Dear Brian Palmer:
You missed the mark by a pretty wide margin in your article in Slate on 1/22/2014 titled “Cooking Up Cancer? It wouldn’t be crazy to give up grilled, smoked, or fried food.” And the headline is downright irresponsible. This sort of stuff can really damage livelihoods and even marital relationships. You should publish a retraction.
There are several fatal flaws in the article: (1) The research you cite is irrelevant, (2) smoked meat and grilled meat are not the same, (3) chemically, all smoke is not the same, (4) epidemiological studies of this sort are iffy and fraught with quicksand, and worst of all, (5) you seem determined to be sensational.
The research you cite is irrelevant
Your article hangs on three research papers to which you linked. One was published 49 years ago in the USSR. One was published 24 years ago in Hungary. The other was published two years ago in the People’s Republic of China.
The 1965 study from the USSR is about smoked fish and stomach cancer. I know you did not read it because it has not been translated, not that it would have any relevance to current understanding of cancer in the US.
The second paper from 1980 studied the very high rate of stomach cancer in people in Hungary who home-smoke meats, apparently with softwoods. It is well known that evergreens and other softwoods contain resins that can be hazardous. Almost all smoked meats in the US are flavored with smoke from hardwoods such as oak and hickory and are produced in USDA licensed plants.
The Chinese paper is focused on a gene thought to increase breast cancer rates in women. They asked 800 women of Han ethnicity who had been living in Sichuan for at least 20 years to fill out a questionnaire on their diets. 400 had breast cancer, 400 did not. The researchers concluded that women with a certain variation of the gene may have a higher cancer risk, and if they eat a lot of the smoked meats they may have a higher risk still. In Sichuan Province some of the most popular smoked meats are tea smoked duck, camphor smoked pork, and the local bacon, which has been shown in one study to be high in the pathogenic bacteria Lactobacillus and Staphylococcus. Of course the Chinese food supply is poorly regulated, a fact that has been widely reported (not that ours is adequately regulated either).
Warning the entire US population that grilling, smoking, or frying is risky based on these studies is specious, and thoughtless.
Smoked meat and grilled meat are different and not all smoke is the same
At issue is the possible presence of two known carcinogens, heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs).
The National Cancer Institute says “HCAs are formed when amino acids (the building blocks of proteins), sugars, and creatine (a substance found in muscle) react at high temperatures.” The longer they are exposed to high temperatures the more HCAs form. USDA says “Some studies suggest there may be a cancer risk related to eating food cooked by high-heat cooking techniques as grilling, frying, and broiling. Based on present research findings, eating moderate amounts of grilled meats like fish, meat, and poultry cooked — without charring — to a safe temperature does not pose a problem.” It explains that charring meat is a fine way to create HCAs. In other words bad grilling may be bad for your health! Charring your meat is not only unhealthy it is unappetizing and ruinous to your reputation. When it comes to grilling, the best tasting foods are cooked over low temps most of the way although, sadly, many backyard cooks have not learned this yet. The best grillmasters have learned that the best tasting foods are made when the majority of the cooking is not over open flame, with a 2-zone setup.
Now let’s look at PAHs. According to the EPA “PAHs are created when products like coal, oil, gas, and garbage are burned but the burning process is not complete.” That includes the incomplete combustion of charcoal, wood, and meat drippings. Smoke includes as many as 100 compounds in the form of microscopic solids including char, creosote, ash, as well as combustion gases that include carbon monoxide, carbon dioxide, nitrogen oxides, polymers, and liquids such as water vapor, and phenols. Complete combustion produces much less smoke, and PAHs, than smoldering, which is incomplete combustion. Smoked meat is usually made by incomplete combustion, at low temperatures so it is low in HCAs and high in PAHs.
Propane grilling is the most popular outdoor cooking method in the US and burning propane produces almost no smoke. While a charcoal fire is starting it can produce smoke, when it is fully lit it produces little smoke. Drippings from the food can produce smoke, but the contents of that smoke are a lot different than the smoke from a hardwood fire, a softwood fire, or a smoldering tea fire. Even so, grilling most meals goes so quickly that there isn’t enough time for smoke to accumulate in significant quantities on the meat. The amount of PAHs are small.
The three research papers were all about smoked meat which is different from grilled meat. There are, broadly speaking, two ways to smoke meat, cold smoking and hot smoking. The type of smoked meats in your three studies are usually made by a process called cold smoking. The food is not heated much. It is preserved by the smoke. Very few Americans have the equipment and expertise to cold smoke in their back yard. Cold smoking at home is in and of itself risky from a microbial standpoint and not recommended unless it is done precisely. One wonders how precisely it is being done in the back yards of Hungary and China. Cold smoking usually involves smoldering wood, higher in PAHs. Many smoked meats are also treated with a “curing” agent containing high concentrations of salt and preservatives. Almost all our cold smoked meats come from USDA licensed processors using hardwoods.
Hot smoking heats and cooks the meat. It is becoming popular in the US, as in Southern barbecued ribs or pulled pork, and Texas beef brisket. As pitmasters know, the smoke of a hot hardwood fire, called blue smoke, looks and tastes very different from a low smoldering fire. A good pitmaster seeks blue smoke, clean hardwood combustion which will contain fewer PAHs. And even duffers who produce white smoke don’t normally eat hot smoked meats as often as the softwood using subjects of the Hungarian study.
Epidemiological studies can be very iffy
Called epidemiological studies, population surveys are best used to suggest future experiments that directly measure the relevant variables. My associate, Prof. Greg Blonder, former head of research at Bell Labs, explained that “There are far too many uncontrolled variables in surveys, especially surveys that ask participants to recall past eating habits. There can also be social, economic, and genomic differences underlying smoked meat eating rates and these factors may point at the true root cause of slightly elevated cancer risks.”
An example: If you study people who watch a lot of TV you will discover they tend to be more overweight. You might easily conclude that there is something in the radiation from the screen that causes obesity and therefore televisions are unsafe. That’s the problem with initial epidemiological studies. Says Dr. Blonder “Only large scale population studies that directly measure, say the HCA content of food, can tease out cause and effect. And eliminate other plausible hypothesis.”
Could the curing agents in cold smoked meat be a factor more important than the smoke? Could breathing the foul air in China be a cumulative factor as women age? What about the pork in China? Could it be that the pork in China is often left to dry at room temperature? What about the softwoods? And how many of us eat smoked meat as often as Hungarians?
Dr. Blonder points out that “Many meat eaters do not eat their veggies, and thus miss the cancer protective value of greens. The smoked meats may not be causing cancer, but the lack of veggies are.” The same could be true in the recent studies saying that people who eat red meats have a higher risk of cancer (and let’s not get into the fact that they do not consider cooking methods, and that they included cured meats in the red meat category, but don’t get me started).
Tobacco is totally irrelevant
You go off on a baffling lengthy tangent discussing how we were slow to recognize the hazards of tobacco smoke, wondering aloud if we might be doing it again with grilled foods putting society at risk. Science and politics were very different in 1879 when you start tracing tobacco research and all through 1964 when the government unambiguously called smoking dangerous. The small quantities of smoke particles from hardwood that land on the surface of food are chemically altered by other ingredients and the cooking process. They are then ingested where they are again chemically altered. That is very very different from tobacco smoke that is inhaled in concentrated quantities across the tongue directly onto the lungs.
Dr. Blonder says that “The incidence of lung cancer in cigarette smokers is enormous. Smokers in a low pollution country have ten to twenty times the rate of lung cancer of non-smokers. These sobering numbers demanded legal restrictions against cigarette smoking. But the evidence is much weaker for avoiding smoked meat. Even the most alarmist, preliminary studies indicate a possible 20% increase in total cancer rates. Other than the word smoke, the risks have very little in common.”
And the mention of Nazi research on tobacco and Hitler’s opinions is incendiary and clearly demonstrates your desire to be sensational. This is an incredible red herring. Why not add gunsmoke to the discussion?
What we know
I have followed the “grilling causes cancer” story for years and as far as I can tell grilling, hot smoking, or properly made cold smoked meats from a USDA inspected plant have not yet been shown to be risky. Nobody has uncovered the, ahem, smoking gun yet. That said, smoke on the surface of food needs to be studied the like any food ingredient. I would be interested to see a study conducted by tracking the diets of competition barbecue cooks and judges, people who eat far more hot smoked foods than the general population. Who knows? We may discover ingredients in these foods that are good for us.
Here’s what I have learned: Everything in moderation. I have also learned, and any food safety expert will back me up, the riskiest foods are raw foods. Heat kills pathogens. Bambi, Thumper, Porky, and Tweety romping through the salad fields are what keep food safety experts up at night, not the grilled steak they had for dinner. And the riskiest food of all is raw bean sprouts.
Stating that “It wouldn’t be crazy to give up grilled, smoked, or fried food” is so far from true that you had to try to cover your ass by hedging: “None of these studies is definitive. It’s possible that other variables account for the correlations between cancer and cooking over a flame or at high heat, or that the carcinogenicity of PAHs observed in animal studies overstates the risk. But the risks are worth taking seriously.” No. They are not. There is no reason to eat less grilled or smoked foods unless you already consume them in excess. These studies and others I have seen show no risk to the US population.
Your article is the type of thing that scares consumers and serves to confuse not enlighten. For what reason? Because one Slate columnist wanted to start a fire and obscure the facts with smoke? Food and health is a vital topic. We need good lab research and intelligent writing on the subject. Especially from prestigious publications like Slate.