The Skeptical Cardiologist recently gave a virtual presentation for St. Louis University School of Medicine Grand Rounds on recent studies examining the therapeutic benefit of omega-3 fatty acids and fish oil supplements.
The talk is about 45 minutes and is absolutely mesmerizing. Just kidding. Actually, I’m always amazed at how oddly and slowly I speak even when I’m totally at ease and know the topic backwards and forwards.
I began by indicating that I would be talking on a weirdly interesting topic that spans nutrition, business, the nutraceutical-industrial complex, quackery, and preventive cardiology and yields fascinating insights into the glaring weaknesses of nutritional epidemiology, the hidden weaknesses of randomized clinical trials, and the many sources of bias in scientific research.
Here’s the video of my talk, which was followed by about 30 minutes of questions and comments, including a discussion on cooking oils.
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What I addressed can be boiled down to a question most of us over the age of 40 have asked ourselves: Should I take fish oil supplements to prevent cardiovascular disease?
Although almost all my academic research and publications have been in the field of echocardiography, for the last dozen years I have evolved into a clinical cardiologist with major interests in preventive cardiology and enlightened medical management of atrial fibrillation.
Over the years, I’ve cultivated a healthy skepticism for medical and scientific information that has potential bias.
To educate my patients, myself, and the public at large, I started writing a blog in 2013. I began by looking at the scientific underpinning (or lack thereof) of current dietary guidelines relating to cardioprotection.
One of the first topics I tackled was fish oil supplements, which seemed to have solid scientific and guideline support. Before I looked deeply into the topic, I was advising patients with coronary artery disease or at high risk for it to take fish oil supplements; but after I delved into the evidence, I began taking patients off them.
The fish oil story began with observations that Eskimos in Greenland who consumed an extremely high fat diet rarely had evidence of coronary heart disease.
In the ’70s, two Danish doctors, Hans Olaf Bang and Jørn Dyerberg, went to Greenland because they’d read there were very low levels of cardiovascular disease among the Inuit eating seals and whales and fish.
When they did blood lipid analyses of Inuit samples, they found very high amounts of omega-3 fatty acids and formed a hypothesis that omega-3s might be responsible for the lower levels of coronary heart disease among Greenland Inuit.
These observations have triggered tens of thousands of studies which have attempted to determine if omega-3 fatty acids (OMFAs) are the key to cardiovascular protection.
In the last 40 years, there has been a pronounced movement to proclaim all saturated fats as bad and all polyunsaturated fatty acids (PUFAs) as good. Simplifying nutritional advice in this way makes for simple public health messaging but blurs the truth. For example, there is no solid evidence that dairy fat, which is predominantly saturated, has any negative cardiac effects.
Likewise with PUFAs, many researchers have concluded that humans are consuming far too many of omega-6 PUFAs, which are predominantly obtained from corn, safflower, and soybean oil. Canola oil, a product of factory ultra-processing and genetic manipulation is widely promoted as very good for the heart.
The omega-3 family consists of long-chain (18 to 22 carbons) PUFAs with a double bond at the third carbon from the omega end. The marine OMFAs of interest are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are predominantly derived from seafood consumption
DPA levels aren’t associated with fish consumption and have minimal relevant physiologic 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 instead produced internally from alpha-linolenic acid. Alpha-linolenic acid is an 18-carbon essential n-3 PUFA derived from plant sources.
In addition to long-chain-3 PUFA, fish provide specific proteins, vitamin D, selenium, and other minerals and elements.
Observational studies have demonstrated that greater dietary consumption of either fatty fish or omega-3 fatty acids is associated with fewer incident cardiovascular events and that circulating concentrations of EPA or DHA inversely correlate with cardiovascular risk.
Of course, all these studies did not prove that eating fish or taking OMFA supplements reduces your risk of CVD.
This doesn’t stop press releases and news stories related to these observational studies from promoting them as showing causality and implying an important role for supplementation in reducing heart disease. Nutrition guidelines from the American Heart Association in 2005 co-authored by Bill Harris, MD, arguably the world’s foremost expert on OMFA concluded that everyone in the population should eat “a variety of (preferably oily) fish at least twice a week” and that their diet should include “oils and food rich in ALA (flaxseed, canola and soybean oils, flaxseed and walnuts).”
What are the “oily fish” all Americans should be consuming twice per week? The amount of EPA+DHA in the recommended portion size of 3.5 oz of fish varies wildly.
To make things more complicated with fish consumption, one has to consider mercury content and the sustainability of the species one is consuming. The Environmental Defense Fund has a seafood selector that rates each type of fish on these three items. But even within a single type you might think would be incredibly healthy — the mackerel — the levels of mercury vary wildly depending on the specific species.
As a result, most Americans threw up their arms in frustration and confusion and, prodded on by a burgeoning fish oil supplement industry freed from any regulatory constraints by legislation in 1994, they began buying millions of fish oil supplements.
Thus began the era of fish oil as snake oil, promoted widely by quacks like Dr. Oz who recommended “FISH OIL FOR ALL!”
At this point in the presentation, I detailed recent large randomized controlled trials of high-dose omega-3 fish oil supplementation. Spoiler alert, the STRENGTH trial found no cardiovascular benefits.
Along the way, I touched on the weaknesses of observational epidemiology and the sneaky ways the fish oil supplement industry biases scientific publications.
My conclusion was that there is no compelling evidence for taking-over-the-counter fish oil supplements for primary or secondary prevention of cardiovascular disease.
I also discussed the reasons to question the benefits of icosapent ethyl (Vascepa), which were demonstrated in the REDUCE-IT trial, and why there needs to be another trial that compares icosapent ethyl to a neutral oil like corn oil rather than mineral oil.
Just prior to giving my talk 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 I believe brings us full circle in our OMFA journey.
Anthony C. Pearson, MD, is a noninvasive cardiologist and professor of medicine at St. Louis University School of Medicine. He blogs on nutrition, cardiac testing, quackery, and other things worthy of skepticism at The Skeptical Cardiologist, where a version of this post first appeared.
Last Updated January 17, 2021
Source: MedicalNewsToday.com
