Omega-3 fatty acids play crucial roles in human health and physiology. Fish is a fundamental component of a healthy diet and one of the best sources of these essential fatty acids. But does that mean all fish contain omega-3s? You might be surprised to learn that not all fish are created equal regarding these nutrients. This article will examine omega-3 fatty acids, their benefits, which fish are the best sources, and how much is recommended to optimize health and well-being.
What are Omega-3 Fatty Acids?
Omega-3 fatty acids represent a class of polyunsaturated fatty acids (PUFAs), distinguished from saturated and monounsaturated fatty acids by the presence of two or more double bonds between carbons within the fatty acid chain. Omega-3s get their name by having a carbon-carbon double bond located at three carbons from the methyl end of the FA chain. While several different types of omega-3s exist, there are three that the scientific community has focused on for their health benefits: alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA).
The human body can only form carbon-carbon double bonds after the ninth carbon from the methyl end; therefore, omega-3s are considered to be essential fatty acids, meaning we must obtain them from the diet. ALA is present in plants such as walnuts, flaxseed, soybean oil, and canola oils. Therefore, most people in the United States meet their ALA needs through foods they eat in their standard diets.
While ALA can be converted into EPA and DHA, studies show the conversion rate is meager, with approximately 8% converted to EPA and 0%-4% converted to DHA. Therefore, consuming EPA and DHA directly from food is the most effective way to meet physiological needs.
EPA and DHA are found primarily in fish, fish and krill oil, and oil derived from marine microalgae.
The Essential Roles of Omega-3s in Human Health
After over 30 years of research, there is little doubt that omega-3 fatty acids play a crucial role in maintaining health. They are significant structural components of cellular membranes and are especially rich in the retina, brain, and spermatozoa. Omega-3 fats are necessary from conception and play vital roles in the growth and development of the fetal central nervous system, optimal motor skills, and visual development in infants and children. Furthermore, evidence shows that omega-3s play a preventative role in several common conditions of Western Civilization, including Chron’s disease, breast, colon, and prostate cancers, hypertension, and rheumatoid arthritis.
However, the most robust evidence relating to omega-3 fats and disease is the inverse relationship between these nutrient and the occurrence of coronary heart disease and its complications. Omega-3s appear to, by various mechanisms, prevent deaths from coronary disease and reduce the risk of overall mortality.
One study found that men who consumed salmon ≥ 1 time per week had a 70% less likelihood of cardiac arrest. Another study established that overall mortality was decreased by 29% in men with cardiovascular disease who consumed omega-3s from fish or fish oil. Moreover, a large prospective cohort study including over 20,000 U.S. male physicians found that consuming ≥1 fish meal per week was associated with a 52% lower risk of sudden cardiac death compared with <1 fish meal per month.
While fish provide many helpful nutrients, researchers agree that increased intake of omega-3 fatty acids provides many of these health benefits.
Types of Fish that are High in Omega-3 Fatty Acids
Not all fish are high in omega-3 fatty acids. Generally speaking, fattier fish are higher in omega-3 fats, whereas fish lower in fat content – such as bass, tilapia, cod, and shellfish contain lower levels. When looking for higher-fat fish, look for a firmer and oilier texture, richer flavor, and deeper color. Often, cold-water fish fit this description.
The USDA National Nutrient Database has a comprehensive list of foods containing DHA and EPA arranged by nutrient content. Additionally, according to FoodData Central, some fish that are the richest in both omega-3 fatty acids include:
- Mackerel (Atlantic & Pacific): 1,900 mg EPA + DHA per 3 ounce serving
- Herring: 1,330 mg EPA + DHA per 3 ounce serving
- Anchovies: 1,200 mg EPA + DHA per 3 ounce serving
- Sablefish (Black Cod): 1,200 mg EPA + DHA per 3 ounce serving
- Salmon (Atlantic, Chinook, Coho): 1,200 mg EPA + DHA per 3 ounce serving
- Sardines (Atlantic & Pacific): 900 mg EPA + DHA per 3 ounce serving
- Swordfish: 643 mg EPA + DHA per 3 ounce serving
- Trout: 621 mg EPA + DHA per 3 ounce serving
While general guidelines are helpful, the omega-3 content of fish varies widely and will depend on the diet of the fish itself. For wild fish, the location and environmental variables can affect the diet and, therefore, the omega-3 content of the fish. For farm-raised varieties, the farmer’s choice of food pellets will impact the omega-3 content of the fish. Studies show that farmed fish usually have higher levels of EPA and DHA than wild-caught fish, but it depends on the food they are fed.
One study measured the fatty acids of 5 different salmon species from various regions in the United States and found that omega-3 content ranged from 717 mg to 1,533 mg per 100 grams of fish (3.5-ounce serving). Furthermore, another study found that the levels of EPA and DHA in farmed Scottish Atlantic Salmon significantly decreased between 2006 and 2015. Consequently, the researchers identified that in 2015, one would require double portion sizes, compared to 2006, to satisfy the recommended EPA + DHA intake levels endorsed by health organizations.
Recommended Intake of Omega-3s from Fish Sources
The American Heart Association (AHA) recommends eating two servings of fatty fish weekly. According to the AHA, a serving of fish is defined as 3 ounces of cooked or ¾ cup of flaked fish. The U.S. Food and Drug Administration (FDA) recommends eating 2-3 servings of fish weekly, even for those who are pregnant or breastfeeding. The FDA defines a serving of fish as about 4 ounces, measured before cooking, or the size and thickness of the palm of your hand (if you’re an adult). The FDA noted a maximum level of consumption of 12 ounces per week, which is consistent with the 2015-2020 Dietary Guidelines for Americans. For children, serving sizes should be smaller, adjusted for age, and eaten 1-2 times weekly. Even though fish are valuable sources of protein, omega-3s, vitamins, and minerals, nearly all fish contain at least traces of contaminants to be wary of.
Methylmercury, one of the most common contaminants found in fish, is a naturally occurring element that can be harmful to the brain and nervous system if a person is exposed to too much over time. Fish absorb methylmercury from their food, which tends to build up more in larger fish species. While limiting mercury in the diet is important, specific fish species tend to be lower in contaminants and can be included more regularly. The FDA has a list of seafood categorized as “Best Choices,” “Good Choices,” and “Choices to Avoid” based on mercury levels, which can be found here. Seafood options on the “Best Choices” list include commonly eaten fish, such as Cod, Herring, Mackerel, Salmon, Sardine, Shrimp, Tilapia, Trout, and Tuna. Other ways to minimize exposure to contaminants in fish include eating various fish and checking the FDA website for the latest advisories.
Sources Other than Food for Obtaining Adequate Levels of Omega-3s
Omega-3 FAs are present in several dietary supplements if food sources, like fish, are inaccessible. Options can vary, including fish oil, krill oil, cod liver oil, and vegetarian alternatives containing marine algal oil. And unlike fish and seafood, omega-3 supplements are less likely to contain contaminants because they can be removed during processing and purification.
Formulations of dietary supplements can vary wildly, so if an omega-3 supplement is something you’re considering, be sure to read more about finding the right product here.
Adequate intake of omega-3 FAs, particularly DHA and EPA, is vital for human health across the lifespan. While fish are the primary source of DHA and EPA, not all fish contain substantial amounts of these fundamental fatty acids. Furthermore, some fish may contain high amounts of environmental contaminants, which may be harmful over time. Therefore, the best strategy is to regularly consume fish higher in DHA and EPA and lower in environmental pollutants.
The FDA recommends eating 2-3 servings of fish from the “Best Choices” list weekly, with one serving being about 4 ounces, measured before cooking, or the size and thickness of the palm of your hand (if you’re an adult). Since the omega-3 content of fish can vary wildly, it’s wise to occasionally test your omega-3 index to ensure you are consuming enough to meet your specific needs.