Why we can’t rely on epidemiological evidence

I came across this post recently, on the website of a Tom Naughton – a comedian and now nutritional commentator based in the US. Now I should imagine that comedians don’t necessarily make for the best nutritional commentators ordinarily. But Tom is an exception to this rule – he does a great job, in my opinion, of presenting truthful insight regarding the food we put into our mouths and how it affects our health. And he’s a comedian too, which means that much of what he writes at least raises a smile.

The post I have linked to is Tom’s attempt, I think, to reveal just how misleading so-called ‘epidemiological’ evidence can be. Epidemiological studies, also known as ‘observational’ studies, essentially look at the relationships between things. For example, epidemiologists might look at the relationship between smoking and lung cancer or saturated fat and heart disease.

The fundamental issue with such studies is that even if two things are found to be linked, it does not mean that one must be causing the other. To use an example from Tom’s blog post, imagine if we find that egg-eating is linked with an enhanced risk of heart disease. Well, seeing as eggs have generally had an unhealthy reputation for the last 20-30 years, it’s entirely possible that health conscious individuals have gone off eggs, while those who don’t care much to act on health advice have not. And so any apparent link between egg-eating and heart disease might have nothing to do with eggs at all, but to do with the un-health-conscious behaviours of those who eat eggs (e.g. smoking and being sedentary).

There is a huge amount of epidemiological data in the scientific literature, and I would most certainly not dismiss all of it out-of-hand. But I most certainly take far less notice of it than intervention studies – studies where individuals are subjected to something (e.g. a drug, a food or a lifestyle change) to see what effect it has compared to a group who do not experience this intervention. It is these studies that tend to allow us to dissect the realities about what is healthy and what isn’t, and what works and what doesn’t.

I came across a study recently which showed that women eating more wholegrains had lower levels of something called C-reactive protein (CRP) in their bloodstreams [1]. CRP is a marker of inflammation, and higher levels of it are associated with enhanced risk of heart disease. This finding, on the face of it, might be used by some to justify perpetuating the notion that ‘wholegrains are good for the heart’.

Now, wholegrains enjoy a healthy reputation generally. I don’t care much for them myself, as evidenced by the fact that I eat hardly any grain at all (wholegrain or otherwise). But those who are health-conscious and believe wholegrains are healthy will tend to make some effort to include them in their diets. Might the lower CRP levels seen in those eating wholegrain have nothing to do with the wholegrains per se, and more to do with other habits associated with health-consciousness?

One way to perhaps find out would be to perform an intervention study. And as it happens, such a study has been done and published recently and I reported on it here. It found that supplementing individuals with wholegrain did not improve any risk factors for heart disease, including markers for inflammation. We should not conclude from this one study that wholegrain do not benefit heart health, but as I pointed out in the blog post I’ve linked to, there is also evidence that blood sugar-disruptive carbs (including some wholegrains) have been found to worsen heart disease risk markers.

Another supposed health benefit of eating wholegrain is that it reduces the risk of cancer of the colon. There is some epidemiological research to support this. But, again, when the theory has really been put to the test in the form of intervention studies, wholegrains have again been found wanting [2,3].

References:

1. Gaskins A J, et al. Whole Grains Are Associated with Serum Concentrations of High Sensitivity C-Reactive Protein among Premenopausal Women.. Journal of Nutrition 2010;140(9):1669-1676

2. Jacobs ET, et al. Intake of supplemental and total fiber and risk of colorectal adenoma recurrence in the wheat bran fiber trial. Cancer Epidemiol Biomarkers Prev. 2002 11(9):906-14

3. Alberts DS, et al. Lack of effect of a high-fiber cereal supplement on the recurrence of colorectal adenomas. Phoenix Colon Cancer Prevention Physicians’ Network N Engl J Med. 2000 20;342(16):1156-62

15 Responses to Why we can’t rely on epidemiological evidence

  1. Peter Silverman 30 September 2010 at 1:23 am #

    Rats who eat whole grains probably have lots of other healthy habits, like brushing their teeth twice a day, etc.

  2. Claire 1 October 2010 at 5:21 pm #

    Rats are omnivores! That means they’ll eat just about anything, including a human junk food diet and fat etc in drains and sewage with relish – regardless of whether or not it might be good for them.

  3. Reijo Laatikainen 1 October 2010 at 6:27 pm #

    I agree with John on epidemiological studies. However, we may have to live with them and with their defects becausse large randomized interventions are quite rare and difficult to control (and fund) in the field of nutrition. Much of the recent evidence opposing the negative independent effects of saturated fat come from epidemiological studies, though (Siri-Tarino et al. 2010, Mente A et al 2009).

  4. Nathaniel 1 October 2010 at 8:05 pm #

    A study has found that gray hair, male-pattern baldness, and wrinkles are all associated with heart disease. I’m not making this up.

    Time to buy some hair die, a toupee, and maybe some botox!

  5. Greg Carlow 1 October 2010 at 8:08 pm #

    A great example is

    Brightly coloured cars have lower fuel consumption than avaerage and this is true

    The wrong conclusion is that bright colours will improve fuel consumption. The correct conclusion is that large cars are generally restrained in colour or black, small cars are often brightly coloured.

    This one worked on my wife :-)

  6. kathy w 2 October 2010 at 1:14 am #

    What has been shown to be detrimental to colon health is red meat. I’d like to see a column about that.

  7. David Manovitch 2 October 2010 at 9:21 am #

    There’s a grain of truth in most nutritional stories, but is it a whole grain?

  8. Jill H 2 October 2010 at 11:43 pm #

    Seems to me what we have lost is the insightful observations of the relations between diet and health that were passed down over centuries of oral tradition. So that now when Jamie Oliver holds up a particular fresh fruit or vegetable to a class of school children they have no idea what it is. My mother would have said ‘eat those green beans – they are good for you’ though she would not have known why and my grandma would have said ‘fish is brain food’ without ever having heard of omega 3 fatty acids. I guess this is a kind of epidemiological study – they just knew what foods helped us thrive – cultural knowledge passed down through generations.
    This is the problem maybe with the kind of epidemiological studies carried out today – that they do not seem to take into account such things as age, sex, race and cultural diversity and then are subject to interpretation and interpretation often depends on point of view (and in the case of food companies point of view can reflect vested interests). Too firmly held opinions also might cloud the ability to look at new findings.
    I may find my mother was wrong about the green beans and grandma was wrong about the fish – but for the time being I think I will continue to trust their wisdom and keep eating them.

    Greg – I love your example and can’t help thinking where would a bright red ferrari be placed?

  9. Xenia 3 October 2010 at 9:08 am #

    Yes, we should not conclude from this study that whole grain does not benefit heart health. We should conclude it from the fact that we should not eat grain, any grain, ever, at all, in the first place, because just like soy, it is not suitable to be called a food or to be a food, at least not for humans. It has been shown over and over again, both in studies and in real life that it is detrimental to our health in too many ways to even begin to list.

    Whole grain is not better – and is sometimes worse. True, we should avoid refined grains (and other refined stuff) at any cost. Bot nobody seems to ever think about the fact that, if the grain remains whole and that very same grain is not organic (and 99% of grain is NOT), then all the pesticides, herbicides, fungicides, insecticides, toxic fertilizers etc. which would have otherwise been removed with the husks where they accumulate, remain in the flour when the grains are milled. So with shole grain that is not organic, you are ingesting 10 or 20 times as many toxic chemicals as you would otherwise.

    Then, there is gluten. I will not even go into that.

    And lastly, there is the fact that our digestive tract lining is very thin and easily damaged. It consists just of one layer of cells – so that the digested food can be more easily absorbed from the intestines into the tiny blood vessels surrounding it. You should never, ever eat roughage. Never. We are not meant to eat insoluble fiber that we cannot digest because it scars and damages the sensitive lining. This may cause bleeding, deteriorate absorbtion of nutrients and offer breeding ground to bad bacteria that find shelter in the scars – where they are not meant to be. It also increases inflammation, if repeated every day. But worst of all, it gradually creates spacing between the single-layer cells of the lining, leading to leakages of non-digested food particles into the tissues surrounging the intestine which is the best way if you want to invite allergies into your life, not to mention fatigue, pain, inexplicable headaches, insomnia and last but not least, autoimmune disorders.

    So stay away from whole grains and any other insoluble fiber. The way to get your fiber is with vegetables (and it is on purpose that I am not mentioning fruit here – today’s fruit is very far away from what Nature intended it to be …). People find it difficult to give up their bread and pasta so they found a way to justify it. But this does not make whole grain healthy. The reason epidemiological studies may sometimes find seeming health benefits in subjects eating whole grains is that such people who make the effort to eat whole grains instead of the refined ones also eat other stuff percieved as healthy and are generally more mindful of their diet and their lifestyle.

    The best rule (but of course not the only one) to judge what is healthy and what is not is to ask yourself if this food could be eaten raw. It does not mean that you have to eat it raw but if it could be ingested raw in case you wanted to, then it is a good start. For example, fish can be eaten as sushi, olive oil does not have to be cooked since you can use it on a salad, vegetables can be eaten raw, meat can be eated as carpaccio or steak tartare … There are other considerations, like how we prepare it, how it has been grown/raised etc. but the “raw rule” is a good start.

  10. Xenia 3 October 2010 at 9:13 am #

    Sorry, there is a typo at the end of the second paragraph above. “Shole” grain should of course be whole grain.

  11. Xenia 3 October 2010 at 9:19 am #

    @ kathy w:

    Red meat has never been found to be detrimental for ANYTHING. The reason is because it is not.

    Humans have been eating read meat for millions of years. They are still alive today. Barely, but that is another issue altogether … However, there would be no humans today, or no colons, if red meat were indeed detrimental for our colons.

    What is detrimental for colon is processed meat, cured meat and any meat, red or not, that is not raised naturally (i.e. in the wild, or at least pastured). Also, to eat it just cooked all the time is not the best idea in the world.

  12. Jill H 3 October 2010 at 11:42 pm #

    For sure, early humans could have taught us about healthy eating – fruit, berries, green leaves, roots,nuts, seeds – the odd wooly mammoth – and it all was eaten raw. Too often though there was not enough. Fire was a turning point in the human diet – it perhaps made mammoth steaks tastier and it did enable people to eat things they could not have without cooking and made preserving of meat possible. Herding techniques developed 20,000 years ago so animals could be reared and bred for their milk, meat and skins and then 10,000 years ago came the realization that food could be grown in our own back yard and agriculture had arrived – the cultivation of grain came a few thousand years later and our diet was pretty much established.
    Perhaps it is just not a good idea to look for the ‘magic bullet’ to improve our Western diet. In a traditional diet – it is the synergy of these foods – so probably a person who decides to include a whole grain such as oats in their diet which would contain more of the soluble gel like pectins, gums and mucilages and less of the insoluble type of fiber, in small amounts, along with lots and lots of green vegetables and meats from pastured animals and sustainably caught fish and who recognised that eating locally and/or organic, if you are able to, is eating from healthy soils nourished by organic matter rather than synthetic fertilizers and sprayed with pesticides, is a good thing because through a long process of trial and error, cultures eating this diet have found a way to stay healthy with what nature had to offer where they were.
    The ancient way of eating soy in the Asian diet of fermenting the beans is far from the way soy is used in the Western diet of including it in just about everything and feeding it to animals not designed to eat it along with corn, and is not traditional and, along with modern wheat, seems very high on the list of more modern foods that people may become allergic to.

  13. Lucien 4 October 2010 at 10:07 am #

    Dear Xenia,

    There is no evidence that processed meat is
    detrimental to the colon either. The few epidemiological studies that have asked the question ( on the basis of very poor data )
    have been inconclusive.

    On the other hand, if processed meat or any kind of meat had a measurable impact on colorectal cancer, vegetarians who never consume these would
    have fewer cancers than omnivores. Which they do
    not. In fact in the recent EPIC study carried out
    under the auspices of Oxford University, colorectal cancers were more frequent among
    vegetarians. For me that settles it.

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