Eating meat and cancer
November 1, 2007
Lindsay McIntosh/The Scotsman/November 1, 2007
Bacon, smoked ham and processed sausages are a cancer threat and should be cut from people’s diet altogether, according to the world’s most comprehensive study of the disease.
The World Cancer Research Fund says the evidence is now strong enough for it to recommend that people stop eating all processed meats, whether they have been smoked, cured, salted or preserved with chemicals.
The report, which looks at thousands of scientific papers and has taken five years to compile, provides an exhaustive guide to trying to reduce your risks of getting cancer.
It reveals direct links between the disease and levels of obesity and alcohol consumption. It advises people to cut down on red meat, eat more vegetables and to do more exercise. It says mothers should also try to breastfeed for six months or longer.As well as lifestyle factors, which can be altered, the document says tall people are more likely to develop cancer of the bowel and breast.
The report was hailed by charities and nutritionists, who said it had succeeded in collating relevant information in one document. But the meat industry and some experts urged caution.
The report, Food, Nutrition, Physical Activity, and the Prevention of Cancer, says processed meats are a convincing cause of colorectal cancer and there is no level of intake that can “confidently” be shown not to raise the cancer risk. Processed meats are also thought to bring about an increased risk of cancers of the oesophagus, lung, stomach and prostate.
As well as bacon and ham, the report mentions pastrami, salami, sausages and hotdogs in its definition of processed meats. Sausages that have been treated with preservatives are included, although it is not clear whether those made only from fresh meat are.
The report says evidence that red meat causes bowel cancer is increasing and recommends people should have no more than 500 grams of cooked red meat a week.
The report also links obesity with six of the most common cancers. Previously, high body-mass has been found to be a likely cause of endometrial cancer – cancer of the womb lining – but the report extends this to take in oesophagus, pancreatic, bowel, post-menopausal breast and kidney cancers.
Professor Martin Wiseman, the project director, said: “This report is a real milestone in the fight against cancer. Its recommendations represent the most definitive advice on preventing cancer that has ever been available anywhere in the world.”
Sir Michael Marmot, professor of epidemiology and public health at University College London and the survey chairman, said there was a “very clear message” from the findings – don’t put on weight, do lose it if you already are overweight.
“We know that if you smoke, you increase your risk … but with obesity and being overweight, it is very clear and it is a graded phenomenon,” he said.
The report also reinforces previous findings that alcohol is linked with cancer, and the more you drink, the higher the risk.
But Prof Marmot said this had to be balanced with its ability to protect against heart disease.
Experts welcomed the report, with many saying that, although they were already aware of its findings, it was good to have them reported in one place.
Antonia Dean, a clinical nurse specialist for the Breast Cancer Care helpline, said it was important, however, that the causal findings in the report were kept in perspective.
She went on: “You can’t eliminate the risk [of cancer] and it is important people realise they can do everything on this list and still get cancer.”
Dr Sarah Cant, policy manager at Breakthrough Breast Cancer, said: “This report highlights what we’ve known for some time – that maintaining a healthy weight, taking regular exercise, breastfeeding for at least 12 months in total and limiting your alcohol intake can decrease your risk of developing breast cancer.”
Quality Meat Scotland, the representative body for the industry, insisted meat was safe as part of a balanced diet.
A spokeswoman said: “It is difficult to say what impact the report will have on the industry.
I think people have to follow independent advice, and that recognises that meat has a positive role when eaten as part of a balanced diet.”
Professor Ian Rowland, head of the Hugh Sinclair Unit of Human Nutrition at Reading University, said: “The main take-home message is that you should enjoy a balanced, healthy diet and not overeat. If you do that, the occasional rasher of bacon is unlikely to cause any harm.”
RECOMMENDATION: All meals should be based on plant foods. At least five portions of non-starchy vegetables and fruits should be eaten per day.
EVIDENCE: Fruit and non-starchy vegetables, including green leafy varieties, broccoli and aubergine, “probably” protect against cancers of the mouth, pharynx and larnyx, oesophagus and stomach. Fruit is also thought to protect against lung cancer.
Evidence of non-starchy vegetables’ abilities to protect against cancers of the nasopharynx, lung, colorectum, ovary and womb is limited.
The same is true of the ability of fruit to protect against cancers of the nasopharynx, pancreas, liver and colorectum.
Carrots offers “limited” protection against cervical cancer, while garlic “probably” helps to prevent bowel cancer.
The scientists say that as well as containing vitamins and minerals, which help to keep the body healthy and strengthen our immune systems, fruit and vegetables are a good source of substances such as phytochemicals, which can protect cells from cancer-causing damage.
RECOMMENDATION: Eat no more than 6g of salt (fifth of an ounce) or 2.4g of sodium a day.
EVIDENCE: Salt and salted food are “probable” causes of stomach cancer. It is also “probable” that Cantonese-style salted fish causes cancer of the nasopharynx.Most people in the UK currently have more salt than this.
There is also evidence in the report that refrigeration indirectly protects against some cancers because it increases the availability of fresh, perishable foods like vegetables and fruits, and reduces the need for processed foods, which are often high in salt, fat and sugar.
RECOMMENDATION: Cut out processed meat such as pastrami, bacon and certain kinds of ham from your diet altogether.
EVIDENCE: Researchers say there is convincing evidence that processed meat is a cause of bowel cancer. Most alarmingly, perhaps, they say there is no level of intake that can “confidently be shown” not to raise the cancer risk.Processed meat is also thought to bring about an increased risk of cancers of the oesophagus, lung, stomach and prostate.
And smoked foods – by which the researchers say they mean mainly meat – also increase the risk of stomach cancer.
Processed meat refers to any meat preserved by smoking, curing or salting, or by the addition of preservatives. Other examples include salami, as well as hot dogs and some sausages. When meat is preserved in those ways, cancer-causing substances can be formed.
Burgers and minced meats only count as processed meat if they have been preserved with salt and chemical additives.
RECOMMENDATION: People should aim to be towards the lower end of the healthy body mass index (BMI) range, which is 18.5 to 24.9 – calculated by dividing your weight in kilograms by the square of your height in metres.
EVIDENCE: Obesity is the key causal factor of cancer, with it being linked to a huge range of common forms of the disease. The report claims to have found a “convincing link” between body fatness and cancers of the oesophagus, pancreas, bowel, womb and kidney, as well as post-menopausal breast cancer.The report also suggests, conversely, that “fatness” probably protects women from pre-menopausal breast cancer.
Fat around the waist is a separate risk factor. Scientists say the evidence is “convincing” that girth there increases the colorectal cancer risk and probably also cancers of the pancreas and womb, and post-menopausal breast cancer.
RECOMMENDATION: Consumption of cooked red meat, like beef, pork and lamb, should be confined to less than 500 grams (just over 1lb) per week. The weight guidelines refer to the cooked meat.
EVIDENCE: The evidence that red meat causes bowel cancer has grown much stronger over the last decade.
Red meat contains substances that are linked to the cancer. For example, haem, the compound that gives red meat its colour, has been shown to damage the lining of the colon.
There is “limited evidence” that the food can increase the risk of lung cancer. Also, studies have shown that people who eat a lot of red meat tend to eat fewer plant-based foods, so they benefit less from their cancer-protective properties.
The evidence before the panel “was too limited in amount, consistency or quality to draw conclusions” about any links between poultry and cancer.
FINDING: Unusually, tall people may be at a higher risk of various cancers.
EVIDENCE:The evidence that greater height is related to cancer has increased since the 1990s.
There is an association between tallness and bowel and post-menopausal breast cancer.
For bowel and all breast cancers, the relative risk of developing either increased by 9 per cent for every extra two inches in height. There was also a “probable” link between being tall and pancreatic cancer, pre-menopausal breast cancer and ovarian cancer.
However, the scientists said tallness was unlikely to be a cause of cancer in itself. Rather, it acted as a “marker” for genetic, environmental, hormonal and nutritional factors affecting growth from the womb to early adulthood.
It was these factors that may have a bearing on cancer risk.
RECOMMENDATION: Try to ensure you are moderately active for 30 minutes a day and, as fitness improves, increase this to 60 minutes of moderate activity.
EVIDENCE: Physical activity in any form helps lower cancer risk, says the report, and evidence for the link has grown in recent years. It says it protects against colon cancer, probably post-menopausal breast cancer and womb cancer. There is limited evidence exercise protects against cancer of the pancreas, and lung cancer. It may strengthen immunity, help keep the digestive system healthy, and allow for the consumption of more cancer-protective nutrients.
RECOMMENDATION: Do not use vitamin and mineral supplements as a substitute for a balanced diet.
EXPLANATION: Eating a variety of foods is better. Foods are thought to contain anti-cancer substances which may not be possible to convert into pills or vitamins. Wholefoods rich in nutrients also contain substances like fibre.
RECOMMENDATION:Women should breastfeed exclusively for six months.
EVIDENCE: The researchers say they have discovered convincing evidence that breastfeeding protects both mother and child from cancer.
It says there is also convincing evidence that breastfeeding protects against pre-menopausal and post-menopausal breast cancer. There is also limited evidence that it protects against cancer of the ovary.
And there is evidence that being breastfed probably protects babies from becoming overweight or obese in later life.
Scientists think that breastfeeding lowers the levels of some cancer-related hormones in the mother’s body, which reduces the risk of breast cancer. At the end of breastfeeding, the body gets rid of any cells in the breast that may have DNA damage. This reduces the risk of breast cancer in the future.
If women are able to, they should aim to breastfeed their baby exclusively for six months, then continue with complementary breastfeeding after that.
RECOMMENDATION: Men who drink should limit themselves to two units a day, women to one (a small glass of wine contains a unit of alcohol).
EVIDENCE: The report cites “convincing evidence” that alcohol causes cancer of the mouth, pharynx and larynx, oesophagus, bowel cancer in men, and breast cancer. It also points to “probable evidence” that drinking is a cause of liver cancer and bowel cancer in women. However, it does recognise moderate amounts of alcohol may have a protective effect on the risk of coronary heart disease.