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About Omega 3 Fish Oils

Everything You Need to Know About Fish Oil Supplements

By Deanna Minich, PhD

Have you been told that you need to take fish oil supplements by your healthcare practitioner? It can be confusing to select a product with all the brands on the shelf. Before you buy and start popping the soft gels down or drinking the lemony fish oil liquid, you may want to become knowledgeable about what to look for. Here are some common questions that may come to mind:

What do all the terms mean – “Omega-3s,” “EPA,” and “DHA”?

It can get confusing to juggle all the fish oil terminology. There is a separate vocabulary that you need to have a handle on before starting to select a supplement. Here’s a quick list to get you started with some basics to help you navigate the waters of the many products on the market:

Fish Oil: A generic descriptor for omega-3 supplements from fish; It can contain any amount of omega-3 fatty acids and be from any fish source.

Cod Liver Oil: A specific oil form of omega-3s that will contain other fatty compounds from the liver of the cod fish, including vitamins A and D

Omega-3s: The term given to the fatty acid family of essential fats that you need to take in from your diet. “Fish oil supplement” and “omega-3 supplement” are often interchangeably used. There are many individual omega-3 fatty acids that differ in their carbon, or chain, length, as well as their fluidity. The main omega-3 fats that are touted with health benefits are the long-chain, highly-fluid, fish- and algae-derived, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Another shorter, less fluid form of an essential omega-3 fat is alpha linolenic-acid (ALA), which comes from plant sources like leafy greens, flaxseed, nuts, and seed oils.

EPA: The acronym for eicosapentaenoic acid, an essential, long-chain omega-3 fatty acid found in fish and shellfish. EPA can be converted in the body to other longer-chain fats like docosahexaenoic acid (DHA).

DHA: The acronym for docosahexaenoic acid, an essential, long-chain omega-3 fatty acid found in fish, shellfish, and algae. EPA can be converted into this longer-chain fat, and a small percentage of DHA can be converted back into DHA.

Triglycerides: The structure in which fats are typically stored within the human body and animals, consisting of three individual fatty acids connected to a glycerol backbone.

Ethyl Esters: A type of delivery system for fats, like omega-3 fatty acids.

How do I know if I need to take omega-3 fatty acids in a supplemental form?

Your health care practitioner or pharmacist will assess whether you have the need for supplemental omega-3 fatty acids.

What conditions can omega-3 fatty acids help?

Autoimmune Conditions
Bipolar disorder
Chronic Fatigue Syndrome
Coronary heart disease
High blood fats (e.g., triglycerides)
High blood pressure
Inflammatory Bowel Disease
Rheumatoid arthritis

When you start to look at fish oil supplement information on the Internet, you may find that they are popular for just about everything. Part of the reason why may be because of where they are located in the body. They are part of virtually every cell in the body, in the outer membrane and in the inner membrane that surrounds the DNA. Therefore, they play an integral role in cell function and how cells communicate within and amongst each other. As a result, you might anticipate they might have wide application to several body systems.

While they are taken orally for a number of health issues, everything from heart disease to depression to arthritis to cognition, there are varying degrees of evidence for use. There is very good evidence that omega-3s from fish or fish oil supplements can assist in lowering blood levels of triglycerides (“hypertriglyceridemia”) by 20-50% (1). It seems that eating two servings of fish per week can also help reduce the risk of developing cardiovascular disease, such as heart attack, and may help to lessen the chance of death in people who have previously had a heart attack.

The other conditions for which omega-3s have been touted do not have the same convincing degree of evidence as we see with these cardiovascular-related conditions. Fortunately, studies on omega-3 supplementation seem to be regularly published, so data continues to collect to provide a better sense of their benefit.

When is it advised NOT to take fish oil supplements?

Again, it is important to listen to your practitioner when it comes to taking any supplements and let them know about any other supplements and/or medications you may be taking. When it comes to fish oil, there are definitely some things to watch for. If you are taking supplemental herbs or other dietary supplements that can influence blood clotting, blood thickness, or blood pressure, you may want to have your practitioner closely monitor the amount of fish oil you are supplementing with since there could be an enhanced, combined effect.

Here are some herbs/supplements with blood clotting and blood platelet effects to note (1):  angelica, clove, danshen, garlic, ginger, ginkgo, Panax ginseng, red clover, turmeric, willow, and others. Here are some with hypotensive effects: andrographis, casein peptides, cat's claw, coenzyme Q-10, fish oil, L-arginine, lycium, stinging nettle, theanine, and others.

If you are taking any drugs that do similar things, ensure that your practitioner regularly monitors your clotting time and/or blood pressure. If you are undergoing surgery of any type, let your physician know that you are on fish oil supplements as your clotting time may change under these circumstances.

How do the omega-3 fats work in the body?

Because omega-3 fats are not made in the body, they are essential to take in from food or supplements. That is the reason they are called, “essential fatty acids”. There is a large family of omega-3 fats, with some of them being shorter and some of them longer in length. Some of them are more fluid and flexible than others because of a specific chemical arrangement between the carbon bonds in the fat chain. The longer-chain omega-3 fats, EPA and DHA, are used to make anti-inflammatory compounds in the body. Additionally, by competing with another essential fat in the body from another fat family (called “arachidonic acid” which is from the “omega-6 family”), they can lessen blood clotting and narrowing of the blood vessels.

Other functions of omega-3 fats besides relaxing blood vessels and reducing blood thickness include becoming a part of cell membranes, thereby altering their fluidity; playing a role in heart rate and rhythm perhaps due to their incorporation in the heart tissue; and influencing the metabolism of fats in the liver. 

Is it better to eat fish or take supplements to get my omega-3s?

This is a difficult question to answer.

There are a number of compelling studies on the benefits of eating fish when it comes to heart disease.  Of course, whole food sources of any nutrient tend to be preferred because you are getting the nutrient within the natural complex that it is contained within – in the case of fish, you get protein, an array of different fats, along with some antioxidant carotenoids like astaxanthin (present in red- or orange-colored shellfish like shrimp). However, due to contaminated waters, fish can contain appreciable amounts of toxins like the heavy metal, mercury, and chlorinated compounds like polychlorinated biphenyls (PCBs), dioxin, and dioxin-related compounds. When we get an accumulation of these toxins in our body, we may see adverse effects on our nervous system, and recent studies show that our metabolism and risk of developing obesity and diabetes can increase with high levels of certain pesticides in our body.

Fish that contain high levels of mercury include the fatty fish like shark, swordfish, king mackerel, tilefish (also called golden bass or golden snapper), and farm-raised salmon. Be sure to check the Environmental Working Group website ( for frequent updates on toxicity in fish. Knowing this information about fish, most organizations recommend limiting fish consumption to about two to four servings per week. A serving size is 85 grams, so eating no more than the upper limit of 340 grams is the general guideline for the week for most people. Of the fish sources to choose from, it is preferred to choose low-mercury-containing fish (see Table 2).

Since children are smaller and run the risk of greater toxin accumulation, it has been advised that they consume no more than 56 grams of fish per week. Women who are pregnant, are considering becoming pregnant, or who are lactating are advised to stay at the level of no more than 340 grams per week (about 3-4 servings). Another aspect to consider is the influence of the methods of preparing and cooking fish. Some research shows that broiling and baking fish is preferred and results in good effects on cardiovascular disease risk, but that eating fried fish may lead to increased risk (4).

The benefit of fish oil supplements relative to eating fish for your omega-3 levels is that you get the pure oil from the fish without the contaminants if you are buying a good quality fish oil. The oil in a good-quality supplement goes through many levels of processing that can result in lower amounts of contaminants. However, you will not be getting all the other nutritional aspects in fish that you would get from eating it. Therefore, a combination of the two would likely be the best scenario for most people.

Table 2. Omega-3 fatty acid content of fish (1)


Amount of omega-3s in a
84 gram serving

Rainbow trout
Salmon (Atlantic, Farmed)
Salmon (Atlantic, Wild)
Salmon (Chinook)
Salmon (pink)
Salmon (sockeye)
Tuna (light, canned)

0.15-2.0 grams
0.13-0.24 grams
0.42 grams
0.40 -1.0 grams
1.71-1.81 grams
0.34-1.57 grams
0.84-0.98 grams
1.09 - 1.83 grams
0.90 - 1.56 grams
1.48 grams
1.09 grams
0.68 grams
0.98-1.70 grams
0.26 grams

How much of an omega-3 supplement should I take?

You should follow the recommendation of your practitioner. Taking up to 3 grams per day is considered to be a relatively safe dose for most healthy people (1), but cardiovascular benefit can be achieved in some cases with doses as low as 500 mg per day (5). Dosing of 4 grams per day (or more) have been prescribed for patients for a number of concerns, including greatly elevated triglycerides. However, high dosing of EPA and DHA on a daily basis may be associated to changes in blood clotting and bleeding risk. High-dose fish oil should be taken under the supervision of a physician.

What should I anticipate if I take fish oil supplements?

Overall, there tends to be no tolerance issues in people who take 3-4 grams per day or less. For some, they may experience nausea, diarrhea, or a fishy aftertaste from burping up the oil. When the supplement is taken at a meal or taken in frozen form, there tends to be less of this effect. Also, if the soft gels are enteric-coated, they are less apt to break down in the stomach and cause burping. 

Does the fish source of the omega-3s matter?

Most omega-3 fatty acid supplements come from anchovies, mackerel, herring, and/or sardines. Cod liver oil is another source of omega-3 fats, but will also provide vitamins A and D. Be sure to have your vitamin levels of these fat-soluble vitamins measured if your healthcare provider has you taking cod liver oil.

While the fish oil source will not greatly make an impact on your health since all oils are extensively processed for the end product of EPA and DHA, you may want to consider products that include sustainable sources of omega-3 fats such as those from anchovies, sardines, and squid rather than threatened fish sources like Atlantic salmon, Pacific cod, and shark (7).

How do I know my fish oil is pure?

You may not want to take a fish oil supplement unless you know it’s pure. Purchasing from a very reputable manufacturer is one way of assuring a clean source. However, if you are unsure or if you don’t see a seal, logo, or statement on the label of the product stating that it has been tested for purity and potency, it is important that you contact the company and inquire about their quality measures on fish oil.

The manufacturer of your fish oil should be testing the raw marine oil that goes into the product as well as the final product.  It is important to ask your fish oil supplement manufacturer whether your supplement is third-party tested (meaning tested by an outside party) for pesticides, heavy metals (ask for more than just mercury – consider lead, arsenic, etc.), PCBs, dioxins, furans, yeast, mould, and harmful bacteria.

Fish oil is heavily processed and purified before it makes it into your supplement, including molecular distillation to remove contaminants.  A good fish oil will contain some amount of antioxidants, such as vitamin E, C, and even plant compounds like carotenoids and rosemary extract, to protect the oil from going rancid. You will also want to ask about disintegration time, or the time it would take for the supplement to dissolve in the stomach contents, along with whether they have tested it for shelf stability.

Which is better: triglycerides or ethyl esters?

Some studies suggest that the triglyceride form is more rapidly absorbed after taking it, while the ethyl ester form is absorbed at a slower rate. There may be benefits of each type of absorption. But, the bottom line is that both forms are absorbed and utilized by the body. Furthermore, both forms have been shown to lower high blood triglycerides (“hypertriglyceridemia”), which is one of the main reasons why people take fish oil supplements. A fish oil pharmaceutical product on the market contains the ethyl ester form of EPA and DHA. Some people may prefer the triglyceride form because they consider it more nature-identical, while others would prefer the ethyl ester form, which can be more highly concentrated, so they don’t have to take as much oil.

How do I read a fish oil supplement label?

There are a few key features of a fish oil supplement label that are worthwhile to note:


  1. Serving size is listed here. This is the amount you will need to ingest to get the fatty acid amounts listed below. Note that these particular soft gels are enteric-coated so they break down in the intestine and not the stomach, potentially reducing some of the  burping-up effects.

  2. This is the total amount of fish oil in the designated serving size.

  3. Here are the amounts of the long-chain omega-3 fats, EPA and DHA, contained in a serving. Notice that they are only 50% of the total fat amount provided in a serving. If you need to take 3 grams of EPA and DHA daily, you would need to take a total of 6 of these softgels in a day. Aim for higher amounts of these fats in a soft gel so you don’t have to take so many and so you don’t get all the other fats in the blend that aren’t omega-3s!.

  1. All the ingredients contained in this product. Note that it lists the gelatin from the softgel, the enteric coating, flavoring, and antioxidants to preserve the fish oil from rancidity.

  2. The distributor of the product and their contact information are listed here.


  1. Natural Products Database,, accessed 9/15/13.
  2. US Food and Drug Administration, Center for Food Safety and Applied Nutrition, Office of Seafood. Mercury levels in seafood species. Available at:
  3. US Environmental Protection Agency. Fish Advisories web page. Available at:
  4. Mozaffarian D, Lemaitre RN, Kuller LH, et al. Cardiac benefits of fish consumption may depend on the type of fish meal consumed: the Cardiovascular Health Study. Circulation 2003;107:1372-7.
  5. Jason Goodman, PharmD, RPh, Student Health Services, The Ohio State University,, Accessed 9/15/13
  6. Seafood Watch, Monterey Bay Aquarium,, Accessed 9/16/13.
  7., Accessed 9/23/13.


About the Author
Deanna Minich, PhD, FACN, CNS
Functional Medicine Nutritionist

Dr. Minich has a research background in essential fatty acid absorption and metabolism, and has worked for a decade with one of the largest global dietary supplement companies as a teaching clinician. She has trained in functional medicine with the “father of functional medicine,” Dr. Jeffrey Bland, as her mentor, and currently serves as faculty for the Institute of Functional Medicine. She has an academic background is in nutritional science, including a Master’s Degree in Human Nutrition and Dietetics from the University of Illinois at Chicago, and a Ph.D. in Medical Sciences (Nutrition) from the University of Groningen in The Netherlands.

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