The skeptical cardiologist has previously agreed with widespread dietary guideline recommendations that encourage most adults to consume a variety of fish, preferably oily types (eg, salmon, sardines, tuna, and mackerel), at least twice a week for the prevention of cardiovascular disease.
Much of my faith in fish and fish oil, however, was based on observational data and one randomized trial from the mid-90s in patients following heart attacks (the GISSI trial.) The strongest evidence for the benefit of eating fatty fish has always come from observational studies that show individuals with a higher intake of omega-3 fatty acids (EPA and DHA) and with a higher RBC level of EPA and DHA have lower CV risk.
By early 2021, based on several new trials of fish oil supplements I concluded (you can see my video presentation and summary here) that “there is no compelling evidence for you to take over-the-counter fish oil supplements for primary or secondary prevention of cardiovascular disease.” This is the same advice I have been giving since 2013
The STRENGTH study which showed absolutely no benefit of supplementing with EPA/DHA on reducing a compositive cardiovascular endpoint has triggered me to start looking more closely at the quality and strength of the evidence for the fish recommendations in general.
The PURE study found no significant association between fish intake and any health outcome after adjustment for known confounders.
These findings and an old Welsh randomized trial have caused me to question whether eating fish does, indeed, protect us against atherosclerotic complications like stroke and heart attack.
The Downsides to Fish Consumption
If there are no special benefits to fish consumption perhaps its limitations mean individuals don’t need to worry about consuming it twice a week.
Eating fish the FDA considers healthy requires studying charts like this one due to concerns about mercury intake. From the FDA’s “Advice about eating fish.”
There are other considerations that complicate the fish farrago. Many articles caution against farm-raised salmon due to a higher level of contaminants and a lower level of omega-3 fatty acids. But fresh wild salmon costs up to four times as much as farm-raised and these prices put it out of the reach of many Americans
Choose Your Poison?
My palm tree trimmer recently was kind enough to gift me a ziplock bag with a piece of fresh tuna he had caught the day before in the ocean nearby. It made for a wonderful meal but the FDA says I should have checked advisories before eating it and avoided fish for the rest of the week.
What about fish caught by family or friends? Check for fish and shellfish advisories to tell you how often you can safely eat those fish. If there is no advisory, eat only one serving and no other fish that week. Some fish caught by family and friends, such as larger carp, catfish, trout and perch, are more likely to have fish advisories due to mercury or other contaminants.
Some guidelines emphasize the manner in which your fish is prepared which makes a lot of sense. In restaurants, lots of fish is served as fish and chips wherein the fish is dipped in batter and deep-fried in oil or beef tallow. Clearly, the nature of the oil used for frying and how often this is changed could have a massive influence on the overall nutritional quality of the dish.
I hope to share my fishy analysis with you soon. In the meantime, I am dredging up the only post I have written on fish, written in 2017 and featuring an odd and SEO-unfriendly title.
Sheephead Fish: Vulnerable and Gender Fluid Yet Mighty Tasty
The skeptical cardiologist and his Eternal Fiancee’ have escaped dreary and oceanopenic St. Louis and are spending a week in allegedly sunny and definitely beachy San Diego.
Upon arrival we took in a Farmer’s Market in Little Italy and stumbled into Ironside Fish and Oyster.
Always in search of heart-healthy, unique and local fish dishes, I spotted on the menu a luncheon special of sheepshead fish.
California sheephead (Semicossyphus pulcher), turned out to be a fascinating and most delicious fish.
Before I could order it, I had to verify that I wasn’t contributing to the extinction of a species. The IUCN Red List of Threatened species lists the CS as “vulnerable” because:
“The natural history of this species, including its limited geographic range along inshore habitat, the likely increasing interest in the fishery and the currently unsustainable fishing levels (according to the models of Alonzo et al. 2004), together with the difficulties in enforcing existing regulations strongly suggest that this species will continue to decline if stronger protective action is not put into place. “
After learning the CS was vulnerable, I had to make a critical decision: should I eat it before it disappeared, robbing me of a chance to ever taste it, or should I order something that wasn’t vulnerable, thus contributing to the preservation of the continuing biodiversity of the planet. I elected to taste it.
Gender Fluid Fish
Further research revealed that the CS transitions from a reproductively functional female at birth, to a functional male during the course of a lifespan in response to social factors (?reverse Bruce Jenner).
According to evolution.berkeley.edu this is termed sequential hermaphroditism:
In some sequentially hermaphroditic fish species, animals develop first as male and then switch to female (a condition called protandry), and in others, the individuals develop first as female and then switch to male (protogyny).
Clownfish (as in Finding Nemo) do the opposite of the sheepshead and are protandrous:
This species lives within sea anemones in groups of two large fish and many small fish. The two large fish are the only sexually mature fish and are a male and female breeding pair. All of the smaller fish are male. If the large breeding female is removed, her male mate changes sex to female and the next largest fish in the group rapidly increases in size and takes over the role as the sexually mature male.
Do not make the mistake of looking at this youtube video while waiting for your sheepshead entree’ as I did. The disturbing human-like teeth will not be part of your meal.
Finally, the 4 ounces of CS arrived, perfectly prepared a la plancha,
with an accompanying lemon butter sauce that was divine. Although butter is not officially a big part of the Mediterranean diet, frequent readers of the skepcard now that dairy fat does not make you fat or promote heart disease, and is fine (in moderation of course) as part of a heart-healthy diet.
Speaking of lingering bad dietary advice, if you investigate the nutritional content of sheepshead at a site like SELF Nutrition, the old canard that we should be limiting our dietary cholesterol raises its ugly head. Because sheepshead contain significant amounts of cholesterol (presumably from carnivorously munching on shellfish with its scary human-like choppers), the misguided nutritionists at SELF Nutrition and other would-be nutritionistas pronounce it as not optimally healthy.
PS. If you’d really like to get your nerd on about sequential hermaphroditism check out this graphic showing the independent evolution of this feature across different phylogenetic lineages!
8 thoughts on “Is There a Solid Scientific Basis for Recommending You Eat Two Servings of Fatty Fish a Week?”
Thanks for a great article. I speared a few sheepshead back in my undergrad days at UCSD. Ugly but tasty! I have never seen it on a menu—Ironside gets some interesting things in. Hope you had a great time in San Diego–was it sunny? Sometimes people come im May/June and hit the May gray or June gloom. As a retired sedation dentist, I wonder if I should get a mercury test—-sometimes I feel “mad as a hatter”!
I had such a great time in San Diego over the years I eventually moved there!
Wonderful essay. Sheepshead fish are adorable, but I can’t remember any patients with similar-looking teeth (unless they only had canine teeth). I was crushed to see they can’t be found off Sheepshead Bay here in Brooklyn. I’m convinced if we followed recommendations on which fish were healthy and/or sustainable we wouldn’t eat any. Wasn’t there something maybe 40 years ago about PCBs in striped bass? Of course, given my occupational exposure to mercury I limit my consumption of fish with high mercury content. If only grilled swordfish weren’t so damned tasty!
My total cholesterol is 180 ,my LDL is 115, triglycerides, and HDL are in the normal range. So not terrible. Still my doctor is insisting I take Lovaza prescription fish oil. She says her calculator says those numbers put me at moderate risk of heart disease. I never filled the prescription. I didn’t take the bait(ha ha). I asked her to put me back on Zetia which lowered my numbers with no side effects and she won’t. Says Zetia is useless. I can’t take statins so I’m stuck. Perhaps when you eat fish you are not eating more fatty or processed meats if the fish is prepared/cooked properly and that’s the advantage. From my understanding fish and dairy products seem less problematical than red meat and even poultry when it comes to heart disease. Certainly fish is often contaminated and this is a concern. I do do the two times a week fish ritual(mostly wild salmon) but as you suggested, I also eat lots of fruits, veggies, nuts, olive oil and whole grains everyday and perhaps that is what keeps me healthy along with exercising . Thank-you for this post . These studies drive me crazy . Hard to know what the truth is .
It’s hard to understand your doctor’s thinking based on your description.
Lovaza would not be indicated in a patient with your lipid profile.
If you have an indication for LDL/cholesterol lowering and have not tolerated statins, zetia is a fine alternative.
The truth is hard to recognize but here at the skeptical cardiologist we specialize in it.
Thanks for responding . It reaffirms I don’t need to take Lovaza.
Hmm, not sure if I should eat a can of sardines twice a week and take a daily krill oil supplement. So eating fish is beneficial for those who have CV disease but is of no benefit to those without. Thing is, don’t we all have CV disease? https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2777338
I find this paper problematic because the authors have glommed together 3 disparate studies. The PURE study which was observational and two RCTs totally unrelated to omega-3, or fish consumption. All of this, of course, is retrospective.
As with all the observational fish (and fish oil) studies it is hard to say whether the modest effects on CV outcomes indicates causality or whether the healthy user bias or other unmeasured confounders created the small difference.
Those who are eating precisely 2 servings per week are highly likely to be following all the other good behavior things they have been told.