Fish oil is rich in Omega-3 polyunsaturated fatty acids (PUFAs), which have many positive effects on human health and reducing the risk of diseases. As a result, there is a growing demand for fish oil intake among people[1].
Omega-3 polyunsaturated fatty acids include alpha-linolenic acid (ALA; 18:3), stearidonic acid (SDA; 18:4), eicosapentaenoic acid (EPA; 20:5 ω-3), docosapentaenoic acid (DPA; 22:5 ω-3), and docosahexaenoic acid (DHA; 22:6 ω-3). Over the past few decades, scientists have conducted numerous studies on Omega-3 polyunsaturated fatty acids, primarily focusing on EPA and DHA, and have found that they have positive effects on cardiovascular diseases, diabetes, cancer, Alzheimer’s disease, dementia, depression, vision, and neural development[2].
The Benefits of Fish Oil, but How Much Should You Take?
The Food and Agriculture Organization (FAO) of the United Nations recommended in 2010[3]:
- For adult males and non-pregnant/non-lactating adult females, it is recommended to consume at least 250 milligrams of EPA and DHA per day. However, there is no research data indicating the minimum intake when supplementing EPA or DHA separately.
- For adult pregnant and lactating females, to ensure the health of both the mother and the fetus, a minimum daily intake of 300 milligrams of EPA and DHA is recommended, with at least 200 milligrams being DHA.
In 2020, Taiwan’s Food and Drug Administration of the Ministry of Health and Welfare restricted the daily intake limit of EPA and DHA to not exceed 2 grams, based on the total daily intake amount (EPA and DHA combined). For “specific disease formula foods” registered and issued permits by the Ministry of Health and Welfare, this limit was adjusted to a total daily intake (EPA and DHA combined) not exceeding 5 grams[4].
The Institute of Medicine of the United States recommended Dietary Reference Intake (DRI) for different age groups in 2005, as shown in the table below[5]:
| Age Group | Male | Female |
| 1-3 years | 700 mg | 700 mg |
| 4-8 years | 900 mg | 900 mg |
| 9-13 years | 1200 mg | 1000 mg |
| 14 years and older | 1600 mg | 1100 mg |
People can adjust their fish oil intake based on their specific health needs.
What Are the Different Forms of Fish Oil?
Currently, marine-based fish oil is the most common source of Omega-3 polyunsaturated fatty acids, typically containing between 20% and 30%. DHA and EPA make up over 80% of these Omega-3 polyunsaturated fatty acids[6]. The bioavailability of Omega-3 polyunsaturated fatty acids is greatly influenced by their form. Besides existing as free fatty acids (FFAs), they can also be classified into ethyl esters (EEs), triacylglycerides (TAGs), or phospholipids (PLs)[7].
In unrefined fish oil (natural fish oil), most of the Omega-3 polyunsaturated fatty acids are in the form of triglycerides (TGs) and as free fatty acids (FFAs). Unrefined fish oil contains varying amounts of EPA and DHA, and the concentration of Omega-3 polyunsaturated fatty acids in unrefined fish oil is lower[8].
Commercial fish oil products available in the market are processed and purified to convert EPA and DHA into different forms, such as ethyl esters (EEs) or re-esterified triglycerides (rTGs)[8]. The initial purification process typically results in ethyl ester (EE) form, where ethyl esters replace and remove the original glycerol backbone. Subsequently, some advanced purification processes convert EE fish oil back into triglyceride (TG) form, known as re-esterified triglycerides (rTGs), during which esterification enzymes remove ethyl esters and reintroduce the glycerol backbone[9].
Which Form of Fish Oil Has Better Absorption?
In recent years, many studies have indicated that the re-esterified triglyceride (rTG) form of Omega-3 polyunsaturated fatty acids has better absorption speed and efficiency compared to other forms, with significantly better bioavailability[10]. This is because in the human gastrointestinal tract, EE-form fish oil requires esterification enzymes to hydrolyze the ester bond and release absorbable free fatty acids in the small intestine, whereas TG-form fish oil does not require this step to release free fatty acids, making it more suitable for those with digestive issues[11].
A double-blind study involving 150 subjects randomly assigned to three groups: (1) concentrated fish oil containing EPA+DHA (1.01g+0.67g) in re-esterified triglyceride form (rTG group); (2) placebo group (given corn oil); (3) concentrated fish oil containing EPA+DHA (1.01g+0.67g) in ethyl ester form (EE group). After six months, the Omega-3 index on the red blood cell membrane of the subjects was measured as a comparison. The results showed a significant increase in the Omega-3 index for both experimental groups. Additionally, the rTG group’s index increase was significantly higher than the EE group, indicating better absorption when consuming fish oil in rTG form[12]. Another study comparing the absorption differences among the EE group, free fatty acid group, and rTG group, with 72 participants assigned to orally ingest different forms of EPA+DHA (approximately 3.3 grams) continuously for two weeks. Blood samples measured the Omega-3 polyunsaturated fatty acids in the forms of EE, TGs, and PL in the subjects’ fasting serum, revealing that the rTG group had the highest bioavailability, while the EE group had the lowest, suggesting that the bioavailability of the rTG group is significantly greater than the EE group[13].
Hence, choosing to consume Omega-3 polyunsaturated fatty acids in rTG form ensures the best bioavailability of fish oil in the human body. However, due to the additional processing steps required for rTG fish oil manufacturing, the price is generally higher than EE fish oil.
Is the Type of Fish Oil Related to Concentration?
Based on various studies, it is known that the type of Omega-3 polyunsaturated fatty acids can affect bioavailability, influencing absorption after intake. But is the type of fish oil related to concentration? A study was conducted using four different types of fish oil, with participants taking supplements for four weeks, divided into the following groups:
- Reesterified triglyceride (rTG) form of fish oil: 650 mg EPA, 450 mg DHA;
- Ethyl ester (EE) form of fish oil: 756 mg EPA, 228 mg DHA;
- Phospholipid (PL) form of krill oil: 150 mg EPA, 90 mg DHA;
- Triglyceride (TG) form of salmon oil: 180 mg EPA, 220 mg DHA.
The results indicated that the increase in whole blood Omega-3 fatty acid concentration among participants was as follows: rTG group > EE group > TG group > PL group. Additionally, it was found that the daily intake of EPA and DHA in the rTG group was similar to the EE group. However, the EPA concentration in the blood of the rTG group was comparable to the EE group, and the DHA content in the rTG group was approximately four times higher. This suggests that the type of fish oil can affect absorption efficiency even with equivalent intake levels.
Based on these research findings, it is crucial to choose fish oil with a type that has high bioavailability, such as the rTG form. Concentration of fish oil is not an absolute influencing factor, as fish oil products on the market vary in concentration. Therefore, the type of fish oil is the most important consideration for consumers.
How Can I Distinguish the Type of Fish Oil?
Currently, there are no well-established methods by third-party organizations to verify the type of fish oil. However, there is one way to help consumers distinguish the type of fish oil they have. Commercially available fish oil products are typically highly refined and concentrated, with many of them being in the form of ethyl esters (EE) [9]. The structure of polystyrene, also known as “Styrofoam,” resembles a polyester structure [15]. The polarities of these two structures are similar. Therefore, if you drop ethyl ester (EE) type fish oil onto Styrofoam, it will cause the Styrofoam to dissolve. The Ministry of Health and Welfare also explains that this dissolving phenomenon is normal and due to the ethyl ester (EE) type of fish oil [16]. However, triglyceride (TG) or reesterified triglyceride (rTG) forms of fish oil will not dissolve Styrofoam because their structures have dissimilar polarities.
Therefore, sometimes people may use the dissolving of Styrofoam to assess the quality of fish oil, but this can only be used as an indicator of the fish oil type. Hence, when choosing fish oil, consumers should pay close attention to the type of fish oil, with the rTG type (non-dissolving Styrofoam type) being the most important factor to consider.
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