The Short Answer
Fish oil is a source of omega-3. Omega-3 fatty acids (EPA and DHA) are the active ingredients. Fish oil is the most common supplement form that delivers them. Other sources include algal oil (vegan), krill oil, and cod liver oil.
| Term | What It Is | Contains |
|---|---|---|
| Omega-3 | A family of polyunsaturated fatty acids | EPA, DHA, ALA (from plants) |
| Fish Oil | Oil extracted from fatty fish (salmon, mackerel, sardine) | EPA + DHA (the two that matter for health) |
| Algal Oil | Vegan omega-3 source from microalgae | Primarily DHA, some EPA |
| Krill Oil | Oil from krill (tiny crustaceans) | EPA + DHA in phospholipid form |
| ALA (flax, chia, walnuts) | Plant-based omega-3 | ALA — poorly converted to EPA/DHA (<5%) |
EPA vs DHA: Does the Ratio Matter?
A 2025 network meta-analysis of 26 RCTs (1,892 participants) found that DHA+EPA combined significantly outperformed EPA alone for body weight and BMI outcomes. EPA alone showed no advantage over the combination.[1]
For specific outcomes, the research suggests different ratios may be optimal:
- Anxiety: EPA appears more important — a meta-analysis found greater effects with EPA-dominant formulations[3]
- Triglycerides: High-dose combined EPA+DHA reduces triglycerides by -50 to -57 mg/dL[2]
- General health: Combined DHA+EPA is the best-supported approach
What to Look for on the Label
The total fish oil dose is NOT the omega-3 dose. A "1,000 mg fish oil" capsule typically contains only 300 mg of combined EPA+DHA. Look for:
- Total EPA+DHA per serving — this is what matters, not total fish oil
- 2,000+ mg EPA+DHA/day for therapeutic doses (anxiety, triglycerides)
- Triglyceride form is better absorbed than ethyl ester form
- Third-party testing for heavy metals (mercury, PCBs) and oxidation
The Bottom Line
Fish oil and omega-3 are not alternatives — fish oil is simply the most common way to get omega-3 (EPA+DHA). The research supports combined DHA+EPA formulations over EPA-only. For most health outcomes, aim for 2+ g/day of total EPA+DHA, not total fish oil.
References
- Lu H, et al. "EPA vs DHA+EPA: network meta-analysis." Support Care Cancer. 2025. 26 RCTs, 1,892 participants. PubMed
- Basirat A, Merino-Torres JF. "Marine omega-3 and metabolic syndrome: meta-analysis." Nutrients. 2025. 21 RCTs. PubMed
- Su KP, et al. "Omega-3 and anxiety: JAMA meta-analysis." JAMA Netw Open. 2018. PubMed