Fish oil absorption
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Forms of Fish Oil and Their Absorption Efficiency
Fish oil fatty acids can be delivered in several forms, including triacylglycerols, free acids, and ethyl esters. The absorption of these forms varies significantly. Free acid forms of fish oil fatty acids are absorbed very efficiently, with absorption rates of at least 95%. In contrast, when fish oil is provided as triacylglycerols, the absorption of key omega-3 fatty acids like eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) drops to 68% and 57% of the free acid absorption, respectively. Ethyl ester forms are absorbed even less efficiently, at only about 20% of the rate seen with free acids. These differences are linked to how well pancreatic lipase can break down each form for absorption in the gut15.
Impact of Meal Fat Content on Fish Oil Absorption
The amount of fat consumed with fish oil supplements can greatly influence absorption. When fish oil triacylglycerols are taken with a high-fat meal, the absorption of EPA increases from 69% to 90%. For ethyl ester forms, absorption of both EPA and DHA increases threefold, reaching about 60% when taken with a high-fat meal. This shows that the presence of dietary fat is especially important for the absorption of ethyl ester forms of fish oil.
Fish Oil Delivery Systems: Emulsified, Encapsulated, and Bulk Liquid
The way fish oil is formulated also affects how well it is digested and absorbed. Emulsified fish oil, which is fish oil mixed with stabilizers to form a fine dispersion, shows the highest rate of free fatty acid release and absorption compared to encapsulated (gelatin capsule) and bulk liquid forms. In both laboratory and animal models, emulsified fish oil led to significantly higher absorption rates of DHA and other omega-3 fatty acids than encapsulated or bulk liquid forms24. Human studies confirm that emulsified fish oil results in greater increases in blood levels of omega-3 fatty acids compared to standard capsule forms, and is also well tolerated by users.
Special Considerations: Hydrogenated Fish Oil and Aging
Totally hydrogenated fish oil, which contains very-long-chain saturated fatty acids, is absorbed much less efficiently than other forms of fish oil. In animal studies, only about 61% of the fat from totally hydrogenated fish oil was absorbed, compared to 95-99% for other oils. This low absorption is mainly due to the poor uptake of very-long-chain saturated fatty acids.
In aging models, diets enriched with fish oil can help maintain lipid absorption by slowing the degeneration of intestinal villi, which are important for nutrient uptake. This suggests that fish oil may help counteract age-related declines in fat absorption.
Comparison of Fish Oil with Other Marine Oils
Phospholipid-enhanced fish oil and krill oil have similar overall absorption of EPA and DHA, but the absorption profile differs. Phospholipid-enhanced fish oil leads to a higher and earlier peak in blood levels of these fatty acids compared to krill oil, which may be relevant for certain health outcomes.
Fish Oil vs. Other Dietary Fats
Compared to corn oil, fish oil and fish oil concentrates are absorbed less efficiently in animal models. However, fish oil feeding increases the ratio of EPA to arachidonic acid in the lymph, which may have health benefits despite the lower overall absorption.
Conclusion
Fish oil absorption depends on the chemical form (free acid, triacylglycerol, ethyl ester), the delivery system (emulsified, encapsulated, bulk), the fat content of the accompanying meal, and the specific type of oil (including hydrogenated forms). Emulsified and free acid forms are generally absorbed best, especially when taken with a high-fat meal. These findings are important for consumers and manufacturers aiming to maximize the health benefits of fish oil supplements.
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