Update: I now recommend Extra Virgin Cod Liver Oil from Rosita as my preferred cod liver oil product. For more information, read this article. You can purchase EVCLO here.

Summary

Sorry, folks. Another long one. It was unavoidable, though, because I really did want this to be a “definitive guide” that covers all (or at least most) of the relevant issues involved with choosing a fish oil. Here’s a summary for the time-challenged:

There are seven important factors to consider when choosing a fish oil: purity, freshness, potency, nutrients, bioavailability, sustainability, and cost.

Not all fish oils are created equal. It’s essential to do your homework and make an informed choice. Many fish oils are oxidized or made with poor quality ingredients, and may actually cause health problems instead of solving them.

The potency of various products depends not only upon the levels of EPA and DHA, but also upon the molecular structure of the fats in the oil, which in turn affects absorption.

Natural fish oils are better absorbed than purified fish oils. Preliminary evidence suggests that krill oil (KO) may be better absorbed than fish oil, and anecdotal reports indicate that KO may be more effective for some than fish oil for reducing inflammation in some people.

Many fish oils are made from fish that are endangered. Choose products made from fish that are certified by organizations such as the Marine Stewardship Council.

Introduction

So far in this series we’ve looked at why fish is superior to plant-based sources of omega-3. We’ve examined the importance of reducing consumption of omega-6 fats. We’ve considered how much omega-3 is needed to support health and treat disease. We’ve revealed that concerns about the safety of fish consumption have been overblown, and that eating fish regularly is not only safe, but incredibly beneficial. And in the previous article we compared the benefits of eating fish to taking fish oil.

In this final article of the series we’re going to take a closer look at fish oil. Fish oil has become wildly popular these days. Most people who are at least relatively health conscious understand that they need omega-3 in their diet, and are probably not getting enough from food (unless they eat a lot of fish).

Health care practitioners have caught on, too. I constantly hear both conventional and alternative practitioners telling their patients to take fish oil. In fact, I was listening to a podcast last week by one popular health and fitness guru in the paleo/primal world, and he advises his clients to take up to 20 grams of fish oil a day. That made me cringe.

Why? Because what most people – including health care practitioners – don’t seem to understand is that not all fish oils are created alike.

There’s a tremendous difference in the ingredients, purity, freshness and therapeutic benefit of the fish oils available today. The supplement industry is rife with false claims and unsavory companies that are far more interested in profiting on the fish oil craze than they are in your health and well-being.

Recommending that people take up to 20g/d of fish oil without conveying the importance of choosing a high quality fish oil, and teaching them how to do that, is irresponsible and possibly dangerous. Taking 20g/d of a poor quality, oxidized fish oil could dramatically increase oxidative damage and inflammation – which is of course exactly the opposite of the desired effect.

In this article, I’ll focus more on dispelling common misconceptions about fish oil and helping you to choose the best product for your needs.

Factors to consider when buying fish oil

There are seven primary variables to be aware of when shopping for a fish oil:

Purity. The oil must meet international standards for heavy metals, PCBs, dioxins and other contaminants. Many do not – even when they claim they do. Freshness. Omega-3 oils are susceptible to oxidation, which makes them rancid. Rancid oils are pro-inflammatory and contribute to the diseases you’re trying to relieve or prevent by taking fish oil in the first place! Potency. In order to have the desired anti-inflammatory effect, fish oil must contain an adequate amount of the long-chain omega-3 derivatives EPA and DHA. DHA is especially important. Nutrients. All fish oils contain some amount of EPA and DHA. However, fish liver oil (from cod, skate or shark) also contains naturally occurring fat-soluble vitamins that are difficult to obtain from foods. Bio-availability. The ability to absorb the beneficial components of fish oil is based on the molecular shape of the fatty acids. The more natural the structure the better. Sustainability: The fish should be harvested in a sustainable manner and species that are under threat should be avoided. Cost: the product must be relatively affordable to be practical for most people.

Purity

Many species of fish are known to concentrate toxic chemicals like heavy metals, PCBs, and dioxins which can cause serious disease, especially in children and developing fetuses. In a previous article I explained how these chemicals are typically not a concern when eating whole fish, because fish also contains selenium. Selenium binds to mercury and makes it unavailable to tissues, thus protecting against any damage it may cause.

And while fish constitute only 9% of our dietary intake of dioxins and PCBs, high doses of fish oils taken every day (as is often recommended) may raise this percentage significantly and expose us to undesirable levels of these toxins.

To address this, fish oil manufacturers use a process called molecular distillation to remove the toxins from the oil. When done correctly, molecular distillation is capable of reducing the toxins in fish oil to levels considered to be safe by the EPA and other agencies.

Although almost any fish oil manufacturer will tell you their product is free of these toxins, independent lab analyses tell a different story. Just last month (March, 2010), a lawsuit was filed in California court against the manufacturers of ten popular fish oils because they contained undisclosed and (possibly) unsafe levels of contaminants.

Unfortunately, this kind of deception is all too common in the supplement industry. That’s why it’s essential that you ask for something called a Certificate of Analysis (COA) from the manufacturer before you buy their product. A COA is an analysis performed by an independent lab to measure the ingredients of a product and confirm whether it lives up to the claims made by the manufacturer.

If the manufacturer won’t provide a COA, I start to get suspicious. This is standard practice in the industry and there’s no reason they shouldn’t be happy to show you theirs. Make sure that the independent lab they use is in fact independent and is preferably accredited, sponsored by a government agency, or has a solid reputation in the field.

This may seem like unnecessary paranoia, but when it comes to the possibility of ingesting powerful neurotoxins, it pays to do your homework.

In general, fish that are lower on the food chain like sardines and anchovies naturally have a lower concentration of contaminants. For this reason, it may be wise to look for a product made from these fish.

So what levels of these toxins are safe? As you might imagine, there is some disagreement on this question since there is no single governing body that determines acceptable levels. However, the standards that are most often followed by fish oil manufacturers are summarized in the table below.

* ppt = parts per trillion

* ppb = parts per billion

In a previous article we discussed selenium’s protective effect against mercury toxicity. If you are taking large doses of fish oil, and not eating any whole fish, it may be wise to ensure another regular source of selenium. Brazil nuts are by far the highest dietary source, with 1917mcg of selenium per 100g. (But they are also very high in n-6, so watch out!)

Freshness

I have written extensively about the dangers of oxidized, rancid oils. They promote oxidative damage and increase inflammation, both of which are risk factors for nearly every modern disease.

The more unsaturated an fat is, the more vulnerable it is to oxidation. Long-chain, omega-3 fats found in fish oil are the most unsaturated of the fats, and thus the most susceptible to being damaged.

This is why it’s absolutely crucial to ensure that the fish oil you select is fresh and not rancid. Once it has gone rancid, it will have the exact opposite effect on your body than you want it to.

The first thing to do is to check something called the “peroxide value” on the COA. This is a measure of rancidity reactions in the oil that have occurred during storage. and should be less than 5 meq/kg.

If this checks out, and you decide to order that product, break open a capsule once you receive it. There should be no “fishy” odors. They should smell like the ocean, but not like a rotten fish. They should also not have a strong lemon or lime scent, which could be an indicator that the manufacturer is trying to mask the rancidity.

A common misconception is that you can determine the quality of a fish oil by freezing it. The theory goes that if you freeze the oil and it is cloudy, it’s rancid. That is not the case. All fish contain saturated and monounsaturated fatty acids, albeit in small amounts. These fatty acids make the capsules appear cloudy when frozen in products that contain whole fish oil (i.e. Vital Choice’s Wild Salmon Oil).

Potency

This is another area surrounded by significant controversy. Some argue the levels of individual constituents in fish oil aren’t paramount. Scientists discovered the healthful effects of omega-3s by studying people with fish-heavy diets, before supplemental fish oil even existed. Clinical trials using supplemental fish oils over the past few decades have contained widely variable levels of both long-chain omega-3 derivatives (EPA and DHA), and not super-high concentrations of either or both.

However, due to poor conversion of ALA to EPA and DHA, unless you are eating fish it is very likely you are deficient in long-chain omega-3s.

Following this line of reasoning, the DHA content in particular of fish and fish oils does seem important if we wish to obtain the best possible therapeutic effect. Many recent studies demonstrating the anti-inflammatory potential of fish oil used a daily dosage of DHA in the range of 1-3 grams. What’s more, foods like salmon roe that have been prized by traditional cultures for their nourishing and healing effects contain large amounts of DHA. A single 6 oz. serving of salmon roe contains 1 g of DHA. (In fact, this would be the best way by far of supplementing with DHA if money were no object. (Unfortunately, wild salmon roe goes for about $28/serving.)

The suggested DHA dose will of course depend upon the condition being treated. If you have a chronic inflammatory condition (heart disease, arthritis, Crohn’s or ulcerative colitis, etc.) I would suggest taking between 1 and 2 grams per day. If you are taking it simply for health maintenance, 500 mg is probably sufficient.

Unfortunately, many fish oils do not have significant amounts of DHA. This means you’d have to take an impractically high number of capsules each day to obtain the therapeutic dose. This is not desirable, since all unsaturated oils (including fish oils) are subject to oxidative damage. We don’t want to take large quantities of them for this reason.

Remember to check the label and ensure that your product has approximately 200-300 mg of DHA per capsule. This will allow you to achieve the therapeutic dose by taking no more than 3 capsules twice a day.

Nutrients

All fish oils contain some amount of EPA and DHA, the long-chain omega-3 derivatives that provide the majority of the anti-inflammatory benefits seen in studies. However, fish liver oils (from cod, skate or shark) contain significant amounts of vitamins A and D in addition to EPA and DHA. Vitamins A and D are fat-soluble nutrients that are crucial to human health. Vitamin D, in particular, is difficult to obtain from commonly eaten foods – especially now that eating seafood carries a much higher risk of contamination with toxins.

Fermented cod liver oil is even more beneficial, because it contains vitamin K2. Vitamin K2 has been called “the missing nutrient” because it was only recently discovered, and many people are deficient in it.

It has been commonly believed that the benefits of vitamin K are limited to its role in blood clotting. Another popular misconception is that vitamins K1 and K2 are simply different forms of the same vitamin – with the same physiological functions.

New evidence, however, has confirmed that vitamin K2’s role in the body extends far beyond blood clotting to include protecting us from heart disease, ensuring healthy skin, forming strong bones, promoting brain function, supporting growth and development and helping to prevent cancer – to name a few.

Cod liver oil was traditionally processed by fermentation, which is likely to make it more absorbable and bio-available. Processing by fermentation also avoids the use of heat, which can damage the fragile fatty acids and cause fish oils to go rancid. Unfortunately, I am aware of only one company that sells fermented cod liver oil at this time (see below).

Bio-availability

The ability to absorb the beneficial components of fish oil is based on the molecular shape of the fatty acids. In short, the more natural the structure and the less it is chemically altered, the better.

This is true for any nutrient, of course, and it explains why I am always in favor of obtaining nutrients from food or food-based sources when possible. Each additional step in processing from the natural state of a food to extract or isolate nutrients introduces the potential of damaging the nutrient, or changing it’s chemical form so that it’s more difficult to absorb or affects the body in a different way.

When it comes to fish oils, there are three forms currently available on the market:

Natural triglyercide oil. This is what you get when you “squeeze” the whole fish and extract the natural oil from it. It is the closest to eating fish oil in its natural form, and is highly bioavailable. The drawback of this form is that, because it’s not concentrated, it usually has low levels of EPA and DHA. And because it isn’t purified, it can have high levels of contaminants such as heavy metals, PCBs, and dioxins. Ethyl ester oil. Occurs when natural triglyceride oil is concentrated and molecularly distilled to remove impurities. The ester form is still in a semi-natural state because it is the result of a process that naturally occurs in the body. The advantage to this form is that it can double or triple the levels of EPA and DHA. Synthetic triglyceride oil. This form occurs when natural triglycerides are converted to ethyl esters for concentration (as above), but then re-converted into synthetic triglycerides. The original position of the triglyceride’s carbon bonds change and the molecule’s overall structure is altered, which impacts the bioavailability of the oil.

Studies on absorption of the various types of fish oil suggest that, unsurprisingly, the natural triglyceride form is absorbed better than the ethyl ester form, which in turn is absorbed better than the synthetic triglyceride form.

One study by Lawson & Hughes in 1988 showed that 1 gram of EPA and 0.67 grams of DHA as natural triglycerides were absorbed 3.4 and 2.7 fold as well as the ethyl ester triglycerides.

In the previous article we saw that fish oils were better absorbed when taken with a high-fat meal. In another study by Lawson & Hughes later the same year, they showed that the absorption of EPA & DHA from natural triglycerides improved from 69% with a low-fat meal (8g total fat) to 90% with a high-fat meal (44g total fat). Absorption of both EPA and DHA from ethyl ester oils was increased three-fold from 20% with a low-fat meal to 60% with a high fat meal.

What about krill oil?

In addition to the three types of fish oil listed above, there is another type of oil that provides EPA & DHA: krill oil. Krill oil (KO) is extracted from Anarctic krill, Euphausia superba, a zooplankton crustacean rich in phospholipids carrying EPA and DHA. Krill oil also contains various potent antioxidants, including vitamins A & E, astaxanthin, and a novel flavonoid whose properties are not yet fully understood.

Krill oil has a unique biomolecular profile that distinguishes it from other fish oils. While EPA and DHA in fish oils comes in the form of triglycerides, the EPA and DHA is already incorporated into phospholipids, which facilitates the passage of the fatty acids through the intestinal wall. This increases the bioavailability of the EPA and DHA and improves absorption and assimilation.

Werner et al demonstrated essential fatty acids in the form of phospholipids were superior to essential fatty acids as triglycerides in significantly increasing the phospholipid concentrations of EPA and DHA in mice.

In a human study, Bunea et al compared the effect of krill oil and fish oil on blood lipids, specifically total cholesterol, triglycerides, LDL, and HDL. Krill oil was given at dosages of 1g/d, 1.5g/d, 2g/d or 3g/d, and fish oil was given at a single dose of 3g/d. The authors found the following:

KO at a daily dose of 1g, 1.5g, 2g or 3g achieved significant reductions of LDL of 32%, 36%, 37% and 39% respectively. Patients treated with 3g fish oil daily did not achieve a significant reduction in LDL.

HDL was significantly increased in all patients receiving KO. HDL increased 44% at 1g/d, 43% at 1.5g/d, 55% at 2g/d and 59% at 3g/d. Fish oil taken at 3g/d increased HDL by only 4%.

in all patients receiving KO. HDL increased 44% at 1g/d, 43% at 1.5g/d, 55% at 2g/d and 59% at 3g/d. Fish oil taken at 3g/d increased HDL by only 4%. KO did not decrease triglycerides significantly at 1g and 1.5g. However, KO reduced triglycerides by 28% at 2g/d and 27% at 3g/d. Fish oil at 3g/d did not achieve a significant reduction of triglycerides.

Blood glucose levels were reduced by 6.3% in patients receiving 1g/d and 1.5g/d of KO, and 5.6% in patients receiving 2g/d and 3g/d of KO. A daily dose of 3g of fish oil reduced blood glucose by 3.3%.

Thus, in this study krill oil led to a significantly greater improvement in blood lipids compared to fish oil.

Note that the dosage of KO that obtained the best results, either 2g/d or 3g/d, is quite high. However, study participants received a maintenance dose of 0.5g/d for another 12 weeks after the therapeutic period of the study ended. These patients maintained the reductions in total cholesterol they attained in the study, and LDL, triglycerides and blood glucose were further reduced from baseline. There was a moderate decrease (of 3%) in HDL, but HDL was still significantly increased from baseline.

There is also unpublished research suggesting that 300 mg/d of KO reduces biochemical and subjective measures of inflammation and improves joint function and mobility in patients with rheumatoid arthritis (RA).

However, as this research is not published or peer-reviewed, and was sponsored by Neptune Technologies (the manufacturer of Neptune Krill Oil (NKO), I am cautious about interpreting its results.

So what does all of this information about bio-availability tell us?

Taking fish oil capsules with a high-fat meal is essential to improve absorption of EPA and DH. Even when taken with a high-fat meal, ethyl ester oils are absorbed only 66% as well as natural triglyceride oils. Krill oil appears to significantly improve blood lipids when compared to fish oils, possibly because of its unique phospholipid structure.

Sustainability

The sustainability of fish oil production is difficult to gauge. Some oils are produced as a byproduct of fish harvesting, and manufacturers claim that they are simply making use of something that would normally be discarded. While this is certainly better than harvesting fish solely for their oil, it still supports harmful fishing practices.

The safest bet is to only use fish oil that is made from fish that are certified by MSF or a similar organization, such as the Environmental Defense Fund. Vital Choice Wild Salmon Oil is one example, as is Jarrow Max DHA (which is made from anchovies and sardines, both of which are generally regarded as safe to eat from an environmental standpoint).

Cost

I cover cost in the recommendations section below.

Recommendations

Note: I have no affiliation with any of these companies. These are simply the products I recommend based on my research. It’s very likely that there are other good products that I missed in my search. This is not an exhaustive list.

Which product you might choose from this list depends in large part upon what your goals are.

I have provided product recommendations in two different categories: baseline, and supplemental. Those wishing to to maintain health and ensure adequate nutrient intake should choose a product from the “baseline” category. Those who are dealing with a chronic inflammatory condition should also choose a product from the baseline category, but should consider adding a product from the “supplemental” category.

However, keep in mind that the absorption of the natural triglyceride oils (like the Wild Salmon Oil and Fermented Cod Liver Oil below) will be 1.5 times greater than the ethyl ester oils in the supplemental section. As a rule of thumb, all purified and molecularly distilled oils are ethyl esters.

This means you have to take 1.5 times as much of the ethyl ester oils to get the same dose of DHA that you’d get from the natural triglyceride oils. For example, Vital Choice Wild Salmon Oil has 220 mg DHA per serving. To get the same amount of DHA from Jarrow Max DHA, which is an ethyl ester oil, you’d have to take a serving that provides 333 mg of DHA.

Baseline

Green Pastures Fermented Cod Liver Oil and Butter Oil Blend (GP FCLO)

Ingredients: about 270 mg omega-3 (about 139 mg EPA, 83 mg DHA), about 1,100 IU vitamin D, about 2,300 IU vitamin A. Values listed are approximate (see disadvantages).

Price: $47.00 for 120 capsules, 2 capsules per serving. $0.78/serving.

Advantages: a whole-food product in its natural form, rather than a supplement. Is relatively low in EPA & DHA compared to other products, but contains high levels of vitamin D, as well as vitamins A & K. The fat soluble vitamins A, D & K2 are important co-factors and likely improve the absorption and assimilation of EPA & DHA. Addition of grass-fed butter oil increases levels of K2. Cold-processed with fermentation, which means this is the least oxidized product available.

Disadvantages: levels of PCBs are posted on Green Pastures’ website here, but I’ve been unable to obtain information on heavy metals or dioxins. The EPA and DHA levels are what would be expected in a whole food product, but may not be high enough for a significant anti-inflammatory effect. Values for vitamins A, D, EPA and DHA are approximate and vary batch to batch due to fermentation processing method. Peroxide values are not provided, but because it is processed without heat they are likely to be very low.

Notes: because fermented cod liver oil contains vitamins A, D and K2 in addition to EPA and DHA, and because most people are deficient in some or all of these nutrients, this is currently the only product I recommend to everyone – patients, family and friends – regardless of their health status.

Vital Choice Wild Salmon Oil (VC WSO)

Ingredients: 600 mg of omega-3 (240 mg EPA, 220 mg DHA), 340 IU vitamin D, 2,060 IU vitamin A (per 3 1,000 mg softgels).

Price: $40 bottle, 180 capsules. 3 capsules/serving, $0.68/serving.

Advantages: processed without heat using micro-filtration, which retains naturally occurring vitamins A and D. Fatty acids are in their natural triglyceride form, which makes them more absorbable. Also contains astaxanthin, which protects the oil from oxidative damage and rancidity. Contains more EPA and DHA than GP FCLO. Nutrient levels are more consistent from batch to batch and certification is performed by independent, not-for-profit organization (NSF International).

Disadvantages: when compared to GP FCLO, does not have vitamin K2 and the dose of vitamin D is significantly lower. Otherwise no disadvantages.

Supplemental

Jarrow Max DHA

Ingredients: 600 mg of omega-3 (250 mg DHA, 36 mg EPA) per capsule; one capsule is one serving.

Price: $14.85 (at Vitacost) for 180 capsules. $0.08/serving.

Advantages: even after considering the differences in absorptions between Jarrow Max (an ethyl ester) and the two natural triglyceride oils listed above, Jarrow Max is significantly cheaper. It’s possible to get 1g/d of DHA for $0.32. Made with anchovies and sardines, both of which are naturally low in contaminants. Jarrow faxed me their certificate of analysis, which checked out fine. This is a good choice for those wishing a high-dose of DHA in addition to eating fish or taking one of the natural triglyceride oils above.

Disadvantages: has a 7:1 ratio of DHA to EPA. Although I believe DHA to be more beneficial than EPA, the research is mixed on this and some people report that they do better with EPA.

V-Pure Vegetarian DHA

Ingredients: 350 mg DHA, 50 mg EPA per serving, 2 capsules per serving.

Price: $21.95 for 60 capsules. $0.73 per serving.

Advantages: I received several emails from vegetarians asking me what I recommended they do to meet DHA needs. This is a DHA/EPA blend derived from marine algae, which is where oily fish get EPA & DHA in the first place. The algae in this product is organically grown and 100% free of toxins and contaminants. The capsules are quite small and can be easily swallowed.

Disadvantages: I haven’t seen much research on the marine-algae DHA/EPA blends. Although it’s plausible to assume their effects would be similar to fish oils, I’d like to see some studies backing that up. Likewise, I don’t know much about V-Pure as a company. Another potential issue is that the capsules have carrageenan in them, which has been shown to exacerbate intestinal inflammation in several studies. People with gut problems like IBS and IBD may want to avoid this product. Finally, at $0.73/serving this product is expensive. To get a therapeutic dose of 1g/d taking this alone, you’d have to take 9 capsules per day which be 4.5 bottles/month, or almost $100!

Tentatively Recommended

Neptune Krill Oil

Ingredients: 300 mg of omega-3 (90 mg DHA, 150 mg EPA) per serving, two capsules per serving.

Price: $16.86 for 60 capsules. $0.56/serving, 2 capsules per serving.

Advantages: KO has a unique phospholipid structure that appears to improve the absorption of EPA & DHA. At least one study suggests that KO is superior to fish oil in improving blood lipids. KO also contains vitamins E & A, as well as astaxanthin, an antioxidant claimed to be 10 times more potent than other carotenoids. KO capsules are much smaller than fish oil capsules, are easier to swallow, and many report they don’t cause the burping common with other fish oil capsules. Several anecdotal reports suggest that krill oil can be more effective than fish oil in reducing inflammation for some people.

Disadvantages: there are few studies demonstrating the effectiveness of KO, whereas fish oil has decades of research behind it. Most of the studies that do exist on KO were sponsored by Neptune, the largest manufacturer of KO. The dosages used in the study on KO and blood lipids were very high, and taking KO at those dosages would be expensive. (However, the therapeutic dose of 2-3g/d would only be necessary for 12 weeks, as the maintenance dose of 0.5g seemed to maintain the benefits attained during the therapeutic period.) The sustainability of krill harvesting is controversial.

The reason KO gets a tentative recommendation is that there’s still comparatively little research supporting its use, and because I am still uncertain about the environmental impact of harvesting the krill for the oil.