Fish oil contains both DHA and EPA. These are essential fatty acids for human health. They can be made from plant-based oils that contain alpha linolenic acid in foods such as nuts, flaxseeds, and leafy greens. But the conversion is not always easy to do in the human body. Evidence is accumulating supporting a better effect from DHA over EPA for cardiovascular protection. DHA is more effective at lowering blood pressure and improving endothelial function. It is more effective for raising HDL and decreasing platelet adhesion and aggregation. Both EPA and DHA decrease triglycerides (TG) by approximately 14-35% depending on the TG levels and dose of EPA/DHA used. Cholesterol comes in little particles called lipoproteins. Little ones cause problems, big ones are more protective and associated with less risk of stroke and heart attack. DHA is more effective for altering lipoprotein size because it is a more potent inhibitor of cholesterol ester transfer protein activity, an enzyme involved in lipoprotein particle size. In animal and human studies, DHA was more effective than EPA in reducing blood pressure. DHA was also shown to be able to lower heart rate whereas EPA was not able to do this.
Fish Oil and Trimethylamine N-oxide
Also of great interest to me is new research on the ability of fish oil to lower something called Trimethylamine N-oxide (TMAO). Interestingly, fish flesh contains TMAO, a dangerous compound associated with increased mortality from heart attack and stroke but the oil inhibits its production. TMAO is made through a three-step process. First, one must consume dietary choline, phosphatidylcholine or carnitine. Then the gut bacteria makes something called TMA which goes to the liver and is converted into TMAO. TMAO is closely linked to a number of problems including kidney disease, atherosclerosis and even heart failure. This is something I am particularly interested in. TMAO is inhibited by extra virgin olive oil and the red pigment in wine. Now we know that fish oil also inhibits TMAO. If one thinks about the heart healthy Mediterranean diet we immediately think of fish, red wine, and olive oil. Inhibition of TMAO may be one reason why this diet is associated with less cardiovascular mortality.
- Gao X, Xu J, Jiang C, et al. Fish oil ameliorates trimethylamine N-oxide-exacerbated glucose intolerance in high-fat diet-fed mice. Food Funct. 2015;6(4):1117-1125.
- He Z, Hao W, Kwek E, et al. Fish Oil Is More Potent than Flaxseed Oil in Modulating Gut Microbiota and Reducing Trimethylamine-N-oxide-Exacerbated Atherogenesis. J Agric Food Chem. 2019;67(49):13635-13647.