Fish Oil on Effects on Body Composition & Fat Burning


by Monica Mollica

Here I will present the results of a more recent study that investigated the effects of fish oil supplementation on body composition and metabolic outcomes.[1]

The study

24 women – 66 years old – were randomly assigned to supplement with either 5 g fish oil – providing 2 g EPA and 1 g DHA per day – or a placebo (3 g olive oil, Swanson EFAs, Certified Organic Extra Virgin Olive Oil) for 12 weeks.

Exercise measurements were taken before and after 12 week of supplementation and resting metabolic measures were made before and at 6 and 12 week of supplementation. Subjects were instructed to keep their habitual dietary intakes and physical activity levels during the study period.

The results demonstrated that fish oil supplementation significantly increased resting metabolic rate by 14%, energy expenditure during exercise by 10%, and fat oxidation – i.e. “fat burning” – during rest by 19% and during exercise by 27%.

The 14% increase in resting metabolic rate translated into an increased energy expenditure of 187 calories per day.

In addition, fish oil supplementation reduced triglyceride levels (i.e. blood fats) by 29% and increased lean mass by 4% (3.53 lb or 1.6 kg) and functional capacity by 7% (measured by the “Timed Get Up and Go” [TUG] test). No changes occurred in the placebo group. There was also a small reduction in the inflammatory marker CPR (C-Reactive Protein) when compared to the placebo group.

It was concluded that fish oil supplementation may be a strategy to improve age-related physical and metabolic changes in healthy older females.


This study confirms findings from some earlier studies that I cited in my previous article “Fish Oil for Muscle Growth and Prevention of Muscle Loss with Aging”, which found increases in lean body mass (muscle mass), energy expenditure and fat burning.

Energy expenditure

While other studies suggested that the increase in resting metabolic rate is primarily due to the increase in lean body (muscle) mass, in this study the increase in energy expenditure at rest and during exercise remained significant even when normalized for body mass and lean mass, suggesting that the increase in lean mass was not the main factor influencing the increase in energy expenditure. A possible contribution to the elevation in energy expenditure could be that fish oil increases the activity of metabolic futile cycles, which are biochemical reaction that expend energy.[2-6] Another explanation – known as the pacemaker theory – suggests that an increase in cell membrane unsaturation results in an elevated metabolic rate by increasing membrane proteins and/or membrane associated processes.[7, 8]

Body fat

Despite the elevation in energy expenditure and fat burning, in this study there was no reduction on body fat.[1] This may be because of the short duration of 12 weeks (3 months) and/or because the subjects consumed a high-carb diet (50% carbs, 20% protein, 30% fat). Previous studies show that high-carb intakes [9, 10], as well as high intakes of omega-6 fats [11], may abrogate the fat loss effect of fish oil.

Lean (muscle) mass gain

The 4% (3.53 lb or 1.6 kg) increase in lean mass in just 3 months is impressive. It should be noted that this study used BIA (bioelectrical impedance) to analyze body composition. Ideally, a more precise measurement of body composition using DEXA (dual x-ray absorptiometry) or MRI (magnetic resonance imaging) should be used in studies investigating effects on interventions on body composition. DEXA and MRI can also show where on the body lean (muscle) is being gained. Nevertheless, a previous study reported a similar increase (3.5%) in thigh muscle lean mass using DEXA [12], indicating that this amount of gain in lean mass may be realistic, at least in this population.

Strength and physical function

Although this study did not find any significant increase in grip strength, a significant 7% increase in physical function, as determined by TUG speed, was demonstrated. It is notable that this was found without any exercise program.[1]

A previous study reported an increase in physical performance, as measured by walking speed, in response to supplementation with 1.2 g/d of EPA + DHA for 6 months in 126 frail older women aged 75 years.[13] In another study in 45 older women aged 64 years, fish oil supplementation (2 g/d) combined with a 90 d strength training protocol resulted in significant increases in functional capacity (sit to stand test), muscular strength, and neural activation (as measured by electromyography), which were greater than values achieved by strength training alone.[14]

A more recent study in 60 healthy 60-85 year old men and women reported an increase in handgrip strength by 2.3 kg, and an increase in 1-repetition maximum strength by 4% in response to fish oil supplementation (EPA: 1.86 g; DHA: 1.5 g) for 24 weeks.[15] It may be that the 12 week supplementation period in the study reported here was not long enough to evoke increases in strength.

One mechanisms by which fish oil improves physical and muscle function is by increasing the fluidity of the muscle membranes, as well as the sensitivity to acetylcholine [16], which is a neurotransmitter that evokes muscle contractions.

Triglycerides (blood fats) and Inflammation (CRP)

The reduction in triglycerides and CRP seen in this study are not surprising.[1] Fish oil is an effective “drug” for lowering triglycerides (it does so even better than the widely prescribed statin medications) [17, 18], and is well known for its anti-inflammatory effects.[19-22] However, to reduce CRP levels in apparently healthy people a higher dose (at least 3 g EPA + DHA) [1, 23] taken for a longer duration seems to be required, as previous studies providing a low dose fish oil (1.5 to 1.8 g EPA+DHA) [24-26] or being of short duration (less than 8 weeks) [27] did not show any reductions in CRP levels. Also, no reductions in CRP are seen in people with low baseline CRP levels, even at higher doses.[28]

However, the finding that supplementation with extra-virgin olive oil had no effects on inflammatory status (measured by CRP) may come as a surprise, considering that olive oil has well documented health benefits, some of which are related to its anti-inflammatory effects.[29-31] But the lack of effect of extra-virgin olive oil on CRP doesn’t mean it is worthless. For example, polyphenols in extra-virgin olive oil increase the anti-inflammatory effect of HDL (i.e. improves functionality of the “good cholesterol” [32] and decrease atherogenicity of LDL (i.e. make the “bad cholesterol” less bad).[33] Thus using extra-virgin olive oil for cooking is a good idea. Fish oil should not be used for cooking as that will damage (cause lipid peroxidation of) the perishable EPA and DHA fatty acids. If you want the best of both worlds, swallow your fish oil softgels or teaspoons and use extra-virgin olive oil for cooking.

Concluding reflections

Does fish oil increase lean (muscle) mass and strength in young men and women also?

There are currently no studies that have directly compared fish oil effects on body composition parameters in different age groups in the same study under the same conditions (dose, EPA:DHA ratio, duration etc). However, as I outlined in my previous articles, several studies have demonstrated that fish oil supplementation confers benefits for younger adults also in terms of fat loss and anabolic response of muscle protein synthesis to amino acids and insulin. Whether the latter translates into greater muscle mass and strength gains in young folks has not yet been investigated in any study. But considering that the acute response of net muscle protein balance reflects 24-hour balance after exercise and amino acid ingestion [34], and that the enhanced amino acid sensitivity of protein synthesis probably persists for just as long [35], the outlook for fish oil as a muscle anabolic enhancer for any gym rat – regardless of age – is promising.


Monica Mollica holds a Master degree in Nutrition from the University of Stockholm / Karolinska Institue, Sweden. She has also done PhD level course work at renowned Baylor University, TX. Having lost her father in a lifestyle-induced heart attack at an age of 48, she is a strong advocate of primary prevention and early intervention, and the development of lifestyle habits for health promotion at all ages. Today, Monica is sharing her solid medical research expertise and real-life hands-on-experience and passion for health and fitness by offering nutrition / supplementation / exercise / health consultation services, and working as a medical writer specializing in health promotion, fitness and anti-aging. She is currently in the process of writing a book on testosterone, covering health related issues for both men and women.

Website: www.Ageless.Fitness
Email: Monica@Ageless.Fitness


1. Logan, S.L. and L.L. Spriet, Omega-3 Fatty Acid Supplementation for 12 Weeks Increases Resting and Exercise Metabolic Rate in Healthy Community-Dwelling Older Females. PLoS One, 2015. 10(12): p. e0144828.
2. Qian, H. and D.A. Beard, Metabolic futile cycles and their functions: a systems analysis of energy and control. Syst Biol (Stevenage), 2006. 153(4): p. 192-200.
3. Guan, H.P., et al., A futile metabolic cycle activated in adipocytes by antidiabetic agents. Nat Med, 2002. 8(10): p. 1122-8.
4. Sridharan, G.V., et al., Discovery of substrate cycles in large scale metabolic networks using hierarchical modularity. BMC Syst Biol, 2015. 9: p. 5.
5. Stein, R.B. and J.J. Blum, On the analysis of futile cycles in metabolism. J Theor Biol, 1978. 72(3): p. 487-522.
6. Hue, L. and H.G. Hers, Utile and futile cycles in the liver. Biochem Biophys Res Commun, 1974. 58(3): p. 540-8.
7. Hulbert, A.J., et al., Dietary fats and membrane function: implications for metabolism and disease. Biol Rev Camb Philos Soc, 2005. 80(1): p. 155-69.
8. Hulbert, A.J., Membrane fatty acids as pacemakers of animal metabolism. Lipids, 2007. 42(9): p. 811-9.
9. Hao, Q., et al., High-glycemic index carbohydrates abrogate the antiobesity effect of fish oil in mice. Am J Physiol Endocrinol Metab, 2012. 302(9): p. E1097-112.
10. Ma, T., et al., Sucrose counteracts the anti-inflammatory effect of fish oil in adipose tissue and increases obesity development in mice. PLoS One, 2011. 6(6): p. e21647.
11. Madsen, L. and K. Kristiansen, Of mice and men: Factors abrogating the antiobesity effect of omega-3 fatty acids. Adipocyte, 2012. 1(3): p. 173-176.
12. Smith, G.I., et al., Fish oil-derived n-3 PUFA therapy increases muscle mass and function in healthy older adults. Am J Clin Nutr, 2015. 102(1): p. 115-22.
13. Hutchins-Wiese, H.L., et al., The impact of supplemental n-3 long chain polyunsaturated fatty acids and dietary antioxidants on physical performance in postmenopausal women. J Nutr Health Aging, 2013. 17(1): p. 76-80.
14. Rodacki, C.L., et al., Fish-oil supplementation enhances the effects of strength training in elderly women. Am J Clin Nutr, 2012. 95(2): p. 428-36.
15. Smith, G.I., et al., Fish oil-derived n-3 PUFA therapy increases muscle mass and function in healthy older adults. Am J Clin Nutr, 2015.
16. Patten, G.S., et al., Dietary fish oil increases acetylcholine- and eicosanoid-induced contractility of isolated rat ileum. J Nutr, 2002. 132(9): p. 2506-13.
17. Gotto, A.M. and J.A. Farmer, Lipid management and cardiovascular risk reduction, in Metabolic Risk for Cardiovascular Disease, R.H. Eckel, Editor. 2011, Blackwell Publilshing Ltd.: American Heart Association. p. 156-180.
18. Jacobson, T.A., et al., National lipid association recommendations for patient-centered management of dyslipidemia: part 1–full report. J Clin Lipidol, 2015. 9(2): p. 129-69.
19. de Roos, B., et al., Identification of potential serum biomarkers of inflammation and lipid modulation that are altered by fish oil supplementation in healthy volunteers. Proteomics, 2008. 8(10): p. 1965-74.
20. Ellulu, M.S., et al., Role of fish oil in human health and possible mechanism to reduce the inflammation. Inflammopharmacology, 2015. 23(2-3): p. 79-89.
21. Li, K., et al., Effect of marine-derived n-3 polyunsaturated fatty acids on C-reactive protein, interleukin 6 and tumor necrosis factor alpha: a meta-analysis. PLoS One, 2014. 9(2): p. e88103.
22. Myhrstad, M.C., et al., Effect of marine n-3 fatty acids on circulating inflammatory markers in healthy subjects and subjects with cardiovascular risk factors. Inflamm Res, 2011. 60(4): p. 309-19.
23. Ciubotaru, I., Y.S. Lee, and R.C. Wander, Dietary fish oil decreases C-reactive protein, interleukin-6, and triacylglycerol to HDL-cholesterol ratio in postmenopausal women on HRT. J Nutr Biochem, 2003. 14(9): p. 513-21.
24. Root, M., et al., A randomized trial of fish oil omega-3 fatty acids on arterial health, inflammation, and metabolic syndrome in a young healthy population. Nutr J, 2013. 12: p. 40.
25. Geelen, A., et al., Intake of n-3 fatty acids from fish does not lower serum concentrations of C-reactive protein in healthy subjects. Eur J Clin Nutr, 2004. 58(10): p. 1440-2.
26. Flock, M.R., et al., Effects of supplemental long-chain omega-3 fatty acids and erythrocyte membrane fatty acid content on circulating inflammatory markers in a randomized controlled trial of healthy adults. Prostaglandins Leukot Essent Fatty Acids, 2014. 91(4): p. 161-8.
27. Damsgaard, C.T., et al., Fish oil in combination with high or low intakes of linoleic acid lowers plasma triacylglycerols but does not affect other cardiovascular risk markers in healthy men. J Nutr, 2008. 138(6): p. 1061-6.
28. Madsen, T., et al., The effect of dietary n-3 fatty acids on serum concentrations of C-reactive protein: a dose-response study. Br J Nutr, 2003. 89(4): p. 517-22.
29. Martin-Pelaez, S., et al., Health effects of olive oil polyphenols: recent advances and possibilities for the use of health claims. Mol Nutr Food Res, 2013. 57(5): p. 760-71.
30. Ghanbari, R., et al., Valuable nutrients and functional bioactives in different parts of olive (Olea europaea L.)-a review. Int J Mol Sci, 2012. 13(3): p. 3291-340.
31. Servili, M., et al., Biological Activities of Phenolic Compounds of Extra Virgin Olive Oil. Antioxidants (Basel), 2013. 3(1): p. 1-23.
32. Loued, S., et al., Extra-virgin olive oil consumption reduces the age-related decrease in HDL and paraoxonase 1 anti-inflammatory activities. Br J Nutr, 2013. 110(7): p. 1272-84.
33. Hernaez, A., et al., Olive Oil Polyphenols Decrease LDL Concentrations and LDL Atherogenicity in Men in a Randomized Controlled Trial. J Nutr, 2015. 145(8): p. 1692-7.
34. Tipton, K.D., et al., Acute response of net muscle protein balance reflects 24-h balance after exercise and amino acid ingestion. Am J Physiol Endocrinol Metab, 2003. 284(1): p. E76-89.
35. Phillips, S.M., A brief review of critical processes in exercise-induced muscular hypertrophy. Sports Med, 2014. 44 Suppl 1: p. S71-7.