We land-based creatures have been eating fish for tens of thousands of years. It’s a readily available source of high-quality protein and, when done right – say with a dash of sea salt, pepper, lemon and a little butter or ghee – makes a delicious addition to any plate.

‍

But there are important factors to keep in mind when it comes to the type of fish you consume. While over-fishing and industrial fish farming are concerns on a macro ecological scale, closer to home, fish-lovers need to be careful about not elevating their body’s mercury levels – a common problem that often comes with ‘too much of a good thing.’

‍

While not over-doing it is a good rule of thumb for just about any kind of fish you enjoy, it’s especially important when it comes to tuna, one of the most popular lunch and dinner staples in the fish-eating world, which despite its many upsides, can be very high in mercury. So how to minimize the downsides and take advantage of tuna’s pluses? Here are a few thoughts on how to do tuna right:

Who can forget mom’s tuna sandwiches?

When I was growing up, a tuna salad sandwich in my lunchbox was my favorite, and a welcome break from peanut butter or baloney, both of which featured perhaps a bit too prominently in my school lunch-time rotation – and were a lot harder to trade up for something tastier. I (and my lunch buddies) could have eaten tuna every day, but somehow my mom must have known better. Since then, we’ve all been made aware that one of the primary concerns with tuna consumption is mercury. 

Why is tuna higher in mercury than so many other fish?

It’s a bit of a high-on-the-food-chain problem: Tuna is a large, predatory, fish (averaging about 150 pounds though some can grow to 900 pounds or more) with a long lifespan (for a fish, that is, averaging 25 years or more). So, there’s plenty of time for their bodies to accumulate mercury. Some of it comes from the waters they live in, with some mercury occurring naturally while literally tons more washes in from the atmosphere and industrial runoff, thanks to man-made mercury emissions, like burning fossil fuels and mining operations. A large percentage of that mercury, however, comes from the smaller fish the tuna consumes. The smaller fish pick up mercury from the tiny marine animals they feed on, which have also absorbed mercury from their less-than-pristine aquatic homes.

But wait — tuna’s full of good stuff too.

The good news is you probably don’t have to tune tuna out entirely, nor should you -- you’re also getting a lot of nutrients your body needs. What’s tuna got to offer? In addition to versatility, affordability and convenience, a few of tuna’s upsides include:

1. Protein, and plenty of it: Tuna is a great source of high-quality protein, needed for building and repairing tissues in the body. Just one serving can provide up to 25 grams of protein, making it an excellent choice for athletes and active folks, and those wishing to build or hold onto muscle.
2. A nice dose of omega-3 fatty acids: One of tuna's standout upsides is its high concentration of omega-3 fatty acids, which are known to support brain health, help tame inflammation, and lower the risk of heart disease. Regular consumption of omega-3-rich foods like tuna can also improve cholesterol levels by increasing "good" HDL cholesterol and reducing "bad" LDL cholesterol.
3. A powerful nutrient punch: Plentiful amounts of key vitamins and minerals are always a good thing to have on your plate and tuna’s got many of the biggies, including:

• Vitamin D: Supports bone health and immune function.
• Vitamin B12: Crucial for nerve function and the production of red blood cells.
• Selenium: A potent antioxidant that protects cells from damage.
• Potassium: Helps maintain healthy blood pressure and electrolyte balance.

Mercury levels impact the body and brain. 

According to The New York Times, on average, Americans eat about two pounds of tuna annually, a good bit more than any other seafood except for shrimp and salmon. By now though, most habitual fish-eaters know that while there is mercury in most (if not all) species, eating smaller, shorter-lived, lower-down-the-food chain-fish, a.k.a. those with less mercury ‘bioaccumulation,’ is one way to keep mercury levels in check. However, for hard core tuna-lovers or for those whose idea of seafood is a steady diet of canned tuna (you know who you are), mercury contamination becomes a more significant concern, particularly if you’re lunching on tuna sandwiches 3+ days a week.

‍

Trouble is, mercury is a heavy metal, a known neurotoxin and it’s hard to know how much you’re taking in – as mercury levels vary from species to species, and in canned tuna levels can even vary from can to can. After tuna is eaten and absorbed, mercury can be deposited in various organs such as the kidneys and brain. The body will naturally eliminate mercury over time through urine and stool, but if an excessive amount builds up, it can cause permanent damage to the kidneys, nervous system, and brain. In short, too much mercury in your system is bad news from head to toe.

OK, so what about the kids?

Got kids? Or about to have one? Mercury isn’t ideal for the younger set either. Keeping their still-growing bodies, and developing brains and nervous systems in mind, use a light touch – think small portions, and depending on their age, make it no more than once or twice weekly. For pregnant people, here too, less is more. Protecting developing brains means exercising even more caution. Some research goes so far as to recommend pregnant and nursing people avoid tuna altogether, opting instead for smaller, lower-in-mercury fish, like sardines or anchovies and getting your omega-3s from other dietary sources, like flax seeds, chia seeds, walnuts and omega 3-enriched  eggs. For detailed recommendations for children ages from 1 -11 years old and pregnant people, click here to view the FDA’s current fish consumption guidelines.

When levels get too high, you’ll very likely feel it.

How to know if your mercury levels have crept up too high? With too much mercury comes a number of symptoms to keep an eye out for, like disrupted sleep, movement disorders, memory issues and cognitive decline as well as depression, behavioral problems, vision loss, headaches and tingling/numbness of the limbs, just to name a few. Uncomfortable and unpleasant for sure, but more concerning though is that neurotoxicity is a significant factor in development of progressive neurological disorders such as Alzheimer’s disease, Parkinson’s and multiple sclerosis. 

So, how are your levels?

It helps to know where your baseline is. Depending on things like your diet, stress levels, how much you weigh, genetic susceptibility, etc., you may not be bothered by mercury at all, or you may experience debilitating symptoms after eating a relatively small amount, or maybe you fall somewhere in between. But no matter where you fall on the spectrum, I recommend regular fish eaters – and especially tuna fans – get their mercury levels checked periodically. 

‍

In my practice, we measure these levels in our regular workups so we can get a better understanding of how much tuna a patient can safely eat. We also do a genetic test which measures the “glutathione-S-transferase” (GSTM1) gene. If a patient is missing a copy of the GSTM1 gene, that missing copy is associated with increased susceptibility to mercury toxicity. So, when we find a GSTM1 ‘deletion’, we’ll add a supplement of sulforaphane to increase the production of enzymes that help the body excrete toxic substances like mercury. 

‍

For those patients whose mercury levels aren’t severe but do come in just a little higher than we’d like, we’ll recommend avoiding large fish like tuna and swordfish for a full 3 months. And, for those with more significantly elevated mercury levels, we’ll often recommend oral chelation therapy to aid removal of the excess.

Five tips for managing tuna consumption with care.

Eating tuna, or for that matter, any fish in the sea has both pluses and minuses, but in general, the thinking is that the potential brain benefits outweigh the downsides, so the key is moderation, remaining conscious of what kind of tuna’s on your plate and how much of it you eat each week. How to manage your consumption wisely? Here are a few tips:

‍

1. Think of tuna as a treat – as in, not an everyday default. If you’re a healthy adult, tuna once or twice a week is plenty, particularly if you’re also eating an additional serving of lower mercury fish during the week.

‍

2. When it comes to canned tuna, your lowest-risk choice is going to be skipjack. Pass on albacore. Tasty as it may be, albacore tends to pack loads more mercury, in some cases upwards of three times as much according to a recent Consumer Reports research on tuna safety. ‘Light’ tuna’s not a great choice either as the cans (or pouches) will likely contain a mix of albacore, and other higher-in-mercury tuna species. Pregnant or nursing? Consider taking a pass on tuna altogether for the time being.    

3. When buying fish at the market, to keep mercury levels as low as possible, try to avoid species like bluefin and bigeye which tend to score high on the mercury meter. Yellowfin will usually have less mercury than bluefin or big eye, but more than skipjack, so if you’re hankering for a tuna steak dinner, try to keep your yellowfin portion size on the conservative side, just 3 or 4 oz per serving, no more than once a week. 

‍

4. Buy the good stuff – as in tuna that’s sustainably fished, using the one-at-a-time, pole or line-caught methods. Though it will be more expensive, this method is far kinder to the environment, versus ecologically-damaging, net methods which scoop up everything in their path, wreaking havoc on delicate marine ecosystems. This important distinction will be listed on the can’s label – and if it’s not, then leave it on the shelf.

‍

5. Another canned tuna tip: The Montererey Bay Aquarium (MBA) recommends looking for ‘free school’ or ‘school caught’ designations on canned tuna labels as well. This indicates that the fisheries have measures in place to catch just tuna, and not any random creatures that happen to be swimming by. For a deeper dive on tuna and hundreds of other fish in the sea, the MBA publishes a highly-respected, well-researched sustainability-focused seafood guide with more tips and valuable information for fish-lovers everywhere.