Fish oilWhich form of fish oil is absorbed best?
Short answer
What the forms are
Fish oil supplements come in several chemical forms:[2]
- natural triglycerides: the form found in fish oil itself[2]
- ethyl esters: made from natural triglycerides by replacing glycerol with ethanol[2]
- re-esterified triglycerides: ethyl esters turned back into triglycerides[2]
- free fatty acids: fatty acids not bound to glycerol[2]
- phospholipids: the main form in krill oil[2]
Concentrated forms were developed to make fish oil easier to keep taking.[1]
What studies found
In a 2010 study, 72 volunteers took about 3.3 g of EPA and DHA a day for 2 weeks.[1] Their blood levels, compared with natural fish oil, were:[1]
- re-esterified triglycerides: 124%, significantly better[1]
- free fatty acids: 91%, no significant difference[1]
- ethyl esters: 73%, significantly worse[1]
Another study differs on this. A 2021 crossover trial in 22 adults gave one dose of about 1.2 g with low-fat meals. Natural triglycerides and ethyl esters did not differ, and a third form, monoglycerides, gave higher blood EPA. Side effects were similar for all three.[3]
The fat in the meal also matters, especially for ethyl esters. In a 1988 study in men, a meal with 44 g of fat raised absorption of ethyl esters three-fold compared with 8 g. Natural fish oil gained less, with EPA absorption rising from 69% to 90%.[4]
Krill oil and algal oil
Krill oil contains omega-3 fats mainly as phospholipids. Some studies suggest somewhat better absorption than fish oil, and others do not.[2] A 2020 network review of 64 trials found no difference between krill oil and fish oil in their effects on blood fats.[5] One gram of omega-3 lowered triglycerides by about 9 mg/dL from fish oil and about 10 mg/dL from krill oil.[5]
Algal oil is the vegetarian option. It usually gives 100 to 300 mg of DHA, and some products also contain EPA.[2] One small study found that DHA from algal oil was absorbed as well as DHA from cooked salmon.[2]
Does better absorption mean a better result?
This is not known. The krill and fish oil review found that the fall in triglycerides depended on the dose of omega-3, whatever the source.[5] Different forms were tested in separate trials, and those trials also differed in dose and people.[2]
Who should be careful
Trials found more atrial fibrillation at 4 g a day with both an ethyl ester and a carboxylic acid form.[6][2] Formulas vary widely, so the amount of EPA and DHA on the label matters when you compare products.[2] People who take a blood thinner or have a heart condition should ask a doctor or pharmacist first.[2]
Sources (6)
- Bioavailability of marine n-3 fatty acid formulations. Dyerberg J, Madsen P, Møller JM, Aardestrup I, Schmidt EB Prostaglandins Leukot Essent Fatty Acids, 2010. PMID 20638827
- Omega-3 Fatty Acids: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. ods.od.nih.gov
- Pharmacokinetics of Supplemental Omega-3 Fatty Acids Esterified in Monoglycerides, Ethyl Esters, or Triglycerides in Adults in a Randomized Crossover Trial. Chevalier L, Vachon A, Plourde M J Nutr, 2021. PMID 33564872
- Absorption of eicosapentaenoic acid and docosahexaenoic acid from fish oil triacylglycerols or fish oil ethyl esters co-ingested with a high-fat meal. Lawson LD, Hughes BG Biochem Biophys Res Commun, 1988. PMID 2847723
- Lipid-modifying effects of krill oil vs fish oil: a network meta-analysis. Kim MG, Yang I, Lee HS, Lee JY, Kim K Nutr Rev, 2020. PMID 32073633
- Cardiovascular Risk Reduction with Icosapent Ethyl for Hypertriglyceridemia. Bhatt DL, Steg PG, Miller M, Brinton EA, Jacobson TA, Ketchum SB, et al. N Engl J Med, 2019. PMID 30415628
More about fish oil
What is fish oil?Does fish oil reduce inflammation?How much EPA and DHA is in a fish oil capsule?Is eating fish better than taking fish oil?What is fish oil used for?Should fish oil be taken with food?For education; not medical advice. Talk to a doctor before you start, stop or change a supplement.