Fish oil is most known for its beneficial cardiovascular and cardiac health effects, and continues to top the list of health promoting supplements. In 2004 FDA approved a prescription fish oil preparation for treatment of high blood triglycerides (hypertriglyceridemia) (1). Recently several studies have shown that fish oil also has other beneficial effects, which might appeal more to the younger crowd, 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 from 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 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 at least partly to the fat loss observed with fish oil supplementation. In another article "Fish Oil for Muscle Growth" I'm covering the anti-catabolic/muscle growth effects of fish oil in more detail.
Does it work in humans - 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…
Recently several studies have shown that fish oil also can help people to get in shape. In a landmark study in healthy young non-obese males, 6 g of fat from butter, olive oil, sunflower oil and peanut oil was replaced with 6 g fish oil (corresponding to 1,100 mg EPA and 700 mg DHA) per day (55). After 3 weeks the researchers noted a significantly increased resting fat burning (fat oxidation) and a 1.94 lb (0.88 kg) decrease in body fat (measured by the golden standard method DEXA). There was no change in body weight. This fat loss was seen despite that subjects were told not to change their usual exercise and food habits.
It has also been found that supplementing with fish oil for 3 weeks (1,100 g EPA and 700 g DHA daily) significantly decreases insulin levels and increases fat burning after consumption of carbohydrate rich meals (57). Supplementation with fish oil providing 2,400 mg EPA and 1,600 mg DHA for 3 weeks also boosts fat burning during jogging exercise (58).
Combined with exercise
Fish oil seems to be even more effective when combined with exercise. In obese men and women, the effects of the addition of 6 g of fish oil daily (providing 360 mg EPA and 1,560 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 (59). 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 body fat mass with 4.4 lb (2 kg) (59). The finding that
body weight and body fat percentage didn't change in the placebo group (which was put on the same exercise program but received 6 g sunflower oil instead of the fish oil) underscores the efficacy of fish oil for fat loss.
It is interesting that the fat loss seen in the fish oil - exercise group occurred even though the subjects did not change their usual food habits; they just added the fish oil supplement and exercise program to their regimen. 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 (which didn’t exercise). This is probably due to the very low dose of EPA. Most studies showing that fish oil increases fat loss have use fish oil products that provide 1.5-2 times more EPA than DHA, like Lean Lipid Complex does.
Combined with a calorie restricted diet
Fish oil supplementation can boost calorie restricted diets as well. This was found in a study that investigated the effect of including fish oil as part of an energy-restricted diet, on weight loss (60). Young obese adults were put on a calorie restricted diet (30 % less calories than their usual intake, about 600 calorie deficit), supplemented with 6 g fish oil providing 1,500 mg EPA + DHA, or placebo (sunflower oil capsules). It was found that the fish oil enriched diet resulted in 2.2 lb (1 kg) more weight loss and greater reductions in waist circumference after only 4 weeks, than the same diet without fish oil (60).
Combined with a calorie restricted diet and exercise program
In a study that tested the effect of adding 2,800 mg/day fish oil (EPA:DHA ratio 2:1) to a low-calorie diet combined with an exercise program, severely obese women (61). After 3 weeks the fish oil group lost 3.3 lb (1.5 kg) more weight and slashed almost 1 inch (2.3 cm) more fat from their hips, than the non-supplemented group.
While body fat changes were not reported, the researchers did find a greater increase in blood beta-hydroxybutyrate (a ketone body) in the fish oil supplemented group compared with control group, and interpreted this as providing evidence of greater fat oxidation in the fish oil group (61). These findings indicate that the addition of fish oil to a relatively short (3 week) weight loss program comprising severe caloric restriction and exercise, may increase fat oxidation and lead to greater improvement in body composition.
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 (62-65). 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.
As outlined above, 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. The majority of evidence thus supports fish oil's ability to shift fat metabolism away from storage towards burning of body fat, even in humans.
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 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 changes in body composition. After all, it's not weight loss per see, but fat loss and muscle gain that's interesting from both a health, esthetic and physical performance viewpoint. I cover the muscle growth stimulating and anti-catabolic effect of fish oil in another article "Fish Oil for Muscle Growth".
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 (66); 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.
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