While flounder is a popular and commonly consumed fish, there is little scientific research specific to it.
However, based on its nutritional provision, here are some of the potential health benefits flounder may provide.
Omega-3 Content and Heart Health
Flounder isn’t as rich in omega-3 as some oily fish species, but it does have a moderate omega-3 content. Each 127-gram cooked serving of flounder provides0.38 grams of EPA and DHA (0.21g of EPA and 0.17g of DHA).
EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are highly bioavailable omega-3 fatty acids. While there is no official recommended intake for them the Dietary Guidelines for Americans 2020-2025 encourage “seafood choices higher in EPA and DHA.”
Additionally, the American Heart Association recommended two servings of fish per week, adding “particularly fatty fish”
Scientific research suggests that omega-3 may help to lower cardiovascular risk and improve outcomes. For example, a 2023 study found that an omega-3 index in the 8-11% target range is associated with a lower risk of cardiovascular events and lower all-cause mortality.
The omega-3 index refers to the total amount of EPA and DHA in the blood.
A 2021 systematic review and meta-analysis of 38 randomized controlled trials, involving 149,051 participants, also found potential benefits from increased EPA and DHA intake, associating omega-3 supplementation with a:
7% reduced risk of cardiovascular mortality
9% reduced risk of coronary heart disease events
5% lower risk of major adverse cardiovascular events
Flounder is not an oily fish, and it is far from being the most significant dietary source of EPA and DHA. However, with a typical 0.38 grams of EPA and DHA per 127g serving, flounder can still make a reasonably good contribution to omega-3 intake.
May Benefit Cognitive Health
There is also some evidence that omega-3 intake may have cognitive health benefits.
In this regard, a 2022 systematic review of nine randomized controlled trials investigated the effect of omega-3 on brain function.
The review found that omega-3 improved cognitive well-being, with demonstrated improvements in learning ability and memory-based tasks.
However, we should note that the trials included in this review used approximately 1.0–2.5 grams of omega-3 per day.
Since flounder provides 0.45 grams of omega-3 (including 0.38g of EPA and DHA) per 127g fillet, this would be equivalent to 283–706 grams of flounder per day.
This highlights that although flounder can contribute omega-3 to the diet, it is not among the best sources.
Bone and Immune Health
As a source of vitamin D, flounder may help contribute to bone and immune health.
Aside from foods fortified with vitamin D, there are not many natural dietary sources of this essential vitamin. However, fish is one food group that does provide it.
A 127-gram serving cooked flounder has 4.44 mcg of vitamin D, which is equal to 22% of the daily value.
Among its numerous functions, vitamin D is essential for supporting the immune system and maintaining strong bones.
However, once again, it is worth noting that oily fish provides more vitamin D than leaner fish like flounder. This is because vitamin D is a fat-soluble vitamin, primarily found in fat stores.
Flounder Is a Lean Protein
While oily fish offer more benefits than flounder for omega-3 and fat-soluble protein, they can’t compete for protein density.
Since flounder only contains a small amount of dietary fat, it is among the leanest protein source, with a cooked 127-gram fillet providing 19.3 grams of protein for only 109 calories.
To demonstrate this protein-density for you, here’s a quick comparison:
127g cooked flounder: 19.3 grams of protein for 109 calories
In other words, flounder is a great option for anyone wanting to consume more protein without adding too many extra calories.
Some other lean, protein-rich fish options include haddock and branzino.
A Rich Source of Selenium, Which Plays a Role in Immune Health
Selenium is another essential nutrient that flounder contains in significant concentrations. A 127-gram cooked flounder fillet has 41.4 mcg of selenium, which is 75% of the recommended daily value.
Additionally, a 2021 systematic review and meta-analysis reviewed the impact of selenium status on cardiovascular disease. This review demonstrated that high selenium levels in the body compared to low were associated with a 31% lower risk of cardiovascular mortality.
Adding a fillet of flounder to the weekly diet is a simple way to significantly increase selenium intake.
Nutritional Profile
Let’s start by looking at the full nutritional values of flounder.
The following tables show the complete nutritional values of cooked flounder per 127-gram fillet.
Table 1: Typical calorie and macronutrient content of cooked flounder per 127-gram fillet
Flounder is a protein-packed fish that is low in calories and provides a small to moderate amount of omega-3.
Vitamins
Vitamin
Amount
% Daily Value
Vitamin A (RAE)
15.2 mcg
2%
Vitamin C
0 mg
0%
Vitamin D
4.44 mcg
22%
Vitamin E
0.98 mg
7%
Vitamin K
0.1 mcg
<1%
Vitamin K2 (as MK-4)
0.38 mcg
—
Thiamin (B1)
0.03 mg
3%
Riboflavin (B2)
0.03 mg
2%
Niacin (B3)
1.63 mg
10%
Pantothenic acid (B5)
0.29 mg
6%
Vitamin B6
0.15 mg
9%
Folate (B9)
7.62 mg
2%
Vitamin B12
1.66 mcg
69%
Choline
101.47 mg
18%
Table 2: Typical vitamin content of cooked flounder per 127-gram fillet
As the table shows, a typical serving of flounder provides high amounts of vitamin D and B12. It is also a good source of niacin, vitamin B6, and choline.
The fish contains high amounts of vitamin B12, vitamin D, niacin, and vitamin B6.
Minerals
Mineral
Amount
% Daily Value
Calcium
31.8 mg
2%
Iron
0.29 mg
2%
Magnesium
27.9 mg
7%
Phosphorus
392 mg
31%
Potassium
250 mg
5%
Sodium
461 mg
20%
Zinc
0.50 mg
5%
Copper
0.03 mg
3%
Manganese
0.02 mg
1%
Selenium
41.4 mcg
75%
Table 3: Typical mineral content of cooked flounder per 127-gram fillet
Among its broad mineral profile, flounder contains high levels of selenium and phosphorus.
From the table, you’ll also notice that it has a relatively high provision of sodium at 461 mg per 127g fillet. It is worth noting that this amount of sodium is not naturally present in flounder, and the USDA source data is likely for flounder cooked with additional salt for seasoning.
Potential Drawbacks
As with any food, there are also some rare potential drawbacks to consider about flounder.
Fish Allergy
While not as prevalent as shellfish allergy, finfish allergy is a condition estimated to impact 1% of the United States population.
So in relatively rare cases, flounder may cause an allergic reaction in some individuals.
Anyone suspecting they have a fish allergy should not eat flounder and consult their healthcare provider.
Cramps, vomiting, diarrhea, bloating, and swelling
Redness, pain, tongue swelling, cough
Throat closing, wheezing, tightness, and feeling faint
Mercury Content
Seafood can sometimes contain high levels of mercury, a heavy metal that can potentially cause adverse health effects.
For instance, fish like swordfish, shark, and certain tuna species all have a high mercury content.
On the positive side, while it does contain some mercury, flounder has a relatively low mercury content.
The FDA’s mercury in fish monitoring program 1990–2012 found that flatfish species, including flounder, had a mean mercury concentration of 0.056 PPM. This data was based on 71 samples collected over 18 years.
By comparison, popular fish like cod (0.111 PPM), canned tuna (0.126 PPM), and bass (0.167 PPM) all contain more mercury than flounder.
Joint advice from the EPA and FDA list flounder among the ‘best choices’ for eating fish for pregnant or breastfeeding women and children.
Is Flounder Sustainable?
‘Sustainability and conservation’ is moving away from nutrition, but many people do care about choosing sustainable fish.
If you are one of these people, then here are the ratings for flounder from several renowned sustainability and conservation organizations.
The Marine Conservation Society
The Marine Conservation Society gives flounder an ‘OK’ rating as opposed to a ‘best choice’ or ‘avoid’ rating.
This rating is based on good stock status, but some issues with a lack of management plans and the capture method.
Monterey Bay Aquarium Seafood Watch gives a ‘buy’ rating to flounder caught in Alaska, California, Oregon, and Washington.
They also award the ‘buy’ rating to winter flounder caught in the U.S. Georges Bank or Gulf of Maine, summer flounder in the U.S. Atlantic caught with bottom trawls, Southern flounder caught in Texas, and Arrowtooth flounder caught in British Columbia, Canada.
Aside from this, the ‘buy’ rating goes to all flounder in the United States and globally that are certified by the Marine Steward Council (MSC).
An ‘avoid’ rating is given to blackback flounder caught in the U.S. or Canadian Atlantic with bottom trawls, summer flounder caught with set gillnets in the U.S. Atlantic, witch flounder and yellowtail flounder in the U.S. Atlantic, and California flounder caught in Mexico.
As we’ve seen throughout this article, flounder is an excellent source of protein, provides a broad range of vitamins and minerals, and offers a modest amount of omega-3.
Its protein density is one of the highlights, making it an excellent choice for people looking to increase their protein or lower their calorie intake.
Overall, aside from for people with rare finfish allergies, flounder can add a lot of nutritional value to the typical diet.
Michael works as a nutritionist in a community setting and holds a Master's degree in Clinical Nutrition. He is a Registered Associate Nutritionist (ANutr) with the Association for Nutrition (AfN), and has published peer-reviewed research.
