Fish Oil / Omega-3

Fish oil — the primary dietary source of the long-chain omega-3 fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) — is among the most studied supplements in modern nutritional medicine. Both fatty acids are conditionally essential: they can be synthesized from the short-chain omega-3 ALA (found in flaxseed, walnuts), but conversion efficiency is low (~5–10% for EPA, <1% for DHA). Dietary and supplemental intake from fatty fish or fish oil capsules remains the most reliable way to achieve meaningful tissue levels. The most consistent and well-established effect of EPA+DHA supplementation is reduction of fasting triglycerides. Multiple meta-analyses and large RCTs confirm a dose-dependent reduction of approximately 15–30% in adults with elevated baseline levels (Mozaffarian & Wu, 2011). This triglyceride-lowering effect has been recognized in clinical guidelines and is the basis for prescription omega-3 formulations (e.g., icosapentaenoic acid ethyl ester at 4g/day for hypertriglyceridemia). The picture for cardiovascular event prevention — the most clinically important question — is considerably more complicated. Early epidemiological enthusiasm was tempered by the 2012 JAMA meta-analysis (Rizos et al., n=68,680) which found no statistically significant reduction in all-cause mortality, cardiac death, myocardial infarction, or stroke with omega-3 supplementation. The 2019 VITAL trial (Manson et al., n=25,871) found no significant reduction in primary MACE with 1g/day fish oil (840mg EPA+DHA), though secondary analysis suggested possible MI reduction, especially in those eating less fish at baseline. Contrasting with these null or weak findings, the REDUCE-IT trial (Bhatt et al., 2019) found a dramatic 25% relative risk reduction with high-dose (4g/day) icosapentaenoic acid ethyl ester (Vascepa) — but the use of mineral oil as the placebo is a legitimate scientific controversy, as mineral oil may have raised LDL-C in controls and thereby inflated apparent benefit. For brain health and mood, the mechanistic rationale is compelling: DHA is a major structural component of neuronal membranes (~40% of brain polyunsaturated fatty acids), and EPA modulates neuroinflammatory signaling. Multiple meta-analyses of omega-3 supplementation for depression show a statistically significant but modest effect, particularly with EPA-dominant preparations (>60% EPA). However, most positive trials enrolled clinically depressed patients; evidence for mood or cognitive improvement in healthy, non-depressed adults is much weaker and inconsistent. Overall, fish oil has a favorable safety profile. Fishy aftertaste and GI discomfort are the most common side effects, partially mitigated by triglyceride-form products and enteric-coated capsules. High-dose supplementation (>3g/day EPA+DHA) can modestly elevate LDL-C in some individuals and may extend bleeding time, which is relevant for individuals on anticoagulants or scheduled for surgery.