Wednesday, April 21, 2010

Eat your fish!

I spend a lot of time thinking about fish. I work in a fisheries genetics lab, I love eating and cooking fish, and I live in Seattle where local salmon are essentially rock stars. But a recent continuing-education lecture at work got me thinking: am I eating enough fish? Should I be eating more?

The speaker was Dariush Mozaffarian, a cardiologist who has studied the health benefits of a high-fish diet. He was charismatic and engaging, and I found the topic much more interesting than most of the statistics-heavy Powerpoint presentations geared towards marine science PhDs that go right over my head at work lectures. But this--this was a topic I could get behind! I took a ton of notes, so read on if you're interested in the nitty-gritty. If not, just skip to the bottom line below.

Here's what Dr. Mozaffarian said, with some of my commentary in parentheses:

We usually think of high cholesterol, diabetes, and hypertension as the causes of heart disease, but they are really all intermediate steps. The root causes are poor diet, inactivity, smoking, and poor lifestyle choices. Half of first heart attacks are fatal, so we need to prevent them from happening in the first place and not just treat warning signs. Instead of focusing on treating the warning diseases with medications, we should focus on changing unhealthy lifestyles.

However much we'd like to blame fatty foods, a diet high in saturated fat has been shown to have no effect on the rate of cardiac death. You might be less healthy with a high fat diet, but you won't actually die more often. (I wish I'd written down the study he cited!) This may seem contrary to what you've been told, but nutritional recommendations change as the science changes.

Essential dietary habits for cardiovascular health are, in this order: eating seafood/omega-3 fatty acids is most important, then no trans fat, then eating whole grains / fruits and vegetables / nuts and seeds / lower salt. A high seafood diet has the best evidence for stopping arrhythmia and reducing cardiac death—but note that we're only talking about benefits for cardiac health here, not endocrine system, liver, etc. This guy is a cardiologist, after all.

Wild trout and salmon, photo by mrjorgen

The highest quartile of fish eating (specifically blood levels of EPA and DHA, the helpful compounds in omega-3 fatty acids from fish) is linked to a 90% reduction in risk of sudden cardiac death—that’s huge! Another way to say it is that NOT getting enough omega-3s is a tenfold increased risk in cardiac death. (By the way, omega-3s in walnuts and flax seed are good, but they're made up of a different type of fatty acids and are not the same, healthwise--fish is better.) Studies of how much EPA and DHA people eat vs. the cardiac benefits show that the most "bang for your buck" is at consuming 250 mg per day, which correlates to a 1/3 reduction in cardiac death. How many servings that is depends on the type of fish, but it's generally eating quite a bit of fish over the course of a week, although not an extraordinary or inedible amount.

Now one of the most well known drawbacks to eating a lot of fish is high levels of mercury. Mercury released by coal plants and industrial waste bioaccumulates into the biggest fish, which we then eat. The speaker spent a lot of time downplaying the harm of mercury consumption: no published study has ever shown a statistically significant increase in cardiovascular risk as a result of mercury consumption in adults. (As far as I know that's not really the point: mercury doesn't affect the heart much at all. The real problem is in the brain, lungs, and kidneys.) Eating high mercury fish is possibly worse than eating low mercury, but eating more fish, of either type, is more beneficial to overall cardiovascular health in adults. So just eat a variety of species, try to minimize mercury if possible, but don’t worry so much about it that you stop eating fish altogether.

Another problem with fish eating is the possible accumulation of toxins such as dioxins and PCBs. A 2004 study showed farmed salmon to be higher in toxins than wild salmon, but the increased cancer risk from these toxins is far outweighed by the benefits in preventing cardiac death, so in the tradeoff of risks and rewards it's really worth it. From a purely individual health point of view, farmed salmon is actually better for you because it is fattier, and the increased toxins are less important than the added omega-3 fat. This also means that you can eat less of it and still get as much cardiac benefit. (This point pretty much totally freaked out all the marine biologists in the room, who are used to evaluating farmed salmon by its environmental impact, which is horrendous. If you want to eat a high fat fish, just buy fattier species of salmon such as coho or chinook. Hell, I would even buy the comparatively low-fat pink or chum salmon over farmed salmon. Just say no to rampant environmental degradation! Okay, end rant.)

Salmon filet, photo by Elana's Pantry

Now most of this data has been "for average adults" and it should be pointed out that pregnant women and babies have different needs. Babies actually need a higher amount of DHA than adults, and studies have shown that a mother’s DHA consumption during pregnancy is significantly correlated to the child’s IQ score and motor functions at eight years old. That's pretty crazy. However, mercury is also much more dangerous for pregnant women and young children, so these groups should avoid very high mercury fish while still eating plenty low-mercury seafood. Avoid: shark, swordfish, king mackerel, gulf of Mexico tilefish, and orange roughy, and limit albacore to no more than once per month.

A side note on fish oil: Fish oil as an omega-3 supplement is okay, but it’s better to eat real fish because we don’t know what the other components of fish might do together with the omega-3s and it's better to eat it as found in nature. Pregnant and nursing women should have 300 mg DHA per day (that’s a lot!), and so they might benefit from fish oil because it’s really hard to eat that much fish.

So what about sustainability? Sadly, in a room full of conservation biologists, Dr. Mozaffarian said relatively little. He asserted that both aquaculture and wild fishing are beneficial to human health, and the world’s dietary needs will only be met with increased fishing from both. As a society, we also tend not to look at the sustainability of our overall diet: choosing a steak over farm-raised salmon is actually more environmentally damaging. (Well okay, possibly, although it’s a bit like comparing apples and oranges. But shouldn’t we take even small steps to make more environmentally responsible choices? Baby steps, people.) He also pointed out that consumers are often confused as to whether a fish has been “redlisted” for enviornmental or health reasons. He’d like to see a grid of fish choices, with axes for environmental harm and cardiovascular health benefits. Fish such as sardines and anchovies belong in one corner for low environmental damage and high health benefits, but those shouldn’t be the only fish that people eat. (I think his point here is that people should feel okay about making choices that are personally helpful but environmentally damaging? Although we do that all the time, this isn’t a life philosophy I can generally get behind.)

Pan-fried sardines, photo by avlxyz

So here’s the bottom line:

Eat fish. It’s important to cardiovascular health to get enough omega-3s, and fish are the best source. In general, the highest omega-3 fish are the fattiest, such as salmon, anchovies, herring, sardines, trout, and albacore tuna. Keep mercury and toxins in mind when choosing which species to eat, but it’s best to just eat a wide variety and don’t worry about it too much. In my opinion, it’s also important to keep environmental sustainability in mind; check out Monterey Bay Aquarium’s Seafood Watch guide for recommendations. Whatever type it is you like though, just eat your fish!


  1. How about adding a link to the Monterey Bay Seafood Watch guide so folks can click on your words and go right to the pocket version?

  2. Oops, meant to in the first place and just forgot. Thanks for the reminder!

  3. As someone who works for a watchgroup that deals with aquaculture, even Monterey Bay Aquarium isn't always on their game and much MSC-certified fish is really just greenwashed bad aquaculture practices. Food & Water Watch publishes a guide that is much less specific with regard to species, but tells you what you need to look for in order to avoid buying fish brought to you by the worst environmental practices:

  4. That was Emily, by the way.

  5. I'm trying to stay on top of this subject, and appreciate your sharing this info. Just to add to what you said: Omega-3 is also known to protect the heart (from cholesterol for sure, and in other ways I think) and because it has anti-inflamatory properties, it helps with inflamation issues - including arthritis: my arthritis is tons better now that I'm taking Omega-3 every day and eating salmon and tuna (the kind you told me about with the American flag on the can- thank you!)1-2/week,....Also, it is very possible that Omega-3 can help prevent Alzheimer's Disease because of its anti-inflamatory properties (good for all of us to consisder, but especially the Bliss kin because of our family history). FORGIVE me if I'm repeating anything in your notes from the doctor's talk, Alana - I haven't ready the whole post yet, (just read your summary so far)-- plan to read it all after I do my stretching/strengthening exercises that should have done MUCH earlier today! xoxo

  6. An easy way to estimate your mercury exposure from eating fish is to check out the free online mercury calculator at Based on the current U.S. EPA and FDA guidelines, the mercury calculator is an excellent way to know your potential mercury exposure risk.



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