A 2015 study found that 83% of fish oil supplements sold in New Zealand exceeded recommended oxidation thresholds. Knowing how to evaluate freshness, form, and potency is essential before buying any omega-3 supplement.
For educational purposes only — not medical advice. How we evaluate evidence →
Written by
Coeheal Editorial Team
Coeheal Editorial Team
Reviewed by
Coeheal Editorial Team
Editorially reviewed for accuracy against cited sources. This is an editorial review, not a medical or clinical review. For personalised health advice, consult a qualified healthcare professional.
Last reviewed
This article is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before making health decisions. Our editorial standards →
ALA (from flaxseed, chia, walnuts) converts to EPA at only 5-10% efficiency and to DHA at less than 1%. EPA is the primary precursor to anti-inflammatory resolvins and protectins, most relevant for cardiovascular health and depression. DHA is the primary structural fatty acid in the brain (40% of brain PUFAs) and retina, critical for cognitive function and neurological development. The therapeutic dose for most conditions is 2-4 g/day of combined EPA+DHA. A 2019 meta-analysis of 13 RCTs found omega-3 supplementation reduced cardiovascular events by 8% and cardiovascular death by 7%.
Natural triglyceride (TG) form: omega-3s attached to a glycerol backbone as in fish; 70% better bioavailability than ethyl ester in some studies; more stable; more expensive. Ethyl ester (EE) form: produced by reacting fish oil with ethanol to concentrate EPA/DHA; lower bioavailability especially without fat; more prone to oxidation; cheaper and more common in mass-market supplements. Re-esterified triglyceride (rTG): EE converted back to TG form; similar bioavailability to natural TG. Phospholipid form (krill oil): omega-3 bound to phospholipids; may have better brain uptake; contains astaxanthin (antioxidant); but contains less EPA+DHA per gram than concentrated fish oil. Algae oil: the original marine omega-3 source; suitable for vegans; typically DHA-dominant; no heavy metal concerns.
TOTOX (Total Oxidation Value) = (2 x Peroxide Value) + Anisidine Value. GOED voluntary quality standards: Peroxide value 5 mEq/kg or less; Anisidine value 20 or less; TOTOX 26 or less. A 2015 study of 47 New Zealand fish oil supplements found 83% exceeded the recommended TOTOX threshold. Oxidised fish oil generates cytotoxic aldehydes (4-HNE, malondialdehyde) that may increase cardiovascular risk. How to assess: look for brands that publish TOTOX values; target TOTOX below 10 (excellent), below 16 (good), below 26 (acceptable). Sensory test: fresh fish oil should smell mildly oceanic; rancid oil smells strongly of fish, paint, or chemicals.
Most fish oil is made from small pelagic fish (sardines, anchovies, mackerel, herring) which accumulate fewer contaminants than large fish. Molecular distillation removes most heavy metals and PCBs - but quality varies. Third-party certifications: IFOS (International Fish Oil Standards) - the most rigorous; tests TOTOX, heavy metals, PCBs, dioxins; publishes results online. NSF International and ConsumerLab.com also test fish oils. Wild-caught fish from cold, clean waters (Norway, Peru, Alaska, Iceland) generally have lower contaminant levels.
Therapeutic dosing: cardiovascular health and triglyceride reduction 2-4 g/day EPA+DHA; depression 1-2 g/day EPA-dominant (EPA:DHA at least 2:1); general anti-inflammatory support 1-2 g/day. A standard 1,000 mg capsule contains only 300 mg EPA+DHA - concentrated supplements (500-800 mg per capsule) are more practical. Storage: refrigerate after opening; use within 3 months; keep away from heat and light. Take with a fat-containing meal for best absorption. Reliable brands: Nordic Naturals (IFOS certified, TG form, publishes TOTOX); Carlson Labs (IFOS certified); Thorne Research (pharmaceutical-grade, third-party tested); Wiley's Finest (wild Alaskan, IFOS certified). Vegan options: Testa Omega-3, Nordic Naturals Algae Omega, Ovega-3.
Personalised plan
Get a personalised natural weight loss and nutrition plan.
Seen a claim you want to verify?
The Claim Decoder grades the evidence behind any natural health claim — A to F, with sources.
Suggested from this article:
"Eating a Mediterranean diet reduces the risk of heart disease"
Prompted by: How to Choose a Fish Oil Supplement: EPA, DHA, TOTOX, and What to Look For
Intermittent and extended fasting activate pathways involved in autophagy — your body's built-in cellular cleanup system. The timing and clinical significance in humans are still being established. Here's what the science and tradition both say.
Not all supplements are created equal. These seven earth-grown herbs have centuries of traditional use and modern research behind them.
Type 2 diabetes is largely a lifestyle disease — and lifestyle medicine offers the most powerful tools for reversing it. Here's the evidence.
