Potentially one of the most health promoting foods on the planet, seafood unfortunately has a bit of a stormy reputation. Nearly everything from the sea is a life promoting food and should be an integral part of everyone’s regular food consumption.
However, due to mass farming and contamination people are often not comfortable eating fish. Farmed fish are something to be scared of, that I have no doubt of. Wild caught seafood should always be a goal. But often the biggest concern regarding seafood is mercury. A toxic metal, we have been conditioned to be almost paralyzed by the fear of mercury. Scared to the point where many people will abstain from eating fish and seafood simply due to the fear that consuming toxic, mercury-laden sea creatures would outweigh any health benefit.
Are our fears about mercury slightly misguided? It might appear so. Why? Mercury is toxic, that much is pretty clear. How toxic it is in the context of fish is another story. Fish and seafood do have mercury in them, more so now than ever before. Here’s the catch: the mercury toxicity of fish depends heavily on the levels of selenium in the fish and the rest of the diet. Mercury has a high affinity for binding to selenium (a potent enzymatic/antioxidant precursor) meaning, if the selenium content of a fish exceeds the level of mercury, there is plenty free selenium to subdue any threats or oxidation in the body. If mercury is higher than selenium, some mercury will bind to the selenium, rendering it inert but the rest will be left free creating a toxic situation.
Thankfully, a simple ratio can be calculated between the two compounds and we can now look at a food’s Selenium Health Benefit Value (SeHBV) to assess the mercury risk. Higher selenium to mercury ratio comes across as a positive score (.52) and higher mercury to selenium content is represented as a negative score (-.37). Greater positive scores are better and greater negative are worse. Additionally, if a person’s diet is high in selenium the threat of mercury is even less of an issue.
The good thing is that nearly all ocean seafood has equal or higher amounts of selenium, meaning mercury is a non issue for most fish. As a general rule, the higher on the food chain a fish is, the more likely it has a higher mercury to selenium ratio. Therefore, bigger, predatory species like pilot whale, swordfish, shark, king mackeral, tilefish and larger tuna are some of the only species we might consume with a positive mercury balance. Nearly every other fish has a positive selenium ratio. Mahimahi, albacore, yellowfin and opah are among many of the widely consumed fish that are selenium positive.
Here’s an infographic I came across when reading Chris Kresser’s article on the same subject, which goes into much more detail:
As you can see, as a general rule, ocean fish are typically higher in selenium than mercury.
So what’s the Bare 5 Bottom Line on seafood?
1. Seafood is a tremendous nutrient dense food.
2. Don’t be scared of seafood, be smart.
3. Mercury is only a concern in a few larger predatory fish.
4. If selenium is greater than mercury, the fish is safe to eat.
5. Pros of eating seafood outweigh the cons in nearly every case.
Thanks for reading, have a great fish filled week!
P.S. Fish Info & Safety Documentary
Vital Choice is one of my favorite resources for high quality, sustainable seafood.