Seafood products are often lauded for their omega-3 content, which can support all kinds of health goals. But what exactly are omega-3s, and how do you balance the nutritional components of certain types of seafood with known toxins like mercury?
Here, we’ll take a close look at specific seafood options to see which ones offer you the most benefits and the least risk.
Fatty acids are building blocks for fat, which is essential for our bodies’ continued survival. There are multiple fatty acids, including several under the omega-3 umbrella. In seafood, you can find two major omega-3s: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). A third common omega-3, alpha-linolenic acid (ALA), resides in plant oils you find in certain nuts and seeds.¹ And other omega-3s, such as docosapentaenoic acid (DPA), are becoming more interesting as we learn about them.
ALA is the only omega-3 that’s an essential fatty acid, which means your body can’t make it on its own. Your body can break ALA down into EPA and DHA, but not in sufficient amounts compared to what you can get from seafood.²
Omega-6 and omega-9 fatty acids also play important roles in our health. Omega-6s even play a crucial part in your body’s utilization of omega-3s. But, unlike omega-3s, certain omega-6s may actually promote inflammation.¹¹ ¹³ Studies show that the average omega ratio is 20-50:1 omega-6s to omega-3s. To reduce the risks from overconsumption of omega-6s, researchers recommend people consume polyunsaturated fatty acids in a 4-5:1 (omega-6s to omega-3s) ratio instead.¹⁴ Basically, the average person should consider reducing their omega-6 intake and potentially increasing their omega-3 to achieve the proper ratio.
Some studies have shown that omega-9s reduced inflammation and prevented increases in plasma corticosterone (also known as cortisol, a stress hormone) in mice.¹⁵ One type of omega-9, oleic acid, is the primary type of fatty acid found in olive oil. Researchers note that the generous use of olive oil (and, by extension, oleic acid) in the Mediterranean diet might play a role in why it’s associated with lower death rates from vascular diseases and cancer.¹⁵
The essential fatty acids are alpha-linolenic acid (omega-3) and linoleic acid (omega-6).¹⁶ Essential fatty acid deficiency (EFAD) is rarely seen in healthy adults and children who eat a varied diet.¹⁷ Some populations, such as those with cystic fibrosis or gastrointestinal diseases (including, but not limited to, Crohn’s disease, ulcerative colitis, and celiac disease), are at increased risk of EFAD.¹⁷
Researchers find that most EFAD reports are due to omega-6 deficiency, while the fewest complaints arise from a lack of omega-3s.¹⁷ You can also become deficient in nonessential oleic acid (omega-9), but your body would need to metabolize its stores of omega-3s and omega-6s first, in that order.¹⁶ ¹⁷
Some of the physical signs of EFAD include:¹⁷
Omega-3 fatty acids boast various health benefits that are widely studied and agreed upon among much of the scientific community. They include benefits such as:
The heart health benefits that omega-3s offer are particularly impressive. One meta-analysis of 14 clinical studies — each of which boasted over 1,000 participants — showed decreases in major adverse cardiac events and myocardial infarction.³
There’s currently no established upper limit of omega-3s and no evidence showing that omega-3s from food can cause adverse effects.²² When people do experience side effects, it’s generally due to supplementation. Most experts agree that supplement doses shouldn’t exceed 5,000mg (5g) per day; it’s best to stick to this limit to reduce your chances of side effects. If any negative effects do arise, they’re generally mild and may include:²² ²³
These side effects usually occur only when individuals chronically consume more than 5g per day of omega-3s — the equivalent of about nine ounces of king salmon daily. If you get most of your omega-3s from seafood, you may need to be more concerned about mercury than anything else, depending on the type of fish.
Generally speaking, mercury concentrations in seafood increase as you move up the food chain. That typically means that larger fish contain more mercury than smaller fish. However, the same is not true of omega-3s. A better indicator of omega-3 concentration than size is the darkness of a fish’s flesh (not the scales, but what’s underneath). That means fish like salmon, herring, mackerel, and bluefish will have significantly more fat content than fish like cod, pollock, or flounder. And a large portion of that fat content is omega-3 fatty acids.
Here’s a look at the kinds of seafood with the highest omega-3 content (based on a serving of 100g — about 0.2lbs — of raw fish) and their corresponding mercury levels. The data in the following tables comes from the USDA’s FoodData Central database and the FDA’s data on mercury levels in commercial fish from 1990-2012.²⁴ ²⁵ When determining low to high on the mercury scale, we referenced the FDA’s guidelines stating the following:²⁶
|>1,500mg Omega-3||1,000-1,500mg Omega-3||Mercury level|
|Salmon, farmed (Atlantic)||Low|
|Salmon, canned (Pink, Sockeye & Chum)||Low|
|Mackerel (Pacific & Jack)||Low|
|Mackerel, canned (Jack)||N/A|
|Tuna, fresh (Bluefin)||Med/High|
These kinds of seafood have far fewer omega-3s in them. However, the ones with low levels of mercury are still safe to eat as great sources of healthy fat and lean protein.²⁴ ²⁵
|200mg Omega-3||200-500mg Omega-3||Mercury level|
|Scallops, mixed species||Low|
|Tuna, fresh (Yellowfin)||Med/High|
|Surimi Product (Imitation Crab)||N/A|
|Tuna, Canned (Light, Water, No salt)||Low|
|Clams, mixed species||Low|
|Flounder or Sole||Low|
|Halibut (Pacific & Atlantic)||Med|
|Ocean Perch (Atlantic)||Low|
|Squid, mixed species||Low|
While the FDA’s advice on the best fish choices is intended for those more vulnerable to adverse effects from mercury — children ages 1-11 and adults who may become pregnant, are pregnant, or are breastfeeding — the recommendations align with the Dietary Guidelines for Americans.¹² You can safely abide by them even if you aren’t part of a vulnerable population.
The FDA advises that, based on mercury levels, you can eat 2-3 servings of fish from the best choices list or one serving from the good choices list per week. A serving means a different portion depending on the person’s age. The FDA recommends the following serving sizes:¹²
Below are 20 of the FDA’s best fish choices (2-3 servings weekly). You can find the complete list of fish in each category on the FDA’s advice page.¹²
Next are 20 fish that the FDA considers to be good choices (limit to one serving per week):¹²
And finally is the list of seven fish with the highest mercury levels that the FDA recommends you avoid:¹²
In addition to these guidelines, the EPA has even more resources you can use to navigate healthy seafood options, including a database of state, territory, and tribe fish advisory contacts.
It’s also important to note that not only can fish itself become tainted with heavy metals, but omega or fish oil supplements also run the risk of contamination.¹⁹ ²⁰ Overall, though, as long as you generally stick to fish from the FDA’s best choices list or supplements from a trusted source, mercury consumption shouldn’t be a concern.²¹ If you’re curious about some good supplement options, we’ve put together a couple of guides on the best fish oil and best krill oil supplements.
Even if you realize you need to eat more fish to increase your omega-3 intake and balance out your omega-6 to omega-3 ratio, one potential hangup is sustainability. Some fisheries create significant environmental impacts — from trawling behaviors that can destroy reefs, catching and killing unintended species, to the industry’s carbon footprint as a whole.
Fortunately, there are a few sources you can rely on for up-to-date information about which kinds of seafood and areas of production offer the most sustainability and support for the continued health of our oceans.
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