Fish Oil: Just The Facts

Written by James C., M.S.(C), PT

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Fish Oil: Just The Facts by Alan Aragon

fish oil

The Dawn Of Fat Phobia

 If you have a few years under your belt, then you can still remember what I call the “Fat-Free 80’s.” Think back to a time when dietary fat was the enemy. Ah, yes… A time when fat-free products lined the outer shelves of the supermarket. A time when it was not a bad thing to get a box of Entemann’s cinnamon rolls, as long as they were the FAT-FREE cinnamon rolls. Health Valley made some positively disgusting fat-free cookies, along with a host of other fat-free products that tasted like sugary cardboard. And we can’t forget the 75% sugar weight gainer products, those were priceless. 1,000, 2000, 4,000 calories per serving, and all you had to do was mix about a cup of powder into your favourite drink. No worries though, these gainers were virtually fat-free!

What we were led to believe was that fat-free products equated to fat-free physiques. Unfortunately, that was far from the truth.

During the 1980’s, a disturbing climb in national obesity rates occurred, and steadily kept its course.Large behavioral trend studies such as the National Health and Nutrition Examination Study (NHANES II & III), the Behavioral Risk Factor Surveillance System (BRFSS), and the Calorie Control Council Report (CCCR) collectively showed a 31% increase in overweight prevalence from 1976-1991. The punch line? This increase in weight was accompanied by an 11% decrease in percentage of calories from fat (from 41.0% to 36.6%). The most recent report by the BRFSS shows a further decrease in fat intake to 33%, accompanied by an increase in obesity from 11.6% to 22.1%. This is a 90.5% increase in US obesity from 1990-2002[1].

It’s obvious that dietary fat is not the evil culprit in the expansion of the population’s waistline.

 A Brief Evolution Of Our Knowledge of Fats

 As indicated by the fat-free product boom a couple of decades back, there indeed was the widespread belief that ALL fats were a substance to be minimized, or avoided altogether. But with the forward march of research, we came to understand that different fats had different effects on health.

fish oil

Since it’s human nature to think in black and white terms, the great divide initially fell between saturated (SFA) and mono- or polyunsaturated fatty acids (MUFA & PUFA). SFA were thought to be the root of all evil, conjuring images of arterial plaque and eventual heart failure, while unsaturated fat was regarded as a universally angelic substance.

This turned out to be a gross oversimplification of reality. The intricacies and widely varying sources and subtypes of SFA is another article altogether, but suffice it to say that it’s not that simple to pigeonhole them as unhealthy. SFA are not created equal. They have markedly variable physiological effects from the detrimental all the way to the beneficial. Given this, it depends on which ones you want throw onto the theoretical chopping block. Stearic acid, an SFA abundant in meat & milk fat, has been consistently observed to actually reduce blood platelet aggregation [2]. This is a good thing. In contrast, trans fats (found in high concentrations in commercially baked goods as well as processed & fried foods)  have been observed to negatively impact blood lipids by not only lowering HDL, but increasing LDL as well [3].

Ironically, experimental research exists on healthy humans showing the least fat was oxidized on the MUFA fat dietary treatment, and the most fat oxidized on a trans fat diet [4].

This result echoes what’s been seen in rats as well. It appears that the tighter the control of the study, the less “superior” unsaturated fats turn out to be for any presumed effect on body composition compared to SFA. Throw in the fact that a reducing SFA intake and increasing the degree of unsaturation of fatty acids in the diet reduces testosterone levels [5], and then you have yet another wrinkle in the mix to concern yourself with.

Then you have medium-chain triacylglycerols (MCT), which are SFAs that exhibit physiological behavior that’s closer to carbohydrate than fat.

MCT has been hyped to death by those who sell it. But the point is that they are a type of SFA that may potentially have minor benefits on body composition. I personally wouldn’t spend a dime on them, but they nevertheless illustrate the fact that SFAs are a complex and highly varied group of compounds in terms of physiological effect. As always, the effects of each type of fat undoubtedly vary with the population in question, as well as individual response.

fish oil

 Finally, with the black and white fallacy of saturated versus unsaturated fats out of the way, we can now shift the focus on fish oils, which happen to be a rich source of a particular class of fatty acids under intense study, the omega 3’s. 

Enter The Omega-3 Fatty Acids

Omega-3 fatty acids are essential for normal growth and development, but are noted specifically for their powerful influence over multiple physiological processes.

Alpha-linolenic acid (ALA), one of the two essential fatty acids (EFA) that the body cannot biosynthesize and must get from the diet, is an omega-3. EFA are precursors to a class of biologically significant compounds called eicosanoids, which include prostaglandins, leukotrienes, and thromboxanes. Eicosapentanoic acid (EPA) and docosahexanoic acid (DHA) can be derived from fish oil, and to a lesser degree, flaxseed oil. Consumption of EPA and DHA has an appreciable number of positive health effects, including decreases in blood platelet aggregation, lowered blood pressure, enhancement of smooth muscle function, decreased inflammation, alleviation of dyslipidema, and treatment of mood disorders [6-9]. There’s even emerging evidence pointing to the benefits of omega-3 fatty acids on bone health [10].

Archaeological research postulates that humans were  biologically designed to thrive on a diet whose ratio of omega-6 to omega-3 fatty acids was approximately 1:1, and unlikely greater than 4:1.

fish oil

Today, consumption of n-6 to n-3 fatty acids is estimated at roughly 25:1 [11]. This is due in part to a predominance of omega-6 oils available commercially in our food supply (corn oil, sunflower oil, safflower oil, refined packaged grain products & pastries) and a relative minority of omega-3 sources (fatty marine fish such as salmon, mackerel, herring, and flaxseed oil, walnuts, & small amounts in canola oil). Industrial production of omega-6-rich animal feeds has also resulted in animal tissues (livestock, eggs, and cultured fish) rich in omega-6 and poor in omega-3 fatty acids. This disproportionately high intake of omega 6’s biases our physiology towards thrombosis, hyperlipidemia, and vasoconstriction. The reverse of those effects occurs simply by increasing the proportion of omega-3’s.


Fish Oil as a Fat Loss Supplement?

 So far, the resume of fish oil’s health effects is very extensive. But can it add fat loss to the list as well? The buzz in the supplement industry would certainly want consumers to believe so. But as always, the answer can only begin to reveal itself in the research.

Human studies examining the effect of fish oil supplementation on body composition are scarce, but that makes it easy to pick them apart.

A decade ago, Couet and colleagues investigated the effect of replacing 6g of visible dietary fat with 6g of fish oil in healthy adults over a 3-week period, done 12 weeks after a 3-week control diet period [12]. Bodyfat mass and respiratory quotient decreased in the fish oil phase. It’s important to note that the flaws in this study’s design are grave enough to almost completely invalidate it. Extremely small sample size (6 subjects total), short trial period (3 weeks), and a complete absence of randomization or treatment balance (opening the distinct possibility for seasonal variation, among other errors) are the main fatal knocks that render this data nearly useless. In contrast, 2 more recent studies conducted within the past 3 years looking at weight-loss diets supplemented with omega-3’s have not observed any significant effects on body composition beyond what was caused by dietary restriction alone [13,14]. But it’s never that simple, since things may differ according to the population and protocol. In contrast to the previous two trials, Kunesova’s team examined the effects of omega-3 supplementation on severely obese female inpatients undergoing a 3-week very low calorie (525 kcal) in-patient weight reduction treatment [15]. Calories were controlled to accommodate the supplemental omega-3, which was 2.8g/day. Result?

The omega-3 supplemented group lost 1.5 kg bodyweight, and 2.2 cm more off the waist than the control group.

 How about more relevant populations? As of this writing, there are only three trials in existence examining the effect of omega-3 supplementation combined with a structured aerobic exercise program on body composition. Let’s dig in. In 1989, Warner and colleagues looked at the effect of walking or jogging 3 days/week for 45–50 minutes at 75-80% maximal heart rate in hyperlipidemic subjects randomly assigned to 1 of 4 groups: fish oil + exercise, fish oil alone, corn oil, or control [16].Body fat was reduced only in the fish oil + exercise group. These data are severely limited by the absence of an exercise-only control group, leaving a huge question mark open regarding the relative contribution of exercise to the bottom line result. A year later, Brilla and Landerholm conducted a well-designed study on healthy, previously sedentary men [17]. This trial did contain an exercise-only control group, and no effect of fish oil on body fat was observed. 

In the most recent fish oil + exercise study to date, Hill’s team examined the effect of fish oil supplementation (6g) on overweight hypertensive/hyperlipidemic subjects (24 men and 41 women) over a 12 week period [18]

 Exercise was 3 days/week walking at 75% predicted maximal heart rate for 45 minutes. Body composition was assessed by dual energy X-ray absorptiometry (DEXA). Predictably, fish oil supplementation improved blood lipids and arterial vasodilation. As for body composition, fish oil by itself didn’t cause any bodyfat reduction from baseline levels, whereas the sunflower oil control gained bodyfat , but to an insignificant degree. However, fish oil + exercise caused a 1.1% greater bodyfat reduction compared to the sunflower oil + exercise control (1.2% reduction versus a 0.1% reduction in the sunflower oil group). But here’s the kicker… The daily intake of the exercising fish oil group averaged 143.4 kcals less than the exercising control group. Factoring in the reduced calories of the fish oil group, we’re now looking at a difference of 0.32 kg (0.7 lb) — less than a pound more weight loss in the fish oil group in 12 weeks.

fish oil

The Dark Side of Over-doing Fish Oil Supplementation

Yes, Luke, there is always a dark side. In the world of unchecked marketing hype, fish oil has definitely gotten the “more is better” stamp. The problem is, EPA and DHA have a well-documented ability to suppress the body’s immune response. Although not as consistent as the immune effects, data also exist on the ability of EPA and DHA to increase bleeding time and oxidation. Let’s take a look at a couple of the published peer-reviewed research that no one in the fitness industry talks about. Thies and colleagues examined the 12-week effect of various fatty acid supplement mixes on healthy subjects [19]. Various blends of placebo oil and oils rich in ALA, GLA, AA, DHA, or EPA (720mg) + DHA (280mg) were compared. Total fat intake from the 9-capsule dose was 4 g/d.

The EPA/DHA treatment was the only one that had a negative effect on immunity, significantly decreasing natural killer cell activity by 48%. This effect was reversed after 4 weeks of ceasing intake of the supplement.

 Rees and colleagues investigated the effects of various amounts of EPA on immune markers in young and older men [20]. In a 12-week study, EPA was incorporated into plasma and mononuclear cell phospholipids. Supplemental EPA in amounts of 1.35, 2.7, and 4.05g/day caused a dose-dependent decrease in neutrophil respiratory burst, indicating the suppression of a cellular defense against immunity threats. This effect was seen in the older, but not the younger men.

Based on these and the previous data, if you’re not a spring chicken, and immunity is an issue, you might not want to go hog-wild on the fish oil dosing.


Suggested Use & Take-Home Tips

The cardio-protective benefits of increasing the dietary proportion of omega-3 fatty acids is seen consistently in trials involving various populations and protocols.

Fish oil is one of the few supplements that actually has a substantial body of scientific evidence backing it up.

However, it’s easy to think in terms of pills instead of food. Those who love fish (and have the time or resources to prepare or order it) can simply increase or maintain their intake of fatty fish such as salmon, mackerel, lake trout, herring, albacore tuna, and sardines. The American Heart Association (AHA) recommends at least two servings of fish per week for the general population. Think of a palm-sized piece as a serving. For those with high triacylglycerol levels, a supplemental 2-4g of combined EPA/DHA is their suggested therapeutic dose. However, note that caution is advised against supplementing more than 3g combined EPA/DHA outside of a physician’s care, since some individuals may risk excessive bleeding [21]. 3 g combined EPA/DHA typically is contained within 10 one-gram capsules.

I recommend maxing out your whole food options first before going the supplemental route.

There’s always more complete and synergistic nutrition contained within whole foods. Having 3-6 oz fatty fish a minimum of 4 times a week would exempt most healthy folks from needing fish oil supplementation. For those who can’t or won’t eat fish, there’s always fish oil capsules, which thankfully are inexpensive, and more convenient than getting your omega-3’s through fish. The amount of EPA/DHA per capsule may vary with the brand. Capsules can contain anywhere from 250-500mg. Most healthy folks don’t need more than 3-6 one-gram capsules per day to meet or exceed the amounts that show benefits. There are no definitive conclusions about optimal proportion of EPA:DHA, so to error on the side of safety, I recommend finding roughly an even mix. It’s common and perfectly acceptable for products to contain slightly more EPA than DHA. If at all possible, make sure your supplement is verified by the USP (United States Pharmacopoeia) for the peace of mind that you’re getting what the label is claiming. I would also error on the side of safety and keep them refrigerated. As a side note, there’s a widespread belief that ALA from flaxseed is worthless for increasing EPA/DHA since the conversion is inefficient. However, Harper’s team recently saw 3g ALA/day (from 5.2g flaxseed oil) raise plasma EPA levels by 60% at the end of a 12-week trial [22].

 Looking at the body of evidence as a whole, fish oil (or increased fish consumption) has great potential for improving cardiovascular health. But for reducing body fat, the effects are minor to nonexistent.

Let’s not forget that fish oil isn’t some magical negative-calorie food. It still contains 9 calories per gram, and no matter how much of those calories are used in its processing within the body, it’s still a net gain in calories after consumption. To sum everything up, fish oil has health benefits, as well as potential risks. It’s certainly not a matter of more-is-better. It might have minor fat loss effects in the obese and overweight population, but their fat loss effect in general is far from conclusively established. Get a variety of fats in your diet, and get them from whole foods whenever possible. Fish oil is merely one of many agents that can contribute to optimal health within the context of well-balanced nutrition. Keep it in perspective, and keep your eye on the facts.  

Author: Alan Aragon


  1. Centers for Disease Control: Behavioral Risk Factor Surveillance System. 1990-2002 trends data, nationwide.
  2. Thijssen MA, et al. Stearic, oleic, and linoleic acids have comparable effects on markers of thrombotic tendency in healthy human subjects. J Nutr. 2005 Dec;135(12):2805-11.
  3. Mozaffarian, et al. Trans fatty acids and cardiovascular disease. N. Engl. J. Med. 2006;354: 1601-1613.
  4. Lovejoy JC, et al. Effects of diets enriched in saturated (palmitic), monounsaturated (oleic), or trans (elaidic) fatty acids on insulin sensitivity and substrate oxidation in healthy adults. Diabetes Care. 2002 Aug;25(8):1283-8.
  5. Haalaininen E, et al. Diet and serum sex hormones in healthy men.
    J Steroid Biochem. 1984 Jan;20(1):459-64.
  6. Schwalfenberg G. Omega-3 fatty acids: their beneficial role in cardiovascular health.
    Can Fam Physician. 2006 Jun;52:734-40.
  7. Psota TL, et al. Dietary omega-3 fatty acid intake and cardiovascular risk.
    Am J Cardiol. 2006 Aug 21;98(4A):3i-18i.
  8. Ismail HM. The role of omega-3 fatty acids in cardiac protection: an overview.
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  9. Parker G, et al. Omega-3 fatty acids and mood disorders.
    Am J Psychiatry. 2006 Jun;163(6):969-78. Review. Erratum in: Am J Psychiatry. 2006 Oct;163(10):1842.
  10. Griel AE, et al. An increase in dietary n-3 fatty acids decreases a marker of bone resorption in humans. Nutr J. 2007 Jan 16;6:2.
  11. Simopolous AP. Omega-3 fatty acids in inflammation and autoimmune diseases. J Am Coll Nutr. 2002 Dec;21(6):495-505.
  12. Couet C, et al. Effect of dietary fish oil on body fat mass and basal fat oxidation in healthy adults. Int J Obes Relat Metab Disord. 1997 Aug;21(8):637-43.
  13. Fontani G, Corradeschi F, Felici A, et al. Blood profiles, body fat and mood state in healthy subjects on different diets supplemented with omega-3 polyunsaturated fatty acids. Eur J Clin Invest 2005;35:499–507.
  14. Krebs JD, et al. Additive benefits of long-chain n-3 polyunsaturated fatty acids and weight-loss in the management of cardiovascular disease risk in overweight hyperinsulinaemic women. Int J Obes (Lond). 2006 Oct;30(10):1535-44.
  15. Kunesova , et al. The influence of n-3 polyunsaturated fatty acids and very low calorie diet during a short-term weight reducing regimen on weight loss and serum fatty acid composition in severely obese women. Physiol Res. 2006;55(1):63-72
  16. Warner JG, et al. Combined effects of aerobic exercise and omega-3 fatty acids in hyperlipidemic persons. Med Sci Sports Exerc 1989;21:498–505.
  17. Brilla LR, Landerholm TE. Effect of fish oil supplementation and exercise on serum lipids and aerobic fitness. J Sports Med Phys Fitness 1990;30:173–80.
  18. Hill AM, et al. Combining fish-oil supplements with regular aerobic exercise improves body composition and cardiovascular disease risk factors.
    Am J Clin Nutr. 2007 May;85(5):1267-74.
  19. Thies F, et al. Dietary supplementation with eicosapentaenoic acid, but not with other longchain n-3 or n-6 polyunsaturated fatty acids, decreases natural killer cell activity in healthy subjects aged >55 y. Am J Clin Nutr. 2001 Mar;73(3):539-48.
  20. Rees D, et al. Dose-related effects of eicosapentaenoic acid on innate immune function in healthy humans: a comparison of young and older men. Am J Clin Nutr. 2006 Feb;83(2):187-8.
  21. Kris-Etherton PM, et. al. Fish consumption, fish oil, omega-3 fatty acids, and cardiovascular disease. Circulation. 2002 Nov 19;106(21):2747-57.
  22. Harper CR, et al. Flaxseed oil increases the plasma concentrations of cardioprotective (n-3) fatty acids in humans. J Nutr. 2006 Jan;136(1):83-7.


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