High-fat diets are typically associated with gains in body fat, essentially because of the higher caloric density of fat. However, studies have shown that diets rich in omega-3 fatty acids found in fish oil, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), can actually reduce body fat.^1-3 Both of these fatty acids are polyunsaturated fatty acids that contain a carboxylic acid group attached to a rather long chain of covalently linked carbon atoms. As polyunsaturated fats, they also have several double bonds within their carbon chain, which significantly alters their chemical structure relative to other dietary fats such as saturated and monounsaturated fatty acids. The difference in chemical structure gives omega-3 fatty acids, like EPA and DHA, the unique capacity to reduce body fat while also decreasing inflammation— which together contribute to the many health benefits linked with their consumption, such as a lower risk for heart disease as well as certain cancers.^4,5

Although the precise mechanisms responsible for these effects are not completely understood, there are several possible explanations. To begin with, EPA and DHA burn fat by increasing the level and activity of mitochondria within the cell, resulting in greater fatty acid oxidation. Omega-3 fatty acids also minimize body fat by stimulating thermogenesis, which not only oxidizes body fat but also increases energy expenditure, further contributing to the reduction in body fat.

The anti-inflammatory effects associated with omega-3 fatty acids come from their ability to reduce the production of pro-inflammatory molecules known as prostaglandins⁶, by directly inhibiting the key enzyme involved in prostaglandin biosynthesis.⁷ In addition, the ability of omega-3 fatty acids to reduce body fat by increasing fatty acid oxidation and thermogenesis also contributes to their capacity to reduce the inflammatory response, as a loss of body fat actually reduces both the size and biochemical activity of fat cells. The diminished biochemical function of these fat cells actually depresses their release of pro-inflammatory cytokines, such as TNF-alpha, ultimately diminishing inflammation. The anti-inflammatory effects of omega-3 fatty acids have also been shown to increase insulin sensitivity, imparting a more anabolic environment that positively influences muscle growth.

Burn Fat and Sugar

Omega-3 fatty acids are one of the most common dietary supplements. This is mainly because of their proficiency at cutting body fat that is accomplished, in part, by increasing the expression of certain genes that increase the biosynthesis of the fat-torching subcellular organelle, the mitochondria.⁸ The PGC-1 alpha gene is one of the genes turned on by omega-3 intake that cranks up mitochondrial biosynthesis.⁹ Because the mitochondria are the power-producing organelles within the cell that burn fat for energy, the increase in mitochondria from omega-3 fatty acid consumption increases the capacity to oxidize fat and promote fat loss.

The use of omega-3 fatty acids has also been shown to boost the rate at which glucose is burned within muscle cells by stimulating glycolysis.⁸ Interestingly, the increase in glycolysis promoted greater levels of glucose uptake within the muscle cell by increasing the amount of the glucose transporter GLUT4 in the muscle cell membrane. The greater amount of GLUT4 transporters in the muscle cell membranes likely contributes to the ability of omega-3 fatty acids to enhance insulin signaling, as greater levels of GLUT4 in the muscle cell membrane will facilitate glucose transport into the muscle cell, reducing the amount of insulin required to shuttle glucose into the cell. The lower requirement for insulin will enhance insulin signaling by minimizing the negative feedback mechanisms that typically inhibit insulin signaling in response to excessive insulin levels.

Enhance the Anabolic Effect of Insulin

The ability of omega-3 fatty acids to improve insulin-mediated glucose metabolism means that omega-3s should also be able to boost insulin-triggered muscle protein synthesis, and therefore muscle growth. In order to verify this effect, a study by Gingras et al.¹⁰ looked at the impact of omega-3 fats on muscle protein synthesis in response to insulin. In this study, they showed that long-chain omega-3 fatty acids function as specific activators of mTOR and muscle protein synthesis by way of the insulin-signaling pathway. They also demonstrated that long-chain omega-3 fatty acids enhance the insulin-mTOR-protein synthesis-signaling pathway by diminishing whole-body inflammation, which has been shown to cause insulin insensitivity. Furthermore, they show that consumption of long-chain omega-3 fatty acids produced an increase in amino acid incorporation into muscle protein synthesis by 108 percent.

Anti-catabolic Effect Prevents Muscle Loss

In addition to their anabolic influence, omega-3 fats can also have a strong anti-catabolic effect by blocking the muscle-depleting influence of cortisol. The hormone cortisol is a steroid hormone that is normally released by the adrenal glands in response to stressful events such as caloric restriction. A few of its primary functions include increasing blood sugar and assisting in the metabolism of fats, carbohydrates and proteins.^11,12

Most caloric-restrictive diets lower carbohydrate consumption. When carbohydrate consumption is decreased from dieting, cortisol acts to reestablish glucose levels by converting non-carbohydrate fuel sources such as fatty acids and amino acids into glucose, a process known as gluconeogenesis. This cortisol-driven function consumes the immediately available stockpile of amino acids, causing the body to break down muscle tissue into amino acids for energy. Although cortisol release cannot be prevented, it can be controlled. Regulating the release of cortisol can be achieved by a diet rich in the EPA and DHA, as a study by Noreen et al.¹³ showed that six weeks of supplementation with 1,600 milligrams of EPA and 800 milligrams of DHA per day significantly preserved lean mass and decreased fat mass. These changes correlated with a reduction in salivary cortisol levels, demonstrating that these fatty acids lowered cortisol while preventing the loss of muscle mass.

Thermogenic-Driven Fat Loss and Increased Metabolic Rate

Thermogenesis occurs when the production of cellular energy, in the form of ATP, is uncoupled with fatty acid oxidation. As a result, instead of the energy from fat being used to synthesize ATP, it is instead converted into heat— which effectively increases energy expenditure, contributing to a higher metabolic rate that facilitates the ability to lose weight. Brown adipose tissue (BAT) is the most thermogenic tissue in the body because it is loaded with the uncoupling protein-1 (UCP-1) that can directly uncouple fat oxidation with ATP production driving thermogenesis. Omega-3 fatty acids trigger thermogenesis, in large part, by increasing the amount of BAT. This effect was shown in a study by Oudart et al.¹⁴ where researchers fed rats a high-fat diet with and without the omega-3 fatty acids EPA and DHA for four weeks. The group ingesting EPA and DHA showed an increase in thermogenic-activity that corresponded to an increase in the mass of their BAT, indicating that omega-3 intake increases the production of BAT-boosting thermogenesis.

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For most of Michael Rudolph’s career he has been engrossed in the exercise world as either an athlete (he played college football at Hofstra University), personal trainer or as a research scientist (he earned a B.Sc. in Exercise Science at Hofstra University and a Ph.D. in Biochemistry and Molecular Biology from Stony Brook University). After earning his Ph.D., Michael investigated the molecular biology of exercise as a fellow at Harvard Medical School and Columbia University for over eight years. That research contributed seminally to understanding the function of the incredibly important cellular energy sensor AMPK— leading to numerous publications in peer-reviewed journals including the journal Nature. Michael is currently a scientist working at the New York Structural Biology Center doing contract work for the Department of Defense on a project involving national security.

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