I love bacon

Blogging on Peer-Reviewed ResearchA reader, who happens to write one of the best-named blogs on teh tubes, pointed me toward an article I never would have seen. This parallels a news story we had here in the States late last year. So, since the story is getting press overseas (albeit late), it’s time to dust off the old post and update it a bit.

The story repeats the finding that processed meats increase the risk of colon cancer. This news comes from a large report published by the World Cancer Research Fund, which looks at data surrounding diet and cancer. It states that there is no safe level of processed meat consumption when it comes to colorectal cancer risk. It’s going to take a long time to parse through all the data, but since I love my processed meat, I’ll start there, and once again, my scientist colleagues will please forgive me for oversimplifying.

First, this is a huge report, pooling tons of data. One of the most important conclusions is regarding obesity and cancer risk, but that will have to wait until later.

Per USAToday, “every 1.7 ounces of processed meat consumed a day increases the risk of colorectal cancer by 21%.” Per the Daily Mail, “[e]ating just one sausage a day raises your cancer risk by 20 per cent.” What does that mean? “Risk” is a complicated concept in medicine. It is easy to draw overbroad conclusions from bits of data. When risk is measured, it is rarely intuitive–small percentages can indicate large increases in risk, large numbers can refer to small increases in risk–it depends quite a bit on the base line incidence and prevalence of the disease. A 50% increase in a disease sounds big, but in the right situation it can be big or small. For example, if your “usual” risk of disease A is 2/100, then a 50% increase makes your risk 4 in 100, meaning out of 100 people, 2 more get the disease then they would without the extra risk. If the “usual” risk is 10/100, then a 50% increase means 5 more people get the disease.

I hope you haven’t given up on me here. Keep reading…trust me…


Now, for a disease whose risk is 4/10,000, a 50% increase in risk means that 6/10,000 will get the disease–that’s not so many.

Let’s keep doing that math:

There are about 150,000 new cases of colorectal cancer in the U.S. every year, making the yearly “risk” of colon cancer about 1/2000. A 21% increase means that about 20,000 excess cases yearly, if everybody eats that yummy bacon, and if that risk increase can really be interpreted as applying to a yearly statistic. That’s actually quite a few people, so it’s worth looking at the data even more closely.

Referring to pages 122-123 in the report, about 16 studies were compared. (I pulled up the data from the Goldbohm study to look at a sample of what they were working with.) Many of the studies are small, and show minimal effects of processed meat on colon cancer incidence. The confidence intervals of most of the studies cross 1, meaning bacon may confer either risk or protection.

That being said, the data, in aggregate, show a possible trend in the direction of processed meat causing colon cancer.

So what does all this mean?

When the news anchor says that the risk of colon cancer is 21% higher with sausage, it does not mean your personal risk of cancer goes up 21%. These data show a trend toward increasing colorectal cancer risk with increasing consumption of processed meat. That’s it. That’s the only conclusion. There’s no need to induce vomiting to purge today’s breakfast. It might be wise to cut back, however.

Post Script:

If Mark Chu-Carroll or any other mathematically-inclined reader wishes to correct my math, I certainly won’t be offended.

Comments

  1. #1 Brian Schmidt
    March 31, 2008

    “The confidence intervals of most of the studies cross 1, meaning it may be equally likely that bacon reduces the risk of cancer.”

    Don’t you want the second clause to read, “meaning it is less likely but possible that bacon reduces the risk of cancer”?

  2. #2 PalMD
    March 31, 2008

    Thanks…will correct it to reflect reality.

  3. #3 Ed S.
    March 31, 2008

    Off-topic, but see: FDAConcerns.com. Reynolds says FDA should not have tobacco added to its workload, ’cause it’s already messed up. TV ads for the site are playing on Fox.

  4. #4 Ahcuah
    March 31, 2008

    There’s another confounding factor: if your genetics are such that processing the nitrates (or whatever) doesn’t lead to any higher risk at all, it could be that you in particular are not effected by the study at all. But for those whose genetics don’t process the nitrates well, your risk might be double of what they are quoting.

    And at this point, you don’t know which bucket you fall into.

  5. #5 Julie Stahlhut
    March 31, 2008

    Avoiding daily consumption of highly processed, high-fat, high-salt meats is probably a good thing for many reasons. Then again, they’ll take my Genoa salami away from me when they pry my cold dead provolone off it.

  6. #6 Bill
    March 31, 2008

    Yeah, but what if you eat your bacon raw…

  7. #7 daedalus2u
    March 31, 2008

    The largest source of nitrate in the diet is green leafy vegetables like lettuce and spinach. They have a few tenths of a percent, a few thousand ppm.

    Nitrate is well absorbed and is concentrated ~10x from plasma into saliva where it can reach levels of a few mM/L. Commensal bacteria on the tongue reduce that nitrate to nitrite and saliva after a nitrate rich meal (100 grams of lettuce or so) can reach 2 mM/L nitrite. When that nitrite is swallowed, in the stomach the low pH and reducing conditions decompose the nitrite to nitric oxide, which has been measured to reach levels of ~80 ppm (by volume).

    There is considerable thought that it is the nitrate in vegetables that is the agent that makes them healthy to eat. There has been no study demonstrating any adverse effects of modest consumption of nitrate.

    It is thought that it is the heme in red meat that is one of the cancer promoting agents by promoting peroxidation. Nitric oxide blocks heme from coordinating with O2. I think adding nitrite to food is a good thing. Nitrate gets reduced to nitrite in your gut anyway by all your commensal bacteria there.

    Humans are net generators of nitrate (from nitric oxide synthase).

    I haven’t looked at the referenced study yet.

  8. #8 marcia
    March 31, 2008

    Aside from all the interesting stat stuff, how about doing what’s just plain old right.

    Don’t eat pork.

    Hogs are raised in warehouses and never see the light of day.

    They’re smart, abused, and the waste is unreal.

    http://www.rollingstone.com/politics/story/12840743/porks_dirty_secret_the_nations_top_hog_producer_is_also_one_of_americas_worst_polluters

  9. #9 PalMD
    March 31, 2008

    Which doesn’t really differ from any other meat industries. I understand your positions, but I love meat, and I am unlikely to curb my instincts.

  10. #10 Bob O'H
    April 1, 2008

    It sort-of makes me proud that a British paper becomes the by-word for insane reporting.

    The report is huge, so have the journalists just mined it to get the one result that looks large and scary?

    Oh, and I don’t know what idiot produced fig. 4.3.4 in the report, but this is basic – LABEL THE EFFING AXES. “Here’s a does response. But we’re not going to tell you what is measured on the y-axis (relative risk? OR? Murders per bad graph?), or what the scale is”.

  11. #11 Tom
    April 1, 2008

    “For example, if your “usual” risk of disease A is 2/100, then a 50% increase makes your risk 4 in 100, meaning out of 100 people, 2 more get the disease then they would without the extra risk”

    Wouldn’t a 50% increase rather increase it to 3 in 100, and a 100% increase be 4 in 100?

  12. #12 csrster
    April 1, 2008

    I don’t need no hi-falutin’ matemajiks. If it’s in the Mail, it’s lie.

  13. #13 Vagueofgodalming
    April 1, 2008

    Of course, there’s the Mail’s touching naivete that British sausages contain meat…

  14. #14 Rev. BigDumbChimp
    April 1, 2008

    I make my own bacon.

    You can cut out all of the nitrates that way if you are worried and it’s WAY better bacon.

  15. #15 Rev. BigDumbChimp
    April 1, 2008

    … and my own sausage

  16. #16 marcia
    April 1, 2008

    Which doesn’t really differ from any other meat industries. I understand your positions, but I love meat, and I am unlikely to curb my instincts.

    Actually, it does differ from some the other big meat industry. Cows do not live in crowded warehouses with no sunlight.

    And their diet? Far different from what they would consume in the wild. They are omnivores and opportunists, and will eat virtually every plant or animal available in the wild. Favored vegetation includes acorns, any fruits, seeds or nuts, mushrooms, roots, bark, and some grasses.

    Wildness gives the flesh a far higher nutritional content, including omega 3 numbers and a much lower fat content.

    If you can easily eat bacon after reading this short page,

    http://www.chooseveg.com/pigs.asp

    then I’ve got to hand it to you. It is your instinct to eat bacon, but I don’t think it’s a human instinct to eat bacon from a warehouse. I don’t mean to be confrontational at all, but I do know that you may change your view about pig farming if you visit one of these warehouses and spend some time learning about the natural history of the animal.

  17. #17 Bill
    April 1, 2008

    Marcia said, “Actually, it does differ from some the other big meat industry. Cows do not live in crowded warehouses with no sunlight.”

    Marcia, pigs are raised inside that way to protect them from the deadly UV rays from the sun. They don’t want them to get skin cancer.

  18. #18 Rev. BigDumbChimp
    April 1, 2008

    marcia. Hog farms are disgusting and eco-unfriendly yes. Some of that has changed. However we still have the safest food supply in the history of man and it’s getting better. Yes we have food scares but taken as a percentage of the food consumed it’s minuscule. However, the mass production of Hogs has had some detrimental effects on the the actual quality food. Hogs have been bred to be leaner, less tasty and pretty boring compared to all of the breeds that used to be raised.

    Go here. When I can I buy meat from the Heritage folks. They use breeds of animals that have been almost lost because of how the large hog farms have bred the animals to be leaner, less tasty and consistent across the board. The heritage breeds are more “natural” (I know it’s a lame term but I’m drawing a blank here). They have more flavor, marbling of fat etc.

    If you don’t eat meat, then you won’t likey care much, but if you do, trust me they are worth the difference (if you can fork out the extra cash).

  19. #19 PalMD
    April 1, 2008

    Our meat industry is broken. It is poorly regulated. It needs increased regulation.

    If you believe killing and eating animals is cruel (and it probably is), then you have to weigh the benefits. In my case, I’m not a fan of the mistreatment of animals, but really, if we’re going to kill and eat them, that’s not very nice either.

    I am able to live with the moral ambiguity of eating my fellow creatures.

  20. #20 marcia
    April 1, 2008

    Killing and eating is neither nice/not nice. It is how we evolved. It is perfectly natural and should not result in moral ambiguity.

    However, as you stated, deregulation has resulted in unnatural birth, growth, and death of these animals, especially pigs.

    You have a choice to eat bacon from farms where this process of growth follows a more natural process, similar to how a wild pig would live. The more we buy their product, the bigger they get.

    I’m a vegetarian. My husband is not. However, he does not eat pork. It’s not for religious reasons. We aren’t religious at all. He has just seen and knows what I know.

  21. #21 PalMD
    April 1, 2008

    I don’t disagree as such, but if you think the way we treat cows or chickens is any better, you are deceiving yourself.

    I still eat them all, but I do recognize the problem.

  22. #22 daedalus2u
    April 1, 2008

    The biggest problem I have with no one eating meat is that then farm animals would go extinct. In the wild, essentially no wild animal ever dies of old age. They die by being chased by a preditor, being killed and eaten.

  23. #23 Mike
    April 2, 2008

    I have a few comments:

    1. “However, as you stated, deregulation has resulted in unnatural birth, growth, and death of these animals, especially pigs.”
    The livestock industries have never been “deregulated.” They have never been regulated to start with. Therefore, I do not understand why you think that a reduction in regulation has resulted in more unnatural births, growth and death of these animals. Part of the problem is the large numbers of farms. Just to pick a small state with a small cattle population, Maryland has over 3000 cattle farms. I do not know the total number of farms in the US, but to effectively regulate and check compliance would be neither cheap nor easy. The USDA FSIS is supposed to hire inspectors to examine both live animals before slaughter and carcasses after death. Over 2000 of the live animal inspector positions are not filled due to a lack of DVM’s who were trained in large animal health. If livestock farms are to be regulated and inspected (preferably by a large animal DVM), then structural changes need to be made in academia to accommodate the increased demand for DVM’s.

    2″I don’t disagree as such, but if you think the way we treat cows or chickens is any better, you are deceiving yourself.”

    While there is really no difference in the ways that chickens and pigs are raised, there is a difference with cattle. Just about all beef cattle are raised in the open on pasture. Calves are weaned between 7 and 9 months of age and then transported to a feed lot or backgrounded on pasture for several more months. Most breeding stock for cattle are kept in the open on pasture, which is the exact opposite of most breeding stock for chicken or pigs.

  24. #24 Oldfart
    April 5, 2008

    I may be wrong here but consider the cost of building the fencing required to keep a large, intelligent, omnivorous, rooting animal outside in a large pen. Pigs are raised the way they are because they are the way they are. They are neither cows nor chickens.
    Chickens could be range raised, I suppose, but they are difficult to herd and local foxes, coyotes and raptors would just love you to raise them out in a pasture. Cows at pasture are not often dragged off by foxes, coyotes and raptors.
    Commercial raising of meat is all about control and consistency, just as in any other business. That being said, I have a personal belief that the genetic diversity of our food stocks is important, whether it be plant or animal. I cannot support that belief with any facts, not being a scientist, but I’m sure some of you can.

  25. #25 Bill
    April 5, 2008

    It’s not about taste, it’s about dollars. Farms have to raise animals as efficiently as possible because the ones that don’t can’t make it on the prices the market will bear.

    As long as the marketplace insists on low quality meat and cheap prices, that’s what you will continue to get. Hogs left to a large lot to roam around will be less efficient. The energy expended roaming is better utilized going to growth of the animal.

    It’s not morality, it’s economics.

  26. #27 revere
    April 6, 2008

    First, Tom is correct. A relative risk of 2 (2/100 to 4/100) is a 100% increase in risk, not a 50% increase. No big deal. Also no big deal, but as an aside, Ahcuah’s comment:

    There’s another confounding factor: if your genetics are such that processing the nitrates (or whatever) doesn’t lead to any higher risk at all, it could be that you in particular are not effected [sic] by the study at all. But for those whose genetics don’t process the nitrates well, your risk might be double of what they are quoting.

    is also not quite accurate since unless the genetic difference makes a person eat more or less processed meat, it is not a confounder. It may, however, be an effect modifier.

    The issue you are raising here, PalMD, is the difference between relative risk, risk difference and attributable risk. Only risk difference is itself a risk, since risk is a probability and as such is not ambiguous. This makes your point in another way: not everything which is called “risk” is a true risk, technically speaking.

  27. #28 PalMD
    April 6, 2008

    Thanks…i still haven’t had a chance to correct that math error. I appreciate your assistance.

    Risk is an oft-misunderstood concept in the media.

    AR/NNH is not calculated nearly enough (assuming it is possible from the type of numbers given). I think that NNT/NNH is a helpful stat for public consumption, when it’s available.

  28. #29 DebinOz
    July 20, 2009

    My mother thinks that bacon is a food group.

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