There is nothing I like more than finding out that something that has been widely believed for decades is wrong. The cholesterol myth fits the pattern of so many items in my blog: it sounds good, it superficially makes sense, and there is a biologically plausible explanation, but when put to the (scientific) test, it fails.
This book covers blood levels of cholesterol, cholesterol in the diet, and drugs to lower cholesterol, and while not everything we hear is a myth, a lot of it is. The authors make the following claims, and support them with good references to key articles.
Firstly, the relationship between blood cholesterol levels and heart disease is, at best, weak and certainly more complicated than often portrayed. Half of patients with heart attacks have normal cholesterol levels, and half of those with high cholesterol have heart disease. Also, the simplification of ‘good’ cholesterol and ‘bad’ cholesterol is much more complicated than most people think, as there are good types of bad cholesterol and vice versa. Also, this complex association with heart disease is weak compared to other associations such as smoking. There are associations there, and these are currently being clarified, but the association with your overall cholesterol level is weak.
The most important message is that regardless of the complex correlation between blood levels of certain cholesterols and cardiac risk, there is no correlation between dietary intake of cholesterol and blood levels. Despite this, government bodies still recommend restricting dietary cholesterol. This assumed correlation is an example of conclusion jumping and oversimplification, the evidence behind it provides good examples of bias in research and policy making, and the result of pushing this myth is a good example of the law of unintended consequences
Like almost anything stored and produced in the body, the level of cholesterol is regulated by a complex homeostatic mechanism. Cholesterol is vital for many bodily functions and makes up the walls of our cells and many of our hormones. It is produced from scratch (mainly in the liver) and absorbed from cholesterol in our diet. If we eat more, our body produces less. If we eat less, the body produces more. Specifically, dietary saturated fats are not bad for you, and the alternatives (such as hydrogenated vegetable fats and sugar) are worse.
The unintended consequences come from the use of statins (cholesterol lowering drugs). The effect they have is not necessarily mediated by any effect on cholesterol levels (they possibly work via an anti-inflammatory effect). They are only effective in a restricted population (in high risk middle-aged males who have had a heart attack), but even then, they have no effect on all cause mortality and they have significant side effects. Yet, statins are seen as the answer to the problem of heart disease because of the sheer weight of marketing and lobbying behind them and because of our (misguided) belief that blood cholesterol levels are correlated with heart disease. The presence of statins and the amount of money at stake is one of the reasons the cholesterol myth is perpetuated.
Statin drugs block cholesterol production. For such an important substance, how could we think that blocking production of something that does not directly cause heart disease, and something that is so important for the function of our body, would not have unintended consequences. The side effects are not uncommon and are important, including sexual dysfunction, memory loss, muscle dysfunction and diabetes.
Another repeated point is one that I have made before. Although some of the studies reported in this book show some benefits, they repeatedly show no benefit in overall (all-cause) mortality. See my earlier blog post for why this is the most important outcome.
The more likely culprits causing heart disease are discussed, including sugar, inflammation and insulin resistance.
The last part of the book covers sugars, other dietary factors and stress, and gives recommendations for heart health. The evidence offered regarding eating berries and dark chocolate, as well as laughing and crying (for example), is not convincing and I found this section disappointing, given the high evidence level the authors (rightly) demanded from the cholesterol literature. The book would have been stronger if it finished a few chapters early and stuck to debunking the cholesterol myth. If you have proved that someone is innocent, finding other suspects does not strengthen your case.
The bottom line
These two authors are not alone in their opinion that cholesterol is not a direct culprit in heart disease, that dietary cholesterol does not influence heart disease or longevity, and that statins are overprescribed and their side effects are under-reported. Their arguments are sound, but turning the cholesterol ship around will take some time.
Title: The Great Cholesterol Myth (2012)
Authors: Jonny Bowden and Stephen Sinatra
Publisher: Fair Winds Press
Dr Skeptic an is academic surgeon with an interest in the scientific evidence for the true effectiveness of medical practice, as opposed to the perceived effectiveness, and why there is a difference between the two.
Visit his blog http://doctorskeptic.blogspot.com.au/