Full mechanism, in text

Choosing a form and checking freshness

1 · Three forms

Fish oil on the market comes in three chemical skeletons, (TG), ethyl ester (EE) and phospholipid (PL), and the skeleton sets absorption efficiency and price."Fish oil" is not one thing — omega-3 oils on the market come in three completely different chemical skeletons, which determine absorption efficiency and price:

· / rTG (natural triglyceride) — the original form inside fish. One glycerol + three fatty acids. rTG = re-esterified: first purified to high-concentration EE, then enzymatically packed back into a TG skeleton — higher cost but preserves the natural structure.
· EE (ethyl ester) — the most common form from industrial distillation purification. Glycerol is replaced by ethanol — cheap, but pancreatic lipase hydrolyzes it slowly. Vascepa (icosapent ethyl) + most cheap fish oils are EE.
· PL (phospholipid) — mainly from krill oil. / hangs directly off the phospholipid head — theoretically the best absorption, but EPA + DHA content per capsule is low and the price is highest.

Next step: what happens after they enter the small intestine.

2 · Lipase + bile · absorption gap

In the small intestine, pancreatic lipase must cut fatty acids off the skeleton, and it cuts ethyl esters slower than , so EE relies more on a fatty meal.After entering the small intestine, pancreatic lipase must first cleave the fatty acids off the skeleton before enterocytes can absorb them:

· → free FA: pancreatic lipase's natural substrate, helped by bile-acid emulsification
· EE → free FA: pancreatic lipase cleaves ethyl esters more slowly than triglycerides, so EE depends more on being taken with a meal that contains fat. Dyerberg 2010 (72 people, 3.3 g a day) compared relative bioavailability: with natural fish oil as 100%, re-esterified triglyceride (rTG) was 124% and ethyl ester (EE) 73%
· PL → free FA: / bonded to phospholipids is released by a different enzyme (phospholipase A2), and part can skip hydrolysis via a "lymph-priority" route

Practical implications:

· Read the bottle label — is it TG or EE
· Take EE fish oil always with a fatty meal
· In this study absorption ran rTG > natural TG > EE; it measured EPA/DHA in plasma, not health outcomes
· But choosing the right form isn't enough — next step, check freshness

3 · TOTOX oxidation ladder

and oxidize easily, first into hydroperoxides and then into fishy aldehydes and ketones, and TOTOX adds the two stages of oxidation into one number./ in fish oil are highly unsaturated fatty acids (5-6 double bonds), among the most oxidation-prone edible fats known. Oxidation has two stages:

Stage 1 · primary oxidation (PV, peroxide value)
· + O₂ → hydroperoxide (LOOH)
· Tasteless, colorless, unstable, intermediate for downstream reactions

Stage 2 · secondary oxidation (AV, anisidine value)
· LOOH → aldehydes + ketones + short-chain acids (hexanal / 2,4-decadienal / acrolein)
· These are the chemical root of "fishy nausea" — the fishy taste of your burps is the signal that the EPA/DHA has already oxidized

TOTOX formula (Total Oxidation value, GOED standard):

TOTOX = 2 × PV + AV

· TOTOX < 26: internationally accepted upper limit (GOED + EU)
· TOTOX < 10: excellent freshness
· Albert 2015 tested 32 fish oil products on the New Zealand market: 50% exceeded the recommended TOTOX limit, and 83% exceeded the recommended peroxide value (PV)

Oxidized fish oil is not just ineffective — hydroperoxides + aldehydes are pro-oxidant in reverse, and some studies observe mild elevation of liver enzymes. `Fish oil with oxidation value > 26 is worse than not taking it at all.`

4 · Decision tree

Decide from your fatty-fish intake whether you need a supplement, then pick rTG over over EE, look for TOTOX below 10, take it with meals and refrigerate it."Should I buy fish oil / what should I buy / how should I use it" decision tree:

Step 0 · Do you need fish oil supplements?

· ≥ 2 servings of fatty fish per week (salmon/sardine/mackerel/trout) → no supplement needed
· High (> 500 mg/dL) / secondary prevention → prescription high-purity ethyl ester (Vascepa) 4 g/day; note that in REDUCE-IT more people on the drug were hospitalised for atrial fibrillation or flutter (3.1% vs 2.1%), and serious bleeding was slightly more common (2.7% vs 2.1%, not statistically significant), so people with atrial fibrillation or on blood thinners should raise this with their doctor first
· Pregnancy / lactation + no fish intake → algal-oil ≥ 200 mg/day

Step 1 · choose form: rTG > TG > EE

Step 2 · verify freshness

· Look for TOTOX < 10 label (or PV < 5 meq/kg + AV < 20)
· IFOS / GOED third-party certification (factory testing)
· Brands without these numbers: switch immediately

Step 3 · usage

· Take with meals (a fatty meal promotes EE absorption)
· Refrigerate (after opening)
· Use within 2-3 months (oxidation accelerates after opening)
· Fishy burps / nausea = already oxidized, throw out immediately

1000 mg fish oil ≠ 1000 mg ω-3. A standard capsule contains only ~ 300 mg EPA+DHA, so the AHA 1 g/day target requires 3-4 capsules. Cheap fish oil + high dose = highly likely to be eating fats with oxidation values over the limit.

Full mechanism, in text

1 · Three forms

2 · Lipase + bile · absorption gap

3 · TOTOX oxidation ladder

4 · Decision tree

Fish oil · forms · TOTOX freshness

Full mechanism, in text

1 · Three forms

2 · Lipase + bile · absorption gap

3 · TOTOX oxidation ladder

4 · Decision tree

Fish oil · forms · TOTOX freshness