The “Mercury Food Chain” – From the ocean to your baby

Everyone knows that pregnant women should avoid fish and definitely shouldn’t eat raw fish… right? Or at least I thought that was “a given” until I started discussing what my wife and I might eat on our next date in the big smoke. Well, it turned out that we were to have sushi and that I had no say in the matter.

There is no better topic than pregnancy for old wives tales to prevail and the list of different foods that you can and can’t eat seems to be not only the longest, but the most contentious when it comes to the cross-border battle of who’s “common sense” was to prevail. While it is hard to prove most wives tales either right or wrong, but I assumed that something as important as food must have a “right” answer.

This is the fifth installment in a series about my personal experience of being pregnant in Japan. Although I hope that the observations have value for gaijin of both sexes, I’m intentionally writing this series from my own perspective – a Gaijin Father / Japanese Mother. (You might like to read the first, second, third, and fourth installments before reading on. And sorry to those expecting Father’s who were wondering what had happened to the series – you’ll know what caused the sudden blackout for me, right after your child is born!)

As I mentioned in part part two, my wife and I have tried to do our research about pregnancy in both English and Japanese in order to avoid bias toward one culture versus the other. Perhaps the biggest contradiction I noticed between the two banks of knowledge was how fish is treated. While every English book (and website) has numerous warnings peppered across at least 2-3 different chapters of the book telling you that you must reduce your intake of oily fish (example), Japanese books as a rule actively encourage pregnant Mum’s to eat as much fish as they can. To make matters worse, neither side of the debate writes anything that isn’t true. It’s just that the rationale employed by each culture is so different, that a Martian would be forgiven for thinking that perhaps they were referring to entirely different species.

So how can there not be misinformation if both sides are arguing opposing points, you ask? Rather than lying, it seems that most authors take the approach that “simple is best” and (almost always) fails to mention some key facts about fish/seafood when describing what it’s readers should unilaterally do. The typical English book talks about the high mercury levels found in many fish, especially tuna, which can affect the neural development of your fetus severely if ingested in excess. On the other hand, Japanese books focus on the healthy properties of fish, especially blue fish and recommend that you should eat fish regularly in order to increase your intake of DHA and other Omega 3 & 6 fatty acids. In reality – although contradictory – they are both correct.

So that brings me to my next question. Why don’t we ever hear both sides of the story? I guess in the English books, authors are just leaning on the conservative side and recommending against something that isn’t easy to measure. Who wants to take the risk of being sued by a pregnant Mother who misinterpreted your recommendations? Surely there is a limit to how far they should be allowed to play on our fear though? On the other hand, it’s no surprise that the Japanese, who are amongst the longest living, biggest consumers of fish in the world aren’t too worried about the side-effects of over consumption of fish. Or are they? Well it turns out that the Japanese government is (good on ‘em!). Even though it is rarely mentioned in Japanese books about pregnancy, the MHLW (厚生労働省) actually announced recommendations for pregnant women to reduce their intake of various types fish for fear of mercury poisoning. How many times have you been shocked to hear from well educated Japanese friends that they had no idea that tuna consumption could be unsafe for their unborn baby?

It boils down to the fact that too many books on pregnancy in Japanese are designed to sell. They are supposed to be fun, easy to read and almost always “edited” by a magazine publisher as opposed to being “authored” by a medical professional. Given that being a pregnant mother in Japan is stressful enough with your hubby doing overtime until the middle of the night, the last thing a pregnant Mum wants is to read that she can’t even eat fish. Half of the mags out there will focus pages upon pages on fish recipes.

It’s worth showing your Japanese spouse the MHLW’s “水銀を含有する魚介類等の摂食に関する注意事項” (Translation: Warning on Intake of Seafood Containing Mercury) as she probably won’t discover it herself unless she is reading a University level textbook on nutrition. It was announced first in 2003 and updated again at the end of 2005 to double the number of fish that could potentially have high levels of ethyl-mercury. The ministry regularly updates their official site and has a pretty good FAQ about the guidelines titled:魚介類等に含まれる水銀について (Translation: Memo on Mercury Levels in Seafood). Their most recent effort in publicizing the guidelines is in this PDF called 「これからママになるあなたへ　お魚について知っておいてほしいこと」 (Translation: A message for all expectant mothers – A few things you must know about fish (found on MHLW’s page here).

Before I go into the details, you’ve got to forgive me for reproducing the first paragraph here:

魚介類（クジラ、イルカを含む）は、良質なたんぱく質や、血管障害の予防やアレルギー反応を抑制する作用があるDHA(ドコサヘキサエン酸)、EPA(エイコサペンタエン酸)を多く含み、またカルシウムなど栄養素の摂取源で、健康的な食生活を営む上で重要な食材です。
Translation: Seafood (including whales and dolphins) is a good source of good protein, DHA (which is known to reduce allergies and vascular damage) and EPA. It is rich in calcium and other nutrients and so is an essential item of any healthy lifestyle.

Sure. I hear you. What is written is totally correct and English books should remind their readers about it more often. But did they really have to make that reference to whales and dolphins in the very first sentence? Anyway, after that strong fish advocating opening, the document goes on to recommend a reduced intake of various fish during pregnancy. It’s worth scanning the list below as the kind of fish you see in a Japanese supermarket are totally different to what you’ll see in other parts of the world. The biggest drawback of ordering an English book on amazon.com is that all of its examples will be about fish that you find in US supermarkets. I’m pretty sure you’ll agree that there are at least a few items on the Japanese list that aren’t on the US list and vice-versa:

The bigger the Tuna are, the more likely they are to have high mercury
levels in their fat (Photo: Tsukiji Fish Market, Tokyo Japan)

Not more than two 80g servings per week:

• キダイ (Yellowback Sea Bream)
• マカジキ (Striped Marlin)
• ユメカサゴ (Rockfish)
• ミナミマグロ（インドマグロ） (Southern Bluefin Tuna)
• ヨシキリザメ (Blue Shark)
• イシイルカ (Dall’s Porpoise)

Not more than one 80g serving per week while pregnant:

• キンメダイ (Splendid Alfonsino)
• ツチクジラ (Baird’s Beaked Whale)
• メカジキ (Swordfish)
• クロマグロ(本マグロ） (Bluefin Tuna)
• メバチ（メバチマグロ） (Bigeye Tuna)
• エッチュウバイガイ (Finely-striate Buccinum) – better known as 白梅貝（シロバイガイ)
• マッコウクジラ (Sperm Whale)

Not more than one 80g serving per fortnight:

• コビレゴンドウ (Short Finned Pilot Whale)

Not more than one 80g serving every two months:

• バンドウイルカ (Bottlenose Dolphin)

Large side of Tuna showing the oily toro underbelly
(lighter colour, on right) – Tuna was not included
in the original guidelines for pregnant women, but
was added later on

Interestingly, when the first version of these guidelines were released back in 2003, the list was only half as long and didn’t refer to any kinds of Tuna. As the general rule of thumb, in the West people are encouraged not to eat large pelagic fish like tuna, shark and swordfish. I guess the new Japanese list is matches reasonably well with Western recommendations, but I would love to hear the real story as to why tuna wasn’t in the original version, and how it came to be included). As the focus on this article is on health and pregnancy in Japan, please direct any comments about Whale and Dolphin eating to our dedicated thread here. For or against whaling, the Japanese guidelines are a fascinating look into Japanese society when you consider that the MHLW have actually gone out of their way to point out that Minke Whales (the ones that the Japanese do the most “research” on) are safe to eat during pregnancy as they have low ethyl-mercury levels. (You can see the government list of official mercury levels by fish here for more details).

While I’m at it, let me briefly list the other risks that most tin foil hat wearing English books (and no Japanese books) will have you worrying about every time you see fish on your wife’s plate. Most of the references to poisoning will at the very least lead to gastroenteritis which is dangerous as it can cause dehydration from vomiting and diarrhea (Source: “What to Eat When You’re Expecting”).

● Some fish caught in lakes and rivers are high in Dioxins and PCBs (e.g. blue fish, lake trout). This, once again, seems to be a US-specific issue based on research into US lakes and rivers. I don’t know enough about Japanese estuaries, but if you happen to live near either Yokkaichi (四日市) or Minamata (水俣), I’d probably avoid as much of the local catch as possible as a precaution.

● Raw shellfish (if contaminated) can cause hepatitis-A, cholera or gastroenteritis.

● Some fish found in warm tropical waters (eg. Sea Bass, Grouper (yum!) and Red Snapper) can be a cause of Ciguatera poisoning. The risk is particularly high when there is a “red tide” (a rapid increase in the amount of blooming algae in the Ocean). (more details). Don’t think that just because you live in Japan that this isn’t related. Because Japan imports a lot of its fish, it’s worth trying to find out where your fish was caught.

● If you don’t refrigerate (or freeze) your fish immediately after catching it, normal bacteria can create large amounts of a toxin that will cause Scombroid poisoning. Tuna and Mahi-Mahi are two examples of common culprits.

● If I haven’t written enough to make you totally paranoid… While we’re on the topic: raw meat (especially pork, lamb and venison) may contain “Toxoplasma Gondii” which can blind the fetus or damage its nervous system and may cause schizophrenia (more details). And soft cheeses may have Listeria and raw eggs might have salmonella. (This must be the record for the most Wikipedia links in one paragraph!)

A lot of these worries center around the consumption of raw seafood. Japanese pregnant women have been eating raw fish for centuries without any problems (Just like you’d never hear a Doctor in Thailand or India advising pregnant mothers not to eat spicy foods!). Why? I can think of at least two good reasons. (1) They’re used to it. Anything that you eat on a regular basis, is unlikely to be a shock to your system if you consume it while you’re pregnant. Perhaps more importantly, (2) the Japanese food distribution network is designed specifically to cater for raw fish. Because there isn’t that much consumption of raw fish in the West, fish are generally treated more roughly by supermarkets and distributors.

Whale on Sale – Most whale and dolphin meat contain high
levels of Mercury (Photo: Tsukiji Fish Market, Tokyo Japan
Note the “whales of the world” poster in the background)

At the end of the day, if the customer is going to deep fry the fish then who really cares how long it has been sitting out, thawing under the sun. You’d never get away with that at a supermarket in Japan. In fact eggs are a great example. Have you ever compared the length of egg used by dates in Japan with those in the West? Eggs in the West are generally “good for consumption” for at least one month longer than Japanese eggs. Why? Because a lot of Japanese eggs will be eaten raw and supermarkets can’t take the risk of salmonella and other creepies having their way. If you have any friends in the Japanese supermarket trade, it is a very interesting dinner conversation topic to ask them about how they treat their eggs (compared to say Walmart in the West).

To be very clear, if your wife is Japanese and living in the West, you should definitely discourage her from eating raw fish, eggs, meat etc while she is pregnant as the quality just isn’t the same as back home. But if you’re living in Japan, then you are probably doing your unborn baby a disservice by not eating fish. If you take the Western approach of not eating any fish because its all too complicated and overwhelming then you miss out on a valuable source of DHA which in recent studies has been linked with a lower rate of premature births (source: “Your Pregnancy Week by Week”). Common Japanese fish like Sardines (イワシ)、Mackerel (サバ)、Herring (ニシン)、Salmon (サケ)、Pacific Saury (サンマ) are all good sources. Omega-3 fatty acids are thought to promote neural development and so are particularly important in the 2nd and 3rd trimesters when the brain is growing at its fastest. (By the way, the best vegetarian source of Omega-3 fatty acids is from flax seed (linseed). We used flax seed oil in our cooking and ate eggs from hens which were fed flax seed. They’re pretty hard to find but available in some large International Supermarkets). Perhaps, even more important for Gaijin Daddy’s out there, recent research suggests that a high DHA intake can help reduce the chance of post-partum depression (reference) so make sure you keep eating fish after bubs joins you at thedinner table too!

Pregnant women (and their paranoid husbands) should be presented with both sides of the story and given enough information to chose themselves. Unfortunately there are very few books or websites that do so (in either language). The best that I have found so far is the Environmental Defense Fund. Make sure you download their pocket seafood selector (here) which has a brilliant chart that tells you which fish are high in fatty acids, which are likely to be high in mercury, and hence which are the most sensible items for your dinner table. Print out a copy and keep it in your wallet so you have it handy when you go shopping. Good luck!