Is Eating Fish Safe? A Lot Safer Than Not Eating Fish! | Chris Kresser

Is Eating Fish Safe? A Lot Safer Than Not Eating Fish!

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This is going to be a long article and I know not everyone will have time to read it. So I’m going to summarize the key points right up front because I think this information is so important:

Overview

  • Selenium protects against mercury toxicity, and 16 of the 25 highest dietary sources of selenium are ocean fish
  • If a fish contains higher levels of selenium than mercury, it is safe to eat
  • Most species of commonly eaten fish in the U.S. have more selenium than mercury
  • Fish are not significant sources of PCBs and dioxins when compared to meat, dairy or vegetables
  • The benefits of eating fish regularly far outweigh the potential risks, which are negligible
  • Pregnant mothers and young children should eat 2-3 servings of oily ocean fish each week

These days a lot of people are scared to eat fish. They’ve been told that fish are full of contaminants like mercury, PCBs and dioxins that cause neurological problems and may increase the risk of cancer. Pregnant women have been especially warned due to the supposed risk of these toxins to the developing fetus.

In the last few articles I’ve established the importance of the long-chain omega-3 fatty acids EPA and DHA in human health. I’ve argued that the conversion of plant-based omega-3 fats like ALA into the longer chain EPA and DHA is extremely poor in most people.

The conclusion is obvious: fish should be a part of our diet. But is it safe to eat fish?

You might be surprised to learn that the answer is a resounding yes. In this article I’ll demonstrate that concerns about toxins in fish have been overblown, and that there is almost no risk associated with eating fish when a few simple precautions are taken.

The selenium story

Although people are increasingly concerned about the effects of mercury levels in fish, recent evidence suggests that the trace amounts of mercury in the fish Americans eat aren’t high enough to pose a health risk.

But measuring only mercury significantly exaggerates this risk, because it ignores the important role of selenium.

Selenium is plentiful in many ocean fish species, but the public is unaware of its protective role against mercury. Selenium has high binding affinity for mercury. This means that when the two elements are found together, they connect, forming a new substance.

This new substance makes it hard for the body to absorb the mercury separately. Simply put, when selenium binds to mercury, mercury is not longer free to bind to anything else – like brain tissue.

Studies have shown that relevant amounts of selenium (Se) can prevent oxidative brain damage and other adverse effects associated with mercury toxicity. (PDF)

University of North Dakota researcher Nicholas Ralston has published several papers on the protective effects of selenium. He describes the relationship between selenium and mercury as follows:

Think of dietary selenium as if it were your income and dietary mercury as if it were a bill that you need to pay. Just as we all need a certain amount of money to cover living expenses such as food and rent, we all need a certain amount of selenium.

And guess what foods are highest in selenium? You’re right! 16 of the 25 best sources of dietary selenium are ocean fish.

He goes on:

Only one major study has shown negative effects from exposure to mercury from seafood, and that seafood was pilot whale meat. Pilot whale meat is unusual in that it contains more mercury than selenium. When you eat pilot whale meat it’s like getting a bill for $400 and a check for less than $100. If that happens too much, you go bankrupt. On the other hand, if you eat ocean fish, it’s like getting a check in the mail for $500 and getting a bill for $25. The more that happens, the happier you are.

What Ralston is telling us is that as long as the fish we’re eating has more selenium than mercury, there’s nothing to worry about.

Fortunately, studies by several independent organizations have consistently shown that most of the fish we eat contain significantly more selenium than mercury. Fish that contain more mercury than selenium include pilot whale, tarpon, marlin, swordfish and some shark.

The following chart illustrates the relative levels of selenium and mercury in commonly eaten ocean fish:

The selenium health benefit value (SeHBV)

Researchers have proposed a new measure of seafood safety called the Selenium Health Benefit Value (SeHBV) that takes the protective role of selenium into account.

Fish with a positive (above zero) SeHBV ratio would be safe to eat, whereas fish with a negative ratio would be unsafe. Using these criteria, most varieties of ocean fish have positive SeHBV ratios and are thus safe to eat.

A study conducted by the Energy & Environmental Research Center (EERC) and the Environmental Protection Agency (EPA) also found that an estimated 97% of the freshwater fish from lakes and rivers in the western U.S. are safe to eat. It is the only study I’m aware of that has measured both mercury and selenium levels in the tissues of freshwater fish. 1

So how much fish is safe to eat?

The joint recommendation for fish consumption of the EPA and FDA as of 2004 is as follows:

  • Eat up to 12 ounces (2 average meals) a week of a variety of commonly eaten fish and shellfish found consistently low in mercury, including shrimp, canned light tuna, salmon, pollock, and catfish
  • Limit albacore tuna to 6 oz. per week
  • Do not eat shark, swordfish, king mackerel, or tilefish because they contain high levels of mercury

Notice that these recommendations are already quite liberal compared to the fish-phobes who suggest we avoid fish entirely.

But even these recommendations are too strict, because they don’t take the protective effects of selenium into account. As long as the fish is higher in selenium than it is in mercury, there’s no reason to limit consumption to 12 ounces per week.

What about dioxins and PCBs?

PCBs are synthetic organochlorine compounds previously used in industrial and commercial processes. Dioxins are organochlorine by-products of waste incineration, paper bleaching, pesticide production, and production of certain plastics. Yummy!

While it makes perfect sense to try to avoid these toxins to the greatest extent possible, abstaining from fish isn’t a particularly good strategy.

The highest dietary sources of PCBs and dioxins are not fish, but beef, chicken and pork (34%), dairy products (30%) and vegetables (22%). Fish constitute only 9% of our dietary intake of these chemicals.

The primary concern with PCBs and dioxins is cancer. Animal studies and some evidence in humans suggest that both are carcinogenic.

However, an analysis has shown that, per 100,000 individuals, consumption of farmed vs. wild salmon would result in 24 vs. 8 excess cancer deaths, respectively, while consumption of either farmed or wild salmon would result in 7,125 fewer coronary heart disease (CHD) deaths.

Another analysis of the same data suggested that, for all ages evaluated (25-35 to 85 years), CHD benefits outweighed cancer risks by 100- to 370-fold for farmed salmon and by 300- to more than 1000-fold for wild salmon.

It’s important to note that the benefits of fish consumption are based on prospective studies and randomized trials in humans, whereas estimated cancer risks include a 10-fold safety factor and are based on experimental data in animals and limited studies in humans at extremely high doses.

Cancer estimates also assumed lifetime salmon consumption of 1,000 mg/d of EPA & DHA (four 6-oz servings of wild salmon every week for 70 years). Of course virtually nobody in the U.S. currently eats this much salmon.

On the other hand, CHD mortality reduction may be achieved with lower intake (i.e. 250 mg/d – one 6-oz. wild salmon serving per week). At this intake, CHD benefits would be the same (7,125 fewer deaths) while lifetime cancer risk would decrease by 75% (6 and 2 estimated deaths per 100,000 for farmed and wild salmon respectively). The CHD benefits would outweigh cancer risks by more than 3500-fold in the case of wild salmon.

Once again, with few exceptions (the species of fish with more mercury than selenium), it’s not only safe but incredibly beneficial to eat fish regularly.

How beneficial? Let’s find out.

Fish consumption, cardiovascular disease and total mortality

In 2006 Mozaffarian & Rimm published a paper in JAMA called “Fish Intake, Contaminants and Human Health: Evaluating the Risks and Benefits“. They analyzed several studies that examined the impact of fish consumption on both coronary and total mortality. They found that modest fish consumption (e.g. 1-2 servings/wk) – especially of oily fish higher in EPA and DHA – reduced the risk of coronary death by 36% and total mortality by 17%, and may favorably affect other clinical outcomes.

The authors summarized their findings this way:

For major health outcomes among adults, based on the strength of the evidence and the potential magnitudes of effect, the benefits of fish exceed the potential risks.

And:

For women of childbearing age, benefits of modest fish intake, excepting a few selected species, also outweigh risks.

They also pointed out that the Japanese eat 900 mg/d of EPA & DHA on average, and have death rates from coronary heart disease 87% lower than those in Western populations (like the U.S.).

If you’re interested in learning more about this study, I recommend listening to the JAMA Audio in the Room interview with its lead author, Mozaffarian.

Fish consumption, pregnant mothers, and children

DHA is essential for proper development of the brain. It is preferentially incorporated into the rapidly developing brain during gestation and the first two years of infancy, concentrating in the gray matter and retinal membranes.

In a meta-analysis of 14 trials, DHA supplementation improved visual acuity in a dose dependent manner. In another trial of 341 pregnant women, treatment with cod liver oil from week 18 until 3 months postpartum raised mental processing scores at age 4 years.

This is consistent with observational studies showing positive associations between maternal DHA levels or fish intake during pregnancy and behavioral attention scores, visual recognition, memory, and language comprehension in infancy.

An FDA report issued in 2008 noted that the nutrients in fish – especially n-3 LCFAs, selenium, and vitamin D – could boost a child’s IQ by an estimated ten points. 2

The FDA report summarizes evidence suggesting that the greatest benefits to children would result if pregnant women of childbearing age, nursing mothers and young children ate more than the 12 ounces of fish per week currently recommended by the EPA.

According to the National Fisheries Institute, Americans currently consume only five ounces a week of fish high in n-3 LCFA, which is less than half the recommended amount. The NFI also estimates that up to 14 percent of women of childbearing age eat no fish at all, despite the fact that n-3 LCFA are essential to proper fetal brain and eye development.

Based on the new understanding of selenium’s protective role, and the importance of DHA for fetal and early childhood development, pregnant mothers should be advised to eat oily ocean fish regularly.

Fish consumption and autoimmune and inflammatory disease

The first evidence of the significant role of dietary intake of n-3 LCFA in reducing inflammation came from epidemiological observations of the low incidence of autoimmune and inflammatory disorders in a population of Greenland Eskimos compared with gender- and age-matched groups living in Denmark. The Eskimos in this study had dramatically lower rates of psoriasis, asthma and type 1 diabetes, as well as a complete absence of multiple sclerosis.

Animal and human studies suggest that n-3 LCFA suppresses cell mediated immune responses. Increasing the amount of n-3 LCFA while decreasing omega-6 fatty acids leads to improvements and a decrease of steroid use in patients with rheumatoid arthritis and asthma.

This is because omega-3s have been shown to suppress the capacity of monocytes to synthesize interleukin-1 (IL-1) and tumor necrosis factor (TNF). IL-1 and TNF are the principal mediators of mediation in several different inflammatory and autoimmune conditions.

Summary

This is simply a re-cap of the overview presented at the beginning of the article. But it’s worth repeating.

  • Selenium protects against mercury toxicity, and 16 of the 25 highest dietary sources of selenium are ocean fish
  • If a fish contains higher levels of selenium than mercury, it is safe to eat
  • Most species of commonly eaten fish in the U.S. have more selenium than mercury
  • Fish are not significant sources of PCBs and dioxins when compared to meat, dairy or vegetables
  • The benefits of eating fish regularly far outweigh the potential risks, which are neglible
  • Pregnant mothers and young children should eat 2-3 servings of oily ocean fish each week
  1. Energy & Environmental Research Center, University of North Dakota (EERC). EERC Research Finds Mercury Levels in Freshwater and Ocean Fish Not as Harmful as Previously Thought. June 22, 2009. Accessed at http://www.undeerc.org/news/newsitem.aspx?id=343
  2. Energy & Environmental Research Center, University of North Dakota (EERC). EERC Research Finds Mercury Levels in Freshwater and Ocean Fish Not as Harmful as Previously Thought. June 22, 2009. Accessed at http://www.undeerc.org/news/newsitem.aspx?id=343

148 Comments

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  1. why get your omega 3s from fish when you can get it staight from the source- algae! It comepletely removes the risk of the heavy metal consuption, and fish get all the omega 3 they contain from algae, so why comsume the middle guy which has been shown to dramatically reduce sperm count in males, when you can consume omega 3s from the producer, which has no health risks

    • Plus with certain types of algae, some people have issues digesting the cell walls.

      Don’t get me wrong, I love some high quality Spirulina and I also enjoy Chlorella, but it has to be tested for purity and has to be cracked, broken, or split cell wall on the Chlorella.

      I think the Spirulina is easier to digest for most people.
      Spirulina for nutrients, Chlorella for detoxing (the cell wall of Chlorella absorbs a lot of stuff but like anything with osmosis, you can only clean with a sponge for so long before it starts to add more contaminants onto whatever you are cleaning)

  2. Hi Chris, I wonder how true is this today.
    As the years pass, pollution in the water becomes a much bigger risk factor factor. It’s too early to tell how eating fish today will fall in comparison to the past. Overfishing and the rise of the jellyfish are other issues we need to tackle when it comes to eating healthy fish.

  3. Hi Chris,

    which type of fishes can you recommend for daily basis?
    (For example there are a lots of terrify story about pangasius on the internet.)
    Which are the most safest and rich in Omega 3 acids?

    Thank you for everything, I’m reading now your book, listening your podcasts and love them all!!! Thank you soooo much for your work Chris!

  4. Chris, I want to eat more fish for health, I don’t mind mild white fish but have stayed away from the cold water “good” fish due to tast/texture issues. Do you have a recipe that could (Salmon lovers cover your eyes) make salmon not taste like Salmon? I googled it and there are lots of people that don’t like it, but most of the recipes are brown sugar heavy.

  5. Oh, my, if only people knew more about the alternatives to fish! Unless they are eating organically raised products, the amount of garbage they are ingesting is like a horror story!

  6. I have a simple criticism of the selenium protection theory. Pilot whales which are mammals and therefore have much in common with us strictly follow your guidlines eating almost exclusively squid which have one of the lowest concentrations of mercury. Never the less they end up with a mercury level that is double the level of their body selenium. Why wouldnt the same happen to humans?

    • It would not be the same with humans because whales eat squid exclusively and in very large amounts. To rival the consumption a human being would need to eat fish for breakfast, lunch and dinner and let’s face it–how many people do you know that lead this kind of lifestyle?

      • i am worried about fish especially from mediteranean as they have fed on the 1000s of dead human bodi3s that have drowned there

        could someone tell me is this is s afact and id so is the fish sef to eat

  7. Chris you are THE MAN. Thank you for your very concise, pithy articles that cut right through the bull. The warnings that discourage people from eating fish remind me of my dentist, who in his latest newsletter discouraged patients from eating nuts because they might break their teeth (as if it’s better to eat Twinkies!) . . . Anyway, your article hits the nail right on the head. THANK you!

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