How microalgae, fish, and krill store omega-3s differently and why it matters

By Vijay Kumar MalesuReviewed by Susha Cheriyedath, M.Sc.Jan 28 2026

A detailed lipidomic comparison reveals that EPA and DHA are packaged very differently across marine sources, challenging the idea that all omega-3s are nutritionally equivalent.

Study: Omega-3 Source Matters: Comparative Lipid Signatures and Quantitative Distribution of EPA/DHA Across Marine Resources. Image Credit: I. Noyan Yilmaz / Shutterstock

In a recent study published in the journal Marine Drugs, a group of researchers compared how different marine sources store eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) across lipid classes and evaluated their comparative nutritional characteristics.

Background: Why Omega-3 Structure Matters

Heart disease remains the leading global cause of death, yet something as simple as choosing the right dietary fat can meaningfully reduce risk. Omega-3 fatty acids, mainly EPA and DHA, are very important for a healthy heart, brain, and metabolism.

Traditionally, seafood has been the primary dietary source of EPA and DHA. However, growing sustainability pressures and reported reductions in omega-3 levels in some fish species have accelerated interest in alternative sources, including microalgae and microbial oils. This shift raises questions about why these sources are increasingly favored.

It is important to note that the structural form of fat molecules may influence digestion, transport, and metabolic handling, rather than absorption alone. Further research is needed to determine which lipid forms and class distributions of omega-3 fatty acids matter most, not just total quantity.

Study Design and Marine Sources Analyzed

A lipid analysis was conducted on various marine omega-3 sources, including 12 microalgal species, 1 heterotrophic marine protist (Schizochytrium species), 4 oily fish species, and 9 commercial omega-3 supplements derived from fish, krill, and algae.

Lipids were extracted from dried biomass or oil samples using standardized solvent-based methods to preserve lipid integrity.

Lipid Separation and Fatty Acid Quantification

Researchers used high-performance thin-layer chromatography to separate complex lipids into classes such as phospholipids, glycolipids, and neutral lipids. Individual lipid bands were isolated and converted into fatty acid methyl esters.

Gas chromatography-mass spectrometry was then used to quantify EPA and DHA content in each lipid class.

Nutritional Indices and Lipid Quality Assessment

Nutritional indices were calculated from fatty acid profiles to assess relative lipid quality and cardiometabolic relevance.

The ratio of polyunsaturated to saturated fatty acids was evaluated, with higher values considered favorable. Additional indices included the index of atherogenicity, the index of thrombogenicity, the lipid quality index, and the ratio of hypocholesterolemic to hypercholesterolemic fatty acids. These measures serve as comparative indicators rather than direct health outcomes.

All analyses were conducted in triplicate, and results were expressed on a dry-weight basis to support reliable cross-source comparisons.

EPA and DHA Distribution in Microalgae

Substantial differences were observed in both the amounts and the structural distributions of EPA and DHA across marine sources.

Microalgae generally contained high levels of EPA but low levels of DHA, with some species showing more than 40% of total fatty acids as EPA. Notably, EPA in microalgae was predominantly embedded within glycolipids and phosphatidylglycerol, key components of photosynthetic membranes, rather than stored as energy lipids.

This structural positioning suggests a biological role beyond energy storage and may influence downstream metabolic handling, although this was not directly evaluated in the study.

Lipid Profile of Schizochytrium Species

The heterotrophic protist Schizochytrium species showed the opposite pattern, with high DHA content (approximately 33% of total fatty acids) and relatively low EPA levels.

More than 85% of its lipids were stored as triacylglycerols, indicating an energy-reserve profile that closely resembles refined algal oil supplements.

Omega-3 Profiles in Fish Species

Fish species typically contained more DHA than EPA, although both were present in nutritionally meaningful amounts.

Anchovies and sardines emerged as efficient dietary sources of omega-3 fatty acids, thanks to their favorable lipid profiles and small serving sizes. While temporal trends could not be assessed, measured EPA and DHA levels were lower than values reported in earlier literature, aligning with reports of declining omega-3 content linked to climate change and shifts in aquaculture feed composition.

Commercial Omega-3 Supplements

Commercial omega-3 supplements varied substantially in lipid structure.

Refined fish oil capsules contained high levels of EPA and DHA, stored almost entirely as triacylglycerols, with phospholipids largely removed during processing. Krill oil supplements differed structurally, with nearly one-third of total lipids present as phosphatidylcholine.

This phospholipid-bound form has been associated in prior research with altered digestion and tissue distribution, although the present study focused on compositional differences rather than physiological effects.

Algal oil capsules provided the highest DHA concentrations and required the smallest intake to meet dietary recommendations. Like fish oil, omega-3 fatty acids were primarily stored as neutral lipids.

Health-Related Lipid Indices Across Sources

Health-related lipid indices reinforced observed compositional patterns.

Algal oils and selected microalgae exhibited the most favorable polyunsaturated-to-saturated fatty acid ratios and hypocholesterolemic-to-hypercholesterolemic ratios. Krill oils showed more variable results, while fish and fish oils generally fell within moderate but acceptable index ranges.

Conclusions and Nutritional Implications

These findings demonstrate that omega-3 sources are not nutritionally equivalent.

Beyond total EPA and DHA content, the lipid structures carrying these fatty acids represent an additional layer of nutritional differentiation. Microalgae primarily deliver EPA within membrane-associated glycolipids, whereas fish and refined oils store omega-3 fatty acids mainly as energy-dense triacylglycerols.

Krill oil lipids contain a higher proportion of phospholipids, distinguishing them structurally from triacylglycerol-dominated oils, although overall lipid quality indices were more variable.

As sustainability concerns increase and dietary patterns evolve, evaluating omega-3 sources by lipid class, rather than only by quantity, may enable more nuanced nutritional comparisons and guide future research, rather than serving as direct dietary guidance.