularly good source of absorbable iron.
However consumers should avoid consuming large quantities of red meat, especially processed meat (high in fat and salt).
1Lean beef, pork, lamb the size and thickness of the palm of your hand (without fingers and thumb) shows how much meat, poultry or fish you need in a day. Most of this can be used for your main meal, with the remainder (if you want) used for your light meal.
What is moderation?
Healthy eating is all about ‘moderation’ which means avoiding large portion-sizes and frequent consumption (i.e. be careful on how much red meat you eat at any one time and how often you eat it). The amount of red meat you need in a day relates to your body size and an easy way to estimate this is to choose a portion that is the same size as the palm of your hand without your fingers and thumb. On average this is approximately 100g (4oz).
Choose alternatives to meat – such as fish (protective against colon cancer), poultry (no effect on colon cancer or beans/lentils (vegetarian protein foods that provide fibre that protects against colon cancer) so that you only choose red meat as a main meal three days a week. This keeps red meat intake to 300g per week, which is an amount previous reports have indicated is best.
For more detailed information on the best food choices see Healthy eating, food safety and food legislation.
What should I eat to prevent cancer?
Cancer is a complex disease and can be caused by a number of factors including genetics, smoking and other environmental factors. However, healthy eating can play an important role in the prevention of cancer. Here is some of the best advice for healthy living to prevent cancer:
- Be a healthy weight
- Be active
- Avoid alcohol
- Eat plenty of fruit & vegetables
- Choose different types of fruit and vegetables
- Choose wholegrain breads and cereals
- Avoid excess fats and oils