The skeptical cardiologist recently gave a virtual presentation to the Grand Rounds of the St. Louis University School of Medicine on recent studies examining the therapeutic benefits of omega-3s and fish oil supplements.
The lecture takes about 45 minutes and is absolutely fascinating. Was just a joke. Actually, I am always amazed at how strangely and slowly I speak, even if I feel totally at ease and know the subject back and forth.
I started by saying that I was talking about a strangely interesting topic that encompasses nutrition, economics, the nutraceutical-industrial complex, quackery and preventive cardiology, and provides fascinating insight into the glaring weaknesses of nutritional epidemiology and the hidden weaknesses of randomized clinical trials, and the many sources of bias in scientific research.
Here is the video of my talk, followed by about 30 minutes of questions and comments, including a discussion on edible oils.
What I have mentioned can be reduced to a question that most of us have asked ourselves over 40 years: Should I take fish oil supplements to prevent cardiovascular disease?
Although almost all of my academic research and publications have been in the field of echocardiography, over the past twelve years I have grown into a clinical cardiologist with a keen interest in preventive cardiology and enlightened medical treatment for atrial fibrillation.
Over the years I have developed a healthy skepticism about medical and scientific information that is potentially biased.
To educate my patients, myself, and the public, I started blogging in 2013. I started by looking at the science behind (or lack of) the current dietary guidelines for cardioprotection.
One of the first topics I brought up was fish oil supplements, which appeared to have solid scientific and guideline support. Before delving into the subject, I advised patients with coronary artery disease or at high risk to take fish oil supplements; But after looking at the evidence, I started taking patients from them.
The fish oil story began with the observation that Eskimos in Greenland on an extremely high-fat diet rarely showed signs of coronary artery disease.
In the 1970s, two Danish doctors, Hans Olaf Bang and Jørn Dyerberg, traveled to Greenland because they had read that the Inuit who eat seals, whales and fish have very few cardiovascular diseases.
When they performed blood lipid analyzes on Inuit samples, they found very high levels of omega-3 fatty acids and hypothesized that omega-3 fatty acids may be responsible for lower levels of coronary artery disease in Greenland Inuit.
These observations have sparked tens of thousands of studies trying to determine whether omega-3 fatty acids (OMFAs) are key to cardiovascular protection.
There has been a marked movement over the past 40 years to label all saturated fats as bad and all polyunsaturated fatty acids (PUFAs) as good. Simplifying nutrition counseling in this way allows for a simple public health message, but it blurs the truth. For example, there is no solid evidence that milk fat, which is mostly saturated, has adverse effects on the heart.
With PUFAs too, many researchers have come to the conclusion that humans consume far too many omega-6 PUFAs, which are mainly obtained from corn, safflower and soybean oil. Rapeseed oil, a product of the factory’s ultra-processing and genetic engineering, is widely advertised as being very good for the heart.
The omega-3 family consists of long chain (18 to 22 carbon atoms) PUFAs with a double bond on the third carbon atom from the omega end. The interesting marine OMFAs are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are mainly obtained from the consumption of seafood
DPA levels are not associated with the consumption of fish and have minimal relevant physiological or clinical effects. DHA is a primary structural component of the human brain, cerebral cortex, skin, and retina. For organisms that do not eat algae or animal products containing DHA, DHA is made internally from alpha-linolenic acid instead. Alpha-linolenic acid is an essential n-3 PUFA with 18 carbon atoms that is obtained from vegetable sources.
In addition to the long-chain 3-PUFAs, fish provide specific proteins, vitamin D, selenium and other minerals and elements.
Observational studies have shown that higher consumption of either oily fish or omega-3 fatty acids is associated with fewer cardiovascular events and that circulating levels of EPA or DHA are inversely correlated with cardiovascular risk.
Of course, all of these studies haven’t proven that consuming fish or taking OMFA supplements reduces your risk of cardiovascular disease.
This does not prevent press releases and news related to these observational studies from promoting them as evidence of causality and as an important role of dietary supplement in reducing heart disease. The 2005 American Heart Association Dietary Guidelines, co-authored by Bill Harris, MD, arguably the world’s foremost expert on OMFA, concluded that everyone in the population “had a variety of (preferably oily) “Should eat fish” and your diet should include “oils and foods rich in ALA (flaxseed, canola and soybean oils, flaxseed and walnuts)”.
What Are the “Oily Fish” All Americans Should Eat Twice a Week? The amount of EPA + DHA in the recommended serving size of 3.5 oz of fish varies widely.
To make fish consumption difficult, one has to consider the mercury content and the sustainability of the species one is consuming. The Environmental Defense Fund has a seafood selector that rates each fish species on these three points. But even within a single species that you might find incredibly healthy – the mackerel – mercury levels vary widely between species.
As a result, most Americans threw up their arms in frustration and confusion and began buying millions of fish oil supplements, spurred on by a burgeoning fish oil supplement industry that was liberated from all regulatory restrictions by law in 1994.
This is how the era of fish oil began as snake oil, used by quacks like Dr. Oz was widely promoted, the “FISH OIL FOR EVERYONE!” recommended.
At this point in the presentation, I have detailed the most recent large randomized controlled trials on high-dose omega-3 fish oil supplements. Spoiler alert, the STRENGTH study found no cardiovascular benefits.
Along the way, I addressed the weaknesses of observational epidemiology and the sneaky way the fish oil supplement industry skews scientific publications.
My conclusion was that there is no compelling evidence to support the use of over-the-counter fish oil supplements for primary or secondary prevention of cardiovascular disease.
I also discussed the reasons to question the benefits of icosapentethyl (Vascepa) proven in the REDUCE-IT study and why there needs to be another study comparing icosapentethyl to a neutral oil like corn oil rather than mineral oil.
Shortly before my presentation, I came across a study published in late 2020 that is the first prospective study in Inuit on the cardiovascular effects of long-chain n-3 polyunsaturated fatty acids. No effect was found, which in my opinion closes the circle on our OMFA trip.
Anthony C. Pearson, MD, is a non-invasive cardiologist and professor of medicine at St. Louis University School of Medicine. He blogs about nutrition, heart tests, quackery, and other skeptical things at The Skeptical Cardiologist, which is where a version of this post first appeared.
Last updated on January 17, 2021