Fish oil is well known for its beneficial cardiovascular and cardiac health effects. In 2004 FDA approved a prescription fish oil preparation for treatment of high blood triglycerides (hypertriglyceridemia) (1). However, recently several studies have shown that fish oil also has other beneficial effects, which might appeal more to the younger population, and especially to fitness and bodybuilding enthusiasts. One of these effects is fat loss.
Fish Oil Induced Fat Loss
In the 80s early 90s, several animal studies showed that fish oil reduces body fat (2-5) and weight gain (6-9), and limits adipose tissue expansion (10-12). These effects have been seen during both a decreased (3 7), constant (5) or even increased energy intakes (6). This indicates that the fatty acids in fish oil, notably EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), have an effect on the partitioning of fat between oxidation (fat burning) and storage in the body.
Mechanism – how does it work?
In search for the mechanisms behind fish oil induced fat loss, it has been found that fish oil exerts favorable metabolic effects by modulating gene expression (which is the process by which the information encoded in a gene is converted into protein) (2 13-26). While we inherit our genes (or blueprints) from our parents, what determines the way in which our blueprints are interpreted is largely dictated by a collection of environmental factors. The nutrients we consume are among the most influential of these environmental factors 27 28. One dietary constituent that has a strong influence on our genetic makeup is dietary fat (2 13 14 16-19 21-23 25 29). Fatty acids of dietary fat not only influences hormonal signaling events, but also have a very strong direct influence on the molecular events that govern gene expression. More specifically, it has been shown that the fatty acids EPA and DHA from fish oil (by affecting gene expression) inhibit the activities of fat synthesizing (lipogenic) enzymes (30-37), while at the same time stimulating the activities of key enzymes that govern fat oxidation (fat burning) (2 38-46).
Fish oil also has been shown to increase levels of adiponectin and decrease levels of cortisol (47 48). Adiponectin is a novel adipose tissue-specific protein that circulates in human plasma at high levels (49). It is one of the physiologically active polypeptides secreted by adipose tissue, whose multiple functions have started to be understood in the last few years. Some of its beneficial effects are enhanced insulin sensitivity, and lowered plasma glucose (blood sugar) and triglyceride levels (49 50). A reduction in adiponectin expression is associated with insulin resistance (49), and adiponectin levels are inversely related to the degree of adiposity (50). The activity of adiponectin has also been associated with steroid and thyroid hormones, glucocorticoids, and nitric oxide, and has anti-atherogenic and anti-inflammatory properties (50). Thus, it is plausible that fish oil induces some of its effect by affecting adiponectin levels. While the functions of adiponectin are just starting to emerge, it is likely to become a target for therapeutic applications in the future.
It is also interesting that fish oil lowers cortisol. While the exact role of cortisol in obesity isn’t fully elucidated (51 52), it is known that excessive cortisol levels result in substantial fat mass gain (53 54). Thus, the reduction in cortisol levels after fish oil supplementation could contribute to the fat loss effect of fish oil.
What’s in it for me?
At this point you might be thinking “ok, that all sounds nice, but I’m not a rat. Does it work in humans”?
Yes! Read on…
In a landmark study, healthy male participants were given a diet where 6 g of fat from butter, olive oil, sunflower oil and peanut oil was replaced with 6 g fish oil (corresponding to 1.1 g EPA and 0.7 g DHA) per day (55). After 3 weeks the researchers noted a significant increase in resting fat oxidation (fat burning) and a 1.94 lb (0.88 kg) decrease in body fat (measured by DEXA), in the face of a constant energy intake. Since there was no change in body weight, this implies that the fish oil supplement increased lean body mass (more on that in an upcoming article). This effect was seen despite the fact that the subjects were told not to change their usual exercise and diet habits.
Another study confirmed the ability of fish oil supplementation to increase fat oxidation (fat burning) during exercise (56). In this study, recreationally active men were given a daily fish oil supplement corresponding to 2400 mg EPA and 1600 mg DHA for 3 weeks. At the end of the study subjects performed a 60 min jogging exercise bout at 60% of VO2max, during which fat metabolism was measured. It was shown that the fish oil supplementation significantly increased the oxidation of fat for energy (e.g. fat burning) during the exercise session (56). It has also been shown that supplementing with fish oil for 3 weeks (1.1 g EPA and 0.7 g DHA daily) significantly decreases insulin levels and increases fat oxidation (fat burning) by 35% (!) after consumption of carbohydrate rich meals (57).
Recently, more studies have been published on the topic. In overweight men and women, the effects of the addition of 6 g of fish oil daily (corresponding to 360 mg EPA and 1560 mg DHA) in combination with regular aerobic activity (walking 45 min three times per week at an intensity of 75% of age-predicted maximal heart rate) for 12 weeks, was investigated (58).
The results showed that the combination of fish oil and regular aerobic activity not only improved several risk factors for cardiovascular disease, but also significantly reduced the amount of body fat (58). It is interesting that these effects were noted even though the subjects did not change their usual food habits other than adding the fish oil supplement. This indicates the great potential benefits of fish oil combined with regular physical activity for improving body composition and cardiovascular health. In this study, no fat loss was seen in fish oil only group (that didn’t exercise). This could be due to the older age of the subjects (47-51 yrs) in this study compared to the previous studies, and the relatively low dose of EPA. Fish oil supplementation has also been shown to result in a 2.22 lb (1 kg) greater weight loss after 4 weeks of dieting (reduced caloric intake) (59).
Perspective on fish oil and fat loss
In contrast to the positive studies, there are a few that didn’t show any fat loss with fish oil supplementation (60-63). This could be due to differences in subject characteristics (age, initial body fat mass, baseline physical activity), methodological differences, and differences in fish oil preparations (see below). However, several high quality studies have shown that fish oil supplementation has a significant fat loss effect in addition to all its other health promoting effects. Overall, fish oil seems to have the ability to shift fat metabolism away from storage toward burning of body fat.
It’s getting better – fat loss combined with lean mass (muscle) gain
In one of the most recent studies on fish oil’s fat loss effect, men and women (mean age 33 yrs) where given 4 g of fish oil corresponding to 1600 mg EPA and 800 mg DHA (48). After for 6 weeks, the placebo group, which was given 4 g of safflower oil, showed a tendency towards fat gain.
The fish oil group instead had lost 0.5 kg of fat mass and gained 0.5 kg of lean mass, with no change in body weight. This is a very beneficial body composition effect and underscores the importance of investigating fat mass and lean mass separately, since just measuring body weight will not tell anything about potential compositional changes, which after all is what is interesting from both a health, esthetic and physical performance viewpoint. I will cover the anti-catabolic and potential lean mass gaining effects of fish oil in more detail in an upcoming article.
Whether you are on a diet or not, adding a fish oil supplement to your regimen can effectively help you get in shape. The additional calories from the fish oil will not get stored (64); quite to the contrary, fish oil will help you get rid of calories you already have stored in your body fat. What’s interesting is that fish oil supplementation seems to reduce body fat and waist circumference despite unchanged exercise and/or other dietary practices.
Aim for a daily fish oil intake that provides you with at least 1600 mg EPA and 800 mg DHA, but a higher dose, 2400 mg EPA and 1600 mg DHA (a total of 4 g EPA and DHA total), might result in a larger fat loss. To achieve this high intake of EPA and DHA it is advisable to take a fish oil concentrate. In an upcoming article I will go into more detail about fish oil concentrates, different ratios of EPA to DHA in fish oil preparations, their relative effectiveness, safety aspects of high dose fish oil supplementation, and sort through the myriad of fish oil supplements currently available on the market, to help you find a good fish oil supplement that will give you the best bang and effectiveness for your buck.
About the Author
Monica Mollica holds a Master Degree in Nutrition from the University of Stockholm and Karolinska Institue, Sweden. She has also done PhD level course work at renowned Baylor University, TX.
Monica is a medical writer and clinical website developer. Being a fitness athlete herself, she is also sharing her hands-on experience by offering nutrition & health consultations, and body transformation coaching.
Having lost her father in a lifestyle-induced sudden heart attack at an age of 48, she is very passionate about health promotion and specializes in preventive medicine.
Monica is currently in the process of writing a book on testosterone, covering health related issues for both men and women. You can visit her website at www.Lean.Fitness.
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