Good fish, bad fish: new draft FDA guidance considering mercury exposures

After years of scaring pregnant women away from fishy nutrition, the FDA is finally updating its recommendations to encourage them to eat 8-12  ounces of low-mercury fish a week. That’s 2 or 3 meals per week in order to support fetal growth and development. Curious about what fish are low mercury? Stay away from tilefish from the Gulf of Mexico, swordfish, shark, and king mackerel and limit albacore tuna to 6 ounces a week. Better options include “some of the most commonly eaten fish such as shrimp, pollock, salmon, canned light tuna, tilapia, catfish, and cod”. For locally caught fish, you should check with your local authorities. The new recommendations aren’t final – read the draft and write in if you want more information that would help you make safe and healthy seafood choices. Here’s some things you should consider.

What’s new? 

Fundamentally, the recommendations stress the importance of fish in a health diet, especially for developing brains. It also specifies that it’s tilefish from the Gulf of Mexico that are the problem, not just tilefish generally. The specification to check for local advisories no longer calls out coastal areas as one place you might go fishing. Oh, and there’s a lovely new reminder about thinking about your diet as a whole and how fish fit into your daily calorie and nutrient intake.

Are there remaining unresolved issues? Yes.

For the quantitatively inclined, the draft guidelines include a chart with the omega-3 fatty acid and mercury content in commonly eaten fish. You want more omega-3’s for all that great neurological development and less mercury in your chosen dinner. However, the new guidelines come on the tail of persistent maintenance of the status quo action level for mercury in fish – at 1.0ppm. That’s also known as 29.58 micrograms per ounce, or 118.3 micrograms in the recommended 4 ounce serving. The new draft recommendations use this cutoff to declare the tilefish, swordfish, shark, and king mackerel unhealthy.

However, the EPA and many states use the action level of 0.3 ppm – or 8.87 micrograms per ounce and 35.5 micrograms per 4 ounce serving. Glancing through the new chart, this would also restrict consumption of all types of tuna (not just albacore, as in the recommendation), American lobster, and orange roughy. EPA is also a co-author on the new guidelines, providing an additional level of confusion for those of us who like to go by the numbers, not by the (sometimes dubious) species name of what we’re eating.

The new guidelines also emphasize much more strongly the need to follow local advisories around fish caught in local bodies of water. Personally, I think this should be the main headline of these guidelines. While not all of us are fishing for dinner, someone is catching that fish for you. And in study after study, location turns up as the primary determinant of fish contamination. Seafood traceability is a huge issue in the seafood industry, and unless you buy your seafood straight off the boat (which I highly recommend), it’s very difficult to tell what you’re buying, let alone where it was caught. If you’re in the airshed of a coal-fired power plant or downstream of a farm that historically used mercury-based pesticides,  local fish might turn you into the mad hatter. Same species in another place? Might be fine. There’s few national maps of mercury sources, but the local department of health might have the data for your local trout or shellfish.

What would I add?

The rules about which fish are low in mercury seem lacking in ecological rules-of-thumb. Mercury bioaccumulates up the food chain – meaning, the more steps away a fish is from primary production, the more mercury it will have. It’s generally a factor of ten for each step up the food chain. So shrimp and other herbivores? Unless they’re sitting in sediment made of mercury, it’s fine. Your prize marlin or tuna is a different story – as it ate the fish that ate the fry that ate the shrimp. Also, fish that swim over long distances are less likely to be stuck in one of those watersheds with historic contamination for too long. Whereas that oyster or clam, stuck in its spot in the sediment, will directly reflect the chemistry of its habitat. That’s great for mercury studies, but just something to think about – location matters in your diet, just like real estate.

Just a reminder that guidance from the government on healthy diets is good. And it’s  an evolving story as we learn more about the science of both fish and mercury. So stay tuned, get involved, and find out where your fish comes from before you eat it.