Friday, January 15, 2010

Saturated Fat Is Not Associated With CVD, Evidence of Publication Bias

by Chris Masterjohn

A recent meta-analysis in the American Journal of Clinical Nutrition pooled together data from 21 unique studies that included almost 350,000 people, about 11,000 of whom developed cardiovascular disease (CVD), tracked for an average of 14 years, and concluded that there is no relationship between the intake of saturated fat and the incidence of heart disease or stroke. In fact, the "risk ratio" for the development of CVD as intake of saturated fat increased was 1.0, meaning that people who ate more saturated fat were no more or less likely to develop CVD.


The authors also used a funnel plot to show that smaller studies more prone to error were more likely to show an association between saturated fat intake and CVD than were larger studies less prone to error. 

In the picture below, each square or diamond represents a study. If it is to the right of the vertical line down the middle, it reported an increase of CVD risk with increased intake of saturated fat. If it is to the left of the vertical line, it reported a decrease in risk. The studies plotted towards the top were larger and the studies plotted toward the bottom were smaller.




If there is no publication bias, we would expect the studies to be distributed symmetrically around the average result of the total pooled data (in this case, a risk ratio of 1.0, meaning no effect). Publication bias tends to affect smaller studies — everyone wants to know the results of large, expensive, extensively publicized studies, but small studies will often go unpublished or ignored if they have negative results. In the picture, you can see that the smaller studies were greatly skewed towards finding an increase in CVD risk with increased intake of saturated fat, while the larger studies were more likely to find no effect. 

This does not prove, but suggests, that many small studies went unpublished or otherwise lost down the memory hole if they found no association or a negative association between intake of saturated fat and risk of CVD.

All in all, however, we must remember that correlation never demonstrates causation. As I will be discussing in the upcoming sequel to my
PUFA Report, the controlled intervention trials substituting polyunsaturated fats for saturated fats suggested that replacing foods like butter with foods like vegetable oil would increase the risk of cancer and possibly even hasten the development of atherosclerosis.

It will be interesting to see how extensively the media publicizes this analysis — or will it be ignored?


Read more about the author, Chris Masterjohn, PhD, here

19 comments:

  1. Seems to me like the media is ignoring it. I've only seen you and a few other bloggers talking about it. Of course, the media will often bend to the wishes of advertisers, who of course have all kinds of low- and non-fat items to market...

    ~Dave
    www.DaveSoucy.com

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  2. Dave,

    Very true! Thanks for reading and commenting!

    Chris

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  3. R u guys kidding?! MEN'S HEALTH COVERED IT!!

    http://drbganimalpharm.blogspot.com/2010/01/krauss-in-house-low-fat-message-was.html

    Keep up the excellent work Chris.

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  4. It may be in Men's Health, but I haven't seen it anywhere else. I think the media non-response goes beyond what sponsors want and into the realm of "does not compute" for most people. That is the response I often get when mentioning studies like this one. People are now thoroughly imprinted with the saturated fat/cholesterol dogma. It's like telling them the moon landing didn't happen.

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  5. Taube's book, Good Calories, Bad Calories, tells us how this body of "knowledge" gets the way it does and why we are told what we are told. I am fascinated by meta-studies that demonstrate different results than individual studies. I teach social science researchers how to be good consumers of research and know what all of us readers should know (and aren't taught in school ever, but don't get me started). This will be added to my readings. Thanks.

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  6. The health authorities are fully aware of the serious flaws and omissions in this meta-analysis. This study was funded by the National Dairy Council, dairy being the number one source of saturated fat in the U.S. and many other parts of the world. It was also conveniently published just before the USDA lowered the dietary recommendations of saturated fat for the first time in 20 years, from 10% to 7% of total calories.

    Below is a section from the statement released by the European Heart Network in regards to their opinion of this meta-analysis, titled “European Heart Network position piece: Impact of saturated fat on cardiovascular disease obscured by over‐adjustment in recent meta‐analysis”

    “However, the meta‐analysis (and an accompanying opinion piece by the same authors (4)) is compromised by a number of serious flaws and omissions.”
    “The most serious of these flaws is an over‐adjustment for serum cholesterol levels.”
    “Adjustment for serum cholesterol levels will inevitably bias the results of the meta-analyses towards finding no association between dietary saturated fat intake and cardiovascular disease, but the authors do not mention this limitation in their article.”
    “As Jeremiah Stamler asserts in his editorial, what was actually found by the meta-analysis was ‘a statistically non-significant relation of SFA [saturated fat] to CHD... independent of other dietary lipids, serum lipids, and other covariates’. A more appropriate and informative analysis would have included non-adjusted associations between saturated fat and cardiovascular disease. An examination of the forest plots provided in the article shows that those cohort studies that did not adjust for serum cholesterol levels were more likely to find a positive association between saturated fat intake and cardiovascular disease, suggesting that a meta-analysis of unadjusted data would likely produce positive results.”

    The full statement from the European Heart Network can be found below with references to studies that show a positive relationship between saturated fat and heart disease:
    http://www.sydan.fi/lehtiarkisto/sydan_210/artikkelit/fi_FI/elainrasvat/_files/83538765767049682/default/EHN%20position%20piece%20-%20sats%20meta%20analysis.pdf

    Below is a published study showing reversal of severe heart disease backed up with angiogram evidence.
    http://www.heartattackproof.com/resolving_cade.htm

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  7. What a great info thanks for sharing

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  8. That's why people on islands who had coconut in their diets never developed heart diseases.

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  9. Great post! This blog is very informative. Thanks for giving us info about Saturated Fat.

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  10. I learned something from your post about Saturated Fat. This a great help for me. Thanks for posting!

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  11. Sometimes who holds in science about the food especially in WHO makes things complicated and even giving us people the confusing ideas to consider.

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  12. Thanks for the nice information sharing. I love to visit your blog regularly.

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  13. Great study!

    Thanks for sharing your thoughts. very informative!

    You'd love to hear more from you guys! :)

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  14. Hi.Chris.thanks for this post about saturated fat.but i think people might have it for personal opinion and interest.

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  15. Well i wasn't ware of this thanks alot for sharing !

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  16. I completely agree with these viewpoints. I have personally lived on the low-fat high carb diet for almost 30 years and yet kept gaining weight and had a completely screwed up lipid profile. The Dr. almost put me on statins and thats when I decided to take matters in my own hands and started investigating exercise and good fats for heart health. I was of course shocked to not find a single piece of evidence that correlated dietary cholesterol to lipid cholesterol. I then started investigating saturated fats and still couldn't find any evidence that saturated fat will cause heart attacks. I think when it comes to heart disease most of the medical community works off of hearsay where a doctor goes up on stage and announces, as-a-matter-of-factly, that cholesterol and saturated fats cause heart attacks and then the other doctors cite the previous doctor in their publications and so on and so forth. Its a vicious circle that's been perpetuated for the last half a century and its time the medical community come clean. I highly doubt that's ever going to happen given the fact that demonizing cholesterol has created a $26 billion industry of statin drugs that sponsors more research in this area. If you are a medical researcher serious about your career you better not say anything that will go against conventional wisdom of "cholesterol is evil" otherwise your grants will be cut and you will never publish any thing ever again. So from that standpoint I think the situation is abysmally bleak, but thanks to people like you there is some hope for people that are willing to take health matters in their own hands. Thanks for taking the initiative to educate the ordinary people about whats healthy and whats not!

    Regards,

    Yogesh Verma
    inutrifit.com

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