TL;DR

• Omega-3, 6 and 9 are all unsaturated fats, but not interchangeable. Omega-6 is generally abundant in modern diets, the body makes its own omega-9, and long-chain omega-3 (EPA and DHA) is the one that's genuinely harder to get enough of.
• Omega-3, specifically EPA and DHA, supports brain, eye and heart function, and helps regulate inflammation.
• DHA is a critical structural fatty acid for fetal brain and retinal development in pregnancy. In perimenopause and menopause, the evidence is more mixed, some support for mood, genuinely inconsistent results for hot flushes.
• Fish oil spoils through oxidation, triggered by heat, light and oxygen exposure. Oxidised oil is what actually causes that sharp, rancid fishy taste.
• IFOS provides independent, lot-specific testing for potency, contaminants and oxidation, with results available for certified batches.
• Fishy burps aren't always a sign of rancid oil, they often just come from the capsule releasing oil in the stomach. Oxidation makes the flavour far worse when it's present, but taste alone isn't a reliable freshness test.

Omega-3, 6 and 9: not interchangeable, not equally important

Omega-3, 6 and 9 are all unsaturated fats, but they aren't interchangeable. Omega-6 is generally abundant in modern diets, while the body can make omega-9 itself. Long-chain omega-3s EPA and DHA are harder to get enough of unless oily fish or other marine sources are eaten regularly. That's why omega-3, specifically two of its forms, EPA and DHA, is the one worth paying attention to.

What omega-3 actually does

EPA and DHA are structural components of cell membranes and play a role in regulating inflammation. DHA specifically is a major structural fat in the brain and retina, which is why it gets singled out in pregnancy and early development. EPA is more associated with inflammatory regulation and cardiovascular markers. Together, they're linked to heart, brain and eye health, though "linked to" is doing real work in that sentence, the strength of the evidence varies a lot depending on the specific outcome and population.

Pregnancy: the clearest case

DHA is a critical structural fatty acid for fetal brain and retinal development, and maternal DHA intake and status contribute to the DHA available for fetal accretion. This is the single strongest, most specific reason omega-3 shows up in prenatal formulations, not a general wellness claim, a structural one.

Perimenopause and menopause: more mixed

The picture here is genuinely less settled. Several smaller trials found omega-3 improved hot flush frequency, but the largest, most rigorous trial to date, a 12-week RCT in over 350 perimenopausal and postmenopausal women, found no significant difference from placebo. A broader systematic review reached a similar conclusion: no strong evidence for vasomotor symptoms, sleep or depression overall, though a few individual studies showed benefit for mood specifically. The honest summary is that omega-3 for menopausal symptoms is plausible and worth trying, not a proven fix.

What actually spoils an omega-3 supplement

Fish oil is unsaturated fat, which makes it inherently unstable. Exposure to heat, light and oxygen triggers oxidation, breaking the oil down and generating compounds responsible for rancid, fishy and metallic off-flavours. This happens gradually on the shelf and accelerates once a bottle is opened, which is why storage, packaging and how fresh the oil was to begin with all matter more than people assume.

What to actually look for when choosing one

• Form: triglyceride and re-esterified triglyceride forms can show better bioavailability than ethyl esters in some studies, and are closer to how omega-3 naturally occurs in fish, though absorption also depends on formulation and whether the supplement is taken with food.
• Freshness testing: oxidation is commonly assessed using peroxide value, anisidine value and TOTOX (total oxidation). Lower values generally indicate less oxidation, and publishing batch results provides far more useful information than simply claiming an oil is "fresh."
• Third-party testing: independent verification that a product actually contains what the label claims, and is free of contaminants at the levels tested.
• EPA:DHA ratio and dose: check how much EPA and DHA the product actually provides rather than relying on the total "fish oil" number. Different research questions and clinical contexts have used different EPA and DHA doses and proportions, in pregnancy specifically, DHA gets particular emphasis because of its structural role in fetal brain and retinal development.

What IFOS actually is

IFOS, the International Fish Oil Standards program, is an independent, batch-by-batch testing system, not a marketing badge a brand can just print on. Every certified lot is tested for potency (does it contain the EPA and DHA the label claims), purity (heavy metals like mercury and lead, PCBs, dioxins), and freshness (oxidation, via peroxide and TOTOX values), and results are published, not just pass or fail. A five-star rating means a specific batch cleared all of it. IFOS provides independent, lot-specific testing for some of the things that matter most in fish oil quality: label accuracy, contaminants and oxidation.

What actually causes fishy burps

Fishy burps aren't necessarily a sign that an oil has gone rancid, fish oil can produce an aftertaste or repeat simply because the capsule releases oil in the stomach rather than further down. Oxidation makes the problem far more noticeable, since oxidation products are behind many of the strong fishy, metallic and rancid flavours associated with deteriorating fish oil, but taste alone isn't a reliable freshness test on its own, which is exactly why objective oxidation testing matters more than how a product happens to taste on a given day. Taking fish oil with a meal may also improve tolerability for some people.

This article is for general educational purposes and isn't medical advice. Please consult a doctor or dietitian about your individual needs, particularly if you're pregnant, breastfeeding, or taking blood-thinning medication.

Sources

1. National Institutes of Health, Office of Dietary Supplements. Omega-3 Fatty Acids: Fact Sheet for Health Professionals. https://ods.od.nih.gov/factsheets/Omega3FattyAcids-HealthProfessional/

2. Cohen LS, et al. Efficacy of omega-3 for vasomotor symptoms treatment: a randomized controlled trial. Menopause, 2014;21(4):347-354. https://pubmed.ncbi.nlm.nih.gov/23982113/

3. Iqbal AZ, Wu SK, Zailani H, Chiu WC, Liu WC, Su KP, Lee SD. Effects of Omega-3 Polyunsaturated Fatty Acids Intake on Vasomotor Symptoms, Sleep Quality and Depression in Postmenopausal Women: A Systematic Review. Nutrients, 2023;15(19):4231. doi:10.3390/nu15194231. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10574492/

4. Minihane AM. Omega-3 fatty acids, brain health and the menopause. Post Reproductive Health, 2025;31(2):97-104. doi:10.1177/20533691251341701. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12209554/

5. IFOS (International Fish Oil Standards) Program, Nutrasource. https://nutrasource.ca/ifos/

6. Ghasemifard S, Turchini GM, Sinclair AJ. Omega-3 long chain fatty acid "bioavailability": a review of evidence and methodological considerations. Progress in Lipid Research, 2014;56:92-108. https://doi.org/10.1016/j.plipres.2014.09.001

7. Miyashita K, Uemura M, Hosokawa M. Effective Prevention of Oxidative Deterioration of Fish Oil: Focus on Flavor Deterioration. Annual Review of Food Science and Technology, 2018;9:209-226. doi:10.1146/annurev-food-030117-012320