Fish oil and its omega-3 fats (EPA, DHA) are marketed as protective, but regulators approved them without evaluating their antithyroid, immunosuppressive, and antimitochondrial effects.[1] He grouped the fish-oil promotion campaign with earlier "radiation is good for you" and "estrogen prevents everything" cycles: an industry-favorable conclusion given decades before the toxic evidence caught up.[2]

Oxidation and PUFA toxicity

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Fish oils are extremely unstable and begin oxidizing before they reach the bloodstream; some of their apparent anti-inflammatory benefit comes from this oxidation, not from the intact oil.[3] Like other PUFA, EPA and DHA break down into acrolein, malondialdehyde, and other reactive products that poison the respiratory enzyme cytochrome oxidase and accelerate formation of the age pigment lipofuscin.[4]

Their "deficiency" in the tissues frequently corresponds to the intensity of oxidative stress and lipid peroxidation; it is usually their presence, rather than their deficiency, that created the disposition for the disease.

— Ray Peat[5]

Immune and cardiovascular claims

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In a meta-analysis of 11 randomized trials with 120,643 patients, omega-3 supplements did not raise overall bleeding, hemorrhagic stroke, intracranial, or gastrointestinal bleeding.[6]

A UK Biobank prospective cohort of 415,737 people (median 11.9 years follow-up) found regular fish-oil-supplement use raised the risk of first developing atrial fibrillation or stroke among initially healthy people, though it was associated with slower progression from atrial fibrillation to major cardiovascular events or death once disease was already present.[7] Fish oil's cholesterol- and triglyceride-lowering effect is attributed to liver toxicity rather than a genuine cardioprotective mechanism, and large cohort studies found no reduction in depression, suicide, or coronary heart disease from omega-3 intake.[8] Fish oil is markedly immunosuppressive, decreasing natural killer cell activity and worsening outcomes in animal infection studies, an effect exploited deliberately in transplant medicine to blunt organ rejection.[9]

Fish oils are much more immunosuppressive than seed oils, and among their early effects is suppressed prostaglandin synthesis.[10] A large amount of cod liver oil in dogs' diet raised their cancer death rate.[11]

Cod liver oil differs from other fish oils because it supplies vitamin A and vitamin D, useful where other sources are lacking, as in dark Norwegian winters; a fish-oil-derived A and D with most of the oil removed is preferable.[12][13]

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PUFA-derived acrolein glycates lysine in plaque-forming proteins, the basis for Ray Peat's link between fish-oil-associated lipid peroxidation and both Alzheimer's disease and prion diseases such as mad cow disease, which involve lipase activation and PUFA release.[14]


In the injured brain, DHA and arachidonic acid add to edema, weaken the blood-brain barrier and increase protein breakdown, inflammation and peroxidation, while the same amount of stearic acid causes no harm.[15]

Other marine n-3 products

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Krill oil and algae oil are marketed as alternatives to standard fish-oil capsules (phospholipid form, vegan DHA/EPA). They remain highly unsaturated marine-type fats with the same oxidation and antithyroid concerns as other long-chain omega-3 products. See above; they are not a separate metabolic category.

See also

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References

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  1. ↑ "The Great Fish Oil Experiment," Ray Peat article
  2. ↑ "The Great Fish Oil Experiment," Ray Peat article
  3. ↑ "The Great Fish Oil Experiment," Ray Peat article
  4. ↑ "The Great Fish Oil Experiment," Ray Peat article
  5. ↑ "The Great Fish Oil Experiment," Ray Peat article
  6. ↑ Javaid M, Kadhim K, Bawamia B, et al. "Bleeding risk in patients receiving omega-3 polyunsaturated fatty acids: a systematic review and meta-analysis of randomized clinical trials," J Am Heart Assoc. 2024;13(10):e032390. doi:10.1161/JAHA.123.032390. PMID 38742535. RR 1.09, 95% CI 0.91-1.31.
  7. ↑ Chen G, Qian ZM, Zhang J, et al. "Regular use of fish oil supplements and course of cardiovascular diseases: prospective cohort study," BMJ Med. 2024;3(1):e000451. HR 1.13 (AF), 1.05 (stroke), 0.92 (AF to MACE), 0.91 (death).
  8. ↑ "The Great Fish Oil Experiment," Ray Peat article
  9. ↑ "The Great Fish Oil Experiment," Ray Peat article
  10. ↑ Ray Peat, "The great fish oil experiment," raypeat.com.
  11. ↑ Ray Peat, "Unsaturated vegetable oils: toxic," raypeat.com. "...increased their death rate from cancer by 20 times, from the usual 5% to 100%."
  12. ↑ Ray Peat, "Jodellefit: Insulin Resistance, Vegans, Low Cortisol, Bone Broth, and Coconut", Jodellefit, 38:13
  13. ↑ Ray Peat, "COVID-19, Vaccines, Conspiracy Theories & Your Health Questions Answered", One Radio Network, 1:01:21
  14. ↑ "The Great Fish Oil Experiment," Ray Peat article
  15. ↑ Ray Peat, "Fats, functions and malfunctions," raypeat.com.