Red meat kills? It’s flagrant bias that’s killing me…

This week the media has been awash with news about the perilous dangers of eating red meat, and processed meat in particular. The cause of this consternation was a study published in the Archives of Internal Medicine which analysed data from two large ‘epidemiological’ studies [1]. These studies basically followed people over many years monitoring (infrequently) their diets and lifestyle habits and seeing if there was any association between these and risk of things like heart disease, cancer and overall risk of death.

An additional serving (82 g/3 oz) of unprocessed red meat was associated with a 13 per cent increased risk of death. Although it should be pointed out that many potentially processed forms of red meat were allowed into the ‘unprocessed’ category, including shop-bought hamburgers and meats used in sandwiches (this includes burgers, again).

An additional serving of processed red meat (e.g. two rashers of bacon or one hot dog) each day was associated with a 20 per cent increased risk of death.

Now, one major problem with this sort of evidence is what is termed ‘confounding’. Just because two things (e.g. red meat and death) are associated, does not mean one is causing the other. Sometimes, such an association can be down to what are called ‘confounding factors’: other associated factors that are the real cause of the association. For example, people who eat more red and processed meat might also smoke more. Or perhaps they are more likely to be obese and sedentary.

As it happens, in the populations used in this recent study, those who ate more red meat were less likely to be physically active, more likely to smoke and drink alcohol, and were generally heavier too. In other words, those eating more red meat were generally less healthy and, seemingly, less health-conscious.

Of course, this is exactly what you’d expect, because for decades now we’ve been warned of the dangers of red meat. So, individuals who have made a concerted effort to limit red meat in the diet are going to tend to be more health-conscious and healthier as a result.

In this week’s study, the authors have attempted to ‘control’ (take account for) for confounding factors. However, it’s well known that this is an imprecise science, and there’s always the potential for ‘residual confounding’ (confounding factors that were not addressed or not adequately controlled for). Interestingly, the authors of the study do not even mention the possibility of residual confounding, which seems like quite an omission to me.

This omission does smack a bit of bias, I think. Might the authors have been committed (even unconsciously) to finding a link between red meat and worse health outcomes, and were perhaps disinclined to let anything get in the way of that finding and the message that we should be eating less meat? Is there any other evidence for bias in this review? I believe there is.

In the ‘comment’ section of the review the authors refer to “Several studies [that] have suggested that vegetarians have greater longevity compared to nonvegetarians”, though they admit this might not be ascribed to the absence of red meat alone.

But is it true that vegetarians live longer than nonvegetarians? The studies which the authors refer to both date from 1999. One was a review of evidence in Seventh-day Adventists [2], while the other is an analysis of 5 separate studies [3]. There is considerable doubt about how appropriate it is to general the findings of Seventh-day Adventists to the general population, on the basis that their lifestyle habits tend to be quite different from the general population (e.g. low rates of smoking, low intakes of meat and alcohol).

This evidence also highlights the fact that any health issues associated with meat eating may not come from the meat per se, but a relative absence of other healthier foods. For example, in this study [2], vegetarians generally ate more vegetables, fruits and nuts. In fact, this study found evidence that the apparent health benefits of vegetarianism were tied not so much to the absence of meat, but to an increased consumption of perhaps healthier foods.

The other review [3] cited by the authors of this week’s study was interesting in that of the five studies analysed, two were performed in Seventh-day Adventists. Both found vegetarians to be at lower risk of death compared to non-vegetarians (see caveat above). However, the other three studies did not. And, actually, when all the results were put together, vegetarianism did not confer any benefit in terms of overall risk of death. In other words, the overall result of this review runs counter to the contention that vegetarianism is linked with improved longevity.

Another more recent study which compared mortality in vegetarians and nonvegetarians found, again, no difference in mortality between these groups [4].

In referring to evidence regarding vegetarianism, the authors of this week’s review appear to have been extremely selective and actually cited evidence which does not support their view. This smacks of bias.

This review is accompanied by an invited commentary from Dr Dean Ornish – a proponent of low-fat eating and a noted vegetarian [5]. He concludes, in a word, that the answer to the question of whether red meat is bad for us is ‘yes’. But he can’t possibly do that on the basis of this type of evidence. Nowhere in his commentary does he refer to fact that associations do not prove causality – it’s simply not mentioned.

Dr Ornish does refer, however, to human studies in which relatively high-protein, low-carbohydrate diets have led to improvements in health markers such as weight, blood pressure and blood fat levels. In fact these human studies (and there are many) have been found to improve a range of health markers across the board. But Dr Ornish dismisses these studies by referring to one single study which was, wait for it, performed in mice bred to have a genetic glitch which makes them particularly susceptible to heart disease. How this applies to humans is anyone’s guess, and one thing we know for sure it’s not relevance to humans is tiny compared to studies done in actual, err, humans.

Dr Ornish sweeps aside ton of good evidence is swept aside in favour of a small amount of quite useless science instead. More bias? You decide.

References:

1. Pan Am ,et al. Red Meat Consumption and Mortality: Results From 2 Prospective Cohort Studies. Arch Int Med epub 12th March 2012

2. Fraser GE. Associations between diet and cancer, ischemic heart disease, and all-cause mortality in non-Hispanic white California Seventh-day Adventists. Am J Clin Nutr. 1999;70(3)(suppl):532S-538S.

3. KeyTJ, et al. Mortality in vegetarians and nonvegetarians: detailed findings from a collaborative analysis of 5 prospective studies. Am J Clin Nutr. 1999;70(3)(suppl):516S-524S.

4. Key TJ, et al. Mortality in British vegetarians: results from the European Prospective
Investigation into Cancer and Nutrition (EPIC-Oxford). Am J Clin Nutr. 2009;89(5):1613S-1619S.

5. Ornish D, et al. What’s good for you is good for out planet. Arch Int Med epub 12th March 2012

24 Responses to Red meat kills? It’s flagrant bias that’s killing me…

  1. HighlySkeptical 15 March 2012 at 9:12 pm #

    Ty, for this Dr. B. However, bad studies like this are easily refuted. The Big Dog is coming our way right now in the form of Marion Nestle’s huge defense of conventional wisdom in her new book. Her work was just yesterday given near-rapturous applause in Nature. Once Nestle’s new book hits the mainstream, the insulin hypothesis will be basically finished. What we need is a similar critique of Nestle, but no one seems up to the task. Nestle is a nutrition player on the global level who advises governments, public agencies, and health authorities. I really think we need an answer to her, and relatively quickly, if we’re not to lose ground.

  2. Mike 15 March 2012 at 9:59 pm #

    The funny thing is, and Zoe Harcombe pointed this out, the raw data suggested that the death rate decreased from low meat eating to the quintile with the second highest amount of meat eating, yet when they ‘accounted’ for the risk factors of smoking, alcohol, and BMI (which all increased from quintile 1 to 5) and exercises (which decreased from quintile 1 to 5), the death rate changed from going down between quintile 1 to 4 to going up. One would think that eliminated increased risk factors should lower the death rates, not increase them.

    http://www.zoeharcombe.com/2012/03/red-meat-mortality-the-usual-bad-science/

    This strikes me as the way they ‘accounted’ for the risk factors was to use calculations that would favour the hypothesis that red meat was dangerous. You can’t have increased meat consumption for the first 4 sets of subjects causing a lower death rate, can you?

  3. tess 15 March 2012 at 11:53 pm #

    you found yet another wrinkle in this ridiculous “news story” that other reviewers haven’t — thanks! :-)

    …why do you suppose Harvard supports such bad science? are they getting a lot of money from Big Ag?

  4. Ben 16 March 2012 at 3:39 pm #

    An excellent critique!!! So many nutrition studies are flawed by not only by bias, but by looking at things the wrong way and asking the wrong questions.

  5. Tash Goswami 16 March 2012 at 3:45 pm #

    What crossed my mind was whether or not they took into account the non food elements added to meat esp. processed foods. Preservatives, sugars, hormones, added fats, bulking agents etc – what do these additives do to the human body long term?

    I would also query who exactly benefits from the study, who paid for it etc. I have a strong feeling that this will have also impacted on the outcomes. Also unless a subject is in a totally controlled enviroment ie not exposed to chemical additives in cereals, other processed foods, other polluntants in the atmosphere and given good healthcare etc then the study is intrinsically flawed.

    Eating excessive amounts of processed, ready cooked and meat based foods will have an adverse effect on anyone. Its a bit like putting a bit of petrol in a diesel car and expecting it run ok.

  6. happylikesquirrel 16 March 2012 at 3:49 pm #

    I had a look at the paper and they don’t seem to have recorded consumption of sugary or other simple carb foods, and we might well expect consumption of these to be higher amongst the red meat eaters who, as you say, might generally have less healthy habits. Seems like a major omission to me. Scary that this research was so poorly reported and so widely picked up.

  7. Cathy 16 March 2012 at 4:50 pm #

    The authors of the study have defined “meat” only in terms of processed or unprocessed. Since processed meat often contain additives such nitrates and sugars, I think we would be wise to limit its consumption since some of these ingredients may play a part in the chronic over- production of insulin and the ensuing damage that may cause – a possible common factor in current epidemics of obesity, diabetes, heart disease, cancers and dementia. Unprocessed meat requires further definition : would that be meat from grain fed or grass fed animals? I understand most US meat sources are from grain fed animals. Hormone supplementation in animal husbandry may be another factor to take into consideration. Wild or semi-wild sources such as venison are reputed to carry more Omega-3 fats and less Omega-6 which would surely reduce the inflammatory process underlying many degenerative diseases. The meat we eat today may be very different from that eaten even five or six decades ago and would certainly be different from that eaten by our distant ancestors. It’s puzzling that the study did not attempt to define their understanding of “meat” in terms of its source.

  8. Mike Rawlinson 16 March 2012 at 5:36 pm #

    This is an American study. American cattle are packed into high desity coralls where they never see a blade of grasss where they are fed on growth hormones, antibiotics , and genetically modified grain, soya beans, and a whole lot more that isn’t fit for any animal to eat, so it wouldn’t be surprising if the resulting meat is not good for anyone to eat.

  9. Karen 16 March 2012 at 8:34 pm #

    Good article! Here is another good one on the same study.

    http://www.marksdailyapple.com/will-eating-red-meat-kill-you/

    I liked these 2 sections in particular.

    “Ah, yes: here we see the folks eating the least red meat have the highest rates of elevated cholesterol, while the red-meat-indulgers have the lowest rates. Given the media’s eagerness to assign cause and effect to this study, it’s mighty strange none of the headlines proclaimed “Red meat reduces cholesterol!””

    “In case you’re skeptical that observational studies can run disturbingly contrary to reality, look no further than the hormone replacement therapy (HRT) craze that peaked a few decades ago. By 1991, 30 observational studies—including this one based on none other than the Nurses’ Health data—collectively showed that women taking estrogen seemed to have a 44% reduction in heart disease risk compared to their non-hormone-replacing counterparts. Naturally, this led literally millions of women to jump on the estrogen bandwagon in pursuit of better health and longer lives. A very unfortunate oopsie-daisy sprouted up later when some randomized, controlled trials finally emerged and revealed that rather than being protective, hormone replacement therapy actually increased heart disease risk by 29%!”

  10. Judy Barnes Baker 16 March 2012 at 8:58 pm #

    Another huge problem with this study is that it is based on food questionnaires filled out from memory. I was a contributor for a major data-collecting company in the US for a while. They basically told me to make up data if I didn’t really remember it or if the none of the multiple choice answers fit. You can read about my experience and why I quit here: http://carbwars.blogspot.com/2012/03/red-meat-will-kill-you-again.html

    Another thought about the study you mentioned of the 7th Day Adventists. A similar study of Mormons had the same outcome and Mormons eat meat. I suspect that the real advantage that both these groups have, as well as the Amish and other close-knit religious societies, is the stress reduction that comes from living in a group where everyone believes the same thing and follows the same rules.

  11. kate 16 March 2012 at 11:06 pm #

    The consequences of a diet in which red meat is consumed regularly? Shocking that anyone even studies this! (Does make you think… SHOULD make you think…) It’s your health. Gamble away. Long term, will cutting down on red meat and eating more whole foods in the form of fresh fruits and vegetables harm me? Hmmm. All those carbs.

  12. DanC 17 March 2012 at 12:25 am #

    All medical studies are flawed because any trial cannot be repeated to obtain the same results — the scientific method. The reason for this is that the study parameters cannot be standardized (“confounding factors” Dr B calls them) because all of the test subjects are different — they are human. Therefore, meta-analyses border on the fraudulent because the errors of the underlying studies are amplified and the results manipulated to produce the outcome the principal investigators desire.
    btw, Dr Ornish is a slick-talking quack used to raise funds for the Public Broadcasting System (PBS) in the U.S.

  13. Julie Regan 17 March 2012 at 1:47 am #

    So pleased that you highlighted what a load of c**p this news item was. Such confusing messages yet again from the people ‘in the know’.

  14. Megan 17 March 2012 at 2:16 am #

    I think this is little more than an attempt to pretend that red meat – which is becoming prohibitively expensive for ordinary incomes – is bad for us, anyway. There is increasing emphasis on the role of so-called healthy carbs as the basis of our recession diet. Let’s not forget that anything adopted with enthusiasm by our government from denatured low fat foods to statins is a disaster for the nation’s health. As for nitrates in processed meats, celery has plenty of naturally occuring same.

  15. Carole McIntosh 17 March 2012 at 6:23 am #

    I noted that they meant processed meats like Salami etc.
    It is the chemicals used in this process that is the problem
    But of course vegetarian people hit on the word meat and off they go

  16. Neal Matheson 17 March 2012 at 9:39 am #

    There’s no need to “hide”behind the processed meat angle. The study was complete bunk from top to bottom what the lowest quintile of women ate 1200 calories a day? The highest quintile of Red meat eaters had three times the amount of smokers. Oh the researchers adjusted for that did they? By what magical means did they do this?
    You won’t be able to convince anyone who is a vegetarian or a vegan or any one who actually believes through some kind of reverse darwinism that meat is actually bad for you. The newspapers said it, scientists from Harvard said it.
    The anti meat (let’s face it vegans) group won the PR war long ago. Meat gets defended by the “stuff and nonsense” brigade and foodies, thank God for Doctor Briffa (and others) and actual Doctor saying not only that meat isn’t bad for you but is actually quite good for you.
    I wouldn’t care at all if it weren’t for the spectre of legislation or satfat taxes.

  17. Chris Hilder 17 March 2012 at 4:10 pm #

    Thanks Dr B for this important contribution and for your piece in the Saturday Times Weekend today. For a moment there I thought we had gone mainstream. Excitement dropped when I read HighlySkeptical’s comment above. At least they will not be able to stop me and my family eating correctly (by which I mean Low-Carb).

    The battle for health of our nation(s) the associated cost savings to the NHS and the benefits to the economy make the fight for the truth a political imperative I believe. Only the politicians with the support of the media have the ability to shame those who perpetuate the experiment of high carb diets which is so harming our society.

  18. Tom Coldwell 18 March 2012 at 12:39 am #

    As I see this analysis, those people with a raised tendancy to CHD are pre disposed to eating a greater than average amount of red meat. Those who do are likely to almost completely negate the problem. This indicates that for the average person eating red meat is a worthwhile strategy.

  19. Cathy 19 March 2012 at 4:34 pm #

    “It’s meat, Jim, but not as we know it.” I’m not surprised the researchers have found some adverse correlation between meat eating and health. Even if their methods are flawed, they have shot themselves or “big AG” in the foot by concluding the products of the meat industry may be harmful to health. There’s a world of difference between meat from a grass eating, organically reared animal and a mound of slurry from mechanically recovered parts of an animal raised in pharmaceutical hell which may still be legally described as “meat”.

  20. Tom 19 March 2012 at 4:52 pm #

    Ah good, they’re rolling out Ornish again. Dr. Dean “vegetarianism is what improves patient health, not the exercise, smoking cessation and stress management programme that accompanies my dietary changes” Ornish.

    I think a really important message regarding sustainability was raised by Mark Sisson recently; that is, if eating more meat and less grain is bad for the planet, fine (please note: I’m not convinced this is true). But it is an entirely separate issue to what is good for us to eat. If the government or farming bodies want us to eat nutritient-sparse sugar fodder for the sake of the planet, that certainly is an ethical decision to be weighed up. But whether or not it is optimal for us is a totally different question. Which then raises the interesting question: should we all eat inferior “chow” that potentially makes us sick, so that there’s food to go round?

  21. Malcolm 21 March 2012 at 2:09 am #

    It is also important to note that the article in question (and many others that have similar findings that result in a bad image for red meat) have yet to site any biochemical evidence for the toxic agent(s) in ‘red meat’. While the toxicity of excess carbohydrates, especially sugars, are well documented in humans there is no such evidence for a toxic agent(s) found in red meat. Any attempt to show causation must be supported by biochemical evidence on the mysterious and elusive toxic agent(s). We are pretty sure that fat isn’t the enemy. I wonder what they will come up with, or even whether they will bother to investigate the matter further, as it appears health advice doesn’t require good science, merely dogma. Surely they would wish to identify this toxic agent(s) so that we could all be more convinced of the their data? Maybe then we could even remove it from the meat so we could all eat as much as we’d like? Or maybe it’s not the meat at all. Keep fighting the good fight Dr. Briffa.

  22. Bernard 21 March 2012 at 1:32 pm #

    As a few suggest, don’t these mainstream (dillusional) idiots consider the source of the beef.

  23. Ron 29 March 2012 at 7:28 am #

    I don’t know if Ornish is personally a vegetarian, but he allows for animal products in his dietary recommendations:
    http://www.ornishspectrum.com/wp-content/uploads/food_pyramid.jpg

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