Processed meats are carcinogenic, says new review of evidence

Processed meats such as sausages, bacon, ham, and corned beef have been classified as carcinogenic by the cancer arm of the World Health Organization. They now appear in the same risk group for cancer (group 1) as asbestos, cigarettes, and alcohol.

WHO’s International Agency for Research on Cancer issued the new ranking after reviewing the evidence and finding that eating processed meats causes colorectal cancer, publishing its findings in a monograph and a summary in Lancet Oncology.1 2 It also found that processed meats were associated with stomach cancer.

The 22 experts who considered the evidence on behalf of the agency concluded that each 50 g portion of processed meat eaten daily increased the risk of colorectal cancer by 18%.

Non-processed red meat was classified as probably carcinogenic (group 2A), with limited evidence linking its consumption with colorectal cancer and strong evidence that the breakdown of meat in the body could lead to cancer. Red meat was also linked to pancreatic and prostate cancer.

Kurt Straif, head of the IARC Monographs Programme, said, “For an individual, the risk of developing colorectal cancer because of their consumption of processed meat remains small, but this risk increases with the amount of meat consumed. In view of the large number of people who consume processed meat, the global impact on cancer incidence is of public health importance.”

The new classifications match those of the World Cancer Research Fund International and fit with advice from experts on cancer, who have been saying for many years that a diet high in fibre, fruit, and vegetables and low in processed and red meat reduced the risk of cancer.

But many nutritionists were keen to point out the benefits of some red meat in the diet.

Elizabeth Lund, an independent consultant in nutritional and gastrointestinal health and former research leader at the Institute of Food Research, said, “Data from 2011 indicate the lifetime risk for bowel cancer in the UK is about 58 men per 100 000 and 38 women per 100 000. An increased risk associated with red meat consumption is in the region of 28%. A much bigger risk factor is obesity and lack of exercise. Overall I feel that eating meat once a day combined with plenty of fruit, vegetables, and cereal fibre, plus exercise and weight control, will allow for a low risk of colorectal cancer and a more balanced diet.”

Tom Sanders, professor emeritus of nutrition and dietetics at King’s College London, said that the International Agency for Research on Cancer’s rankings did not take into account the size of the risk from meat.

“Generally for colorectal cancer, where the data is more consistent than other sites of cancer, the relative risks [associated with red meat consumption] are small: 1.1 to 1.3. This is in contrast to the large variation in colorectal cancer between different countries,” he said. “Red meat is a good source of heme iron, which is better absorbed than plant sources. It is also a good source of zinc and vitamin B₁₂. Iron and zinc deficiency are major nutrient deficiencies of concern worldwide, but you do not need to eat large amounts of meat to get what you need—say, 30 g a day would be sufficient.

“The problem with this issue is that food is not like tobacco—we have to eat something.”

Ian Johnson, emeritus fellow at the Institute of Food Research, said, “It is certainly very inappropriate to suggest that any adverse effect of bacon and sausages on the risk of bowel cancer is comparable to the dangers of tobacco smoke, which is loaded with known chemical carcinogens and increases the risk of lung cancer in cigarette smokers by around 20-fold.”

The North American Meat Institute said that the agency’s new classifications defied common sense and numerous studies. Betsy Booren, the institute’s vice president of scientific affairs, said, “It was clear sitting in the IARC meeting that many of the panellists were aiming for a specific result despite old, weak, inconsistent, self reported intake data. They tortured the data to ensure a specific outcome.

“IARC says you can enjoy your yoga class, but don’t breathe air (class I carcinogen), sit near a sun filled window (class I), apply aloe vera (class 2B) if you get a sunburn, drink wine or coffee (class I and class 2B), or eat grilled food (class 2A). And if you are a hairdresser or do shift work (both class 2A) you should seek a new career.”