If you watched the news, read newspapers or surfed the web recently you will have been inundated with pictures of bacon and headlines describing it as carcinogenic. That鈥檚 because the International Agency for Research on Cancer (IARC) classified processed meats as being carcinogenic, placing them in the same category as tobacco smoke, asbestos, oral contraceptives, alcohol, sunshine, X-rays, polluted air, and inhaled sand. However, it is critical to understand that the classification is based on hazard as opposed to risk. Hazard can be defined as a potential source of harm or adverse health effect. Risk is the likelihood that exposure to a hazard causes harm or some adverse effect. If a substance is placed in IARC鈥檚 Group 1, it means that there is strong evidence that the substance can cause cancer, but it says nothing about how likely it is to do so. That likelihood depends on several factors including innate carcinogenicity, extent of exposure and personal liability. Ultraviolet light, a component of sunlight, is a good example to illustrate the difference between hazard and risk
Light can be thought of as being composed of packets of energy called photons. When a photon impacts a molecule of DNA it can damage it, triggering an irregular multiplication of cells, in other words, cancer. X-rays are also made up of photons, but these are more energetic than the photons of ultraviolet light so they are more likely to damage DNA. Although both sunlight and X-rays are in Group 1, X-rays are clearly more capable of triggering cancer than sunlight. But exposure matters. A single chest X-ray is not a problem but repeated baking in the sun is. More photons of lower energy can have a greater effect than fewer photons of greater energy. Then there is individual liability. A person with dark skin is less at risk for developing cancer than someone with pale skin even at the same ultraviolet light exposure.
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Inhaled sand is also listed in Group 1. That鈥檚 because studies have shown that workers engaged in occupations that can result in inhaling sand show a significantly increased risk of cancer. But this doesn鈥檛 mean that going to the beach and frolicking in the sand is a risky business. Tobacco smoke is also in Group 1because there is no doubt that it causes lung cancer. In fact about ninety percent of all lung cancer cases can be attributed to smoking. Alcohol is also in this category because it is known to increase the risk of oral cancers as well as breast cancer, yet nobody worries about drinking a glass of wine. Listing processed meat in IARC鈥檚 Group 1 just says that like alcohol, like tobacco, like sunshine, and some 180 other chemicals, mixtures and exposure circumstances, it is capable of causing cancer. It does not mean that if you have a bacon lettuce and tomato sandwich you are putting yourself at risk.
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Let鈥檚 clarify what is meant by processed meat. Grinding meat into hamburger does not result in processed meat. But smoking, fermenting or adding chemicals such as salt or nitrites to either extend the product鈥檚 shelf life or change its taste does. We鈥檙e talking about bacon, sausages, hot dogs, salami, corned beef, beef jerky and ham as well as canned meat and often meat-based sauces.
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The evidence that these tasty morsels are linked to cancer comes from observational studies, which of course do not prove cause and effect. But they are quite consistent in demonstrating that populations that consume lots of processed meats have higher cancer rates, particularly colorectal cancer, even when corrections are made for smoking, other foods eaten and activity levels. Furthermore, there are theoretical and experimental foundations for declaring some components found in processed meat, like polycyclic aromatics, heterocyclic amines, nitrites, insulin-like growth factor and heme-iron, carcinogenic.
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The evidence is certainly not ironclad, but science rarely is. It comes down to making educated guesses and evaluating the downside of such guesses. There is no significant downside to limiting processed meat, especially if it is replaced by plant products. But the significant question to ask is how much can we reduce our risk of colorectal cancer by robbing our taste buds of the taste of bacon and such? The risk of this cancer in the general population is roughly six in a hundred. After poring through some 800 peer-reviewed publications, IARC estimates that eating 50 grams of processed meat every day over a lifetime increases risk by about 18%. In other words, if a hundred people follow such a regimen over a lifetime, there will be seven cases of colorectal cancer instead of six. So for an individual, the chance of getting colon cancer because of eating processed meats is about 1 in 100. That is a very small risk, but because there may well be millions of people following such a diet, the impact on the population can be significant, in IARC鈥檚 estimate, about 34,000 cases a year.
What do we do with this information? A one in a hundred chance is not insignificant and it makes sense to try to reduce it. That means consuming less than 50 grams of processed meat a day on average. To do that we need to keep some numbers in mind. Two to three strips of bacon add up to 50 grams, as do two slices of ham, 4 slices of salami or one hot dog. Remember though that we are talking averages here. Certainly a couple of hot dogs, a salami sandwich and a couple of bacon and egg breakfasts a week is not a great risk. But if you have a smoked meat sandwich, well, you have used up your weekly allotment. But remember that all these numbers are estimates, basically educated guesses, and are not based on hard evidence.
