What are EPA and DHA

Omega-3 fatty acids: linseed oil instead of fish oil?

Dr. Katrin Kuhnt

Overfished seas, high concentrations of heavy metals in fish and species that are on the verge of extinction: the supply of fish and marine animals and thus also of the valuable omega-3 fatty acids is becoming scarce. Alternative sources are in demand and so the University of Jena is investigating what contribution vegetable oils can make.

© Working Group Omega-3 e.V.

Sea fish contains a particularly large amount of long-chain omega-3 fatty acids - also known as n-3 fatty acids. These unsaturated fatty acids have anti-inflammatory effects, improve the flow properties of the blood and can prevent heart diseases. The German Nutrition Society (DGE) therefore recommends eating fish twice a week. As an alternative to marine animals, research has focused on vegetable oils with a high proportion of omega-3 fatty acids. Current studies at the University of Jena are investigating whether these vegetable oils also have a positive effect on various human blood fractions. The investigations belong to the project "Metabolism and cardioprotective effectiveness of vegetable‘ land-based ‘n-3-fatty acids", which was funded by the German Research Foundation.

Complicated metabolism of fatty acids

Alpha-linolenic acid (ALA), one of the vegetable omega-3 fatty acids, is essential for humans. The DGE experts recommend taking in 0.5% of the total energy from alpha-linolenic acid, which corresponds to around 1.5 grams per day. While the most commonly used rapeseed and soybean oils contain around 7-10% ALA, linseed oil is the best food source with up to 60%. One tablespoon of linseed oil provides around 2-4 grams of ALA. Walnut, rapeseed or hemp oil are also valuable sources, as are linseed and walnuts. Perilla oil also contains a very high proportion of ALA at around 60%; however, its use is mainly restricted to Asian countries. Echium oil, approved as a novel food in Europe since 2008, has an ALA content of 30-40% and also contains significant amounts of stearidonic acid (SDA, C18: 4 n-3), which has one more double bond than ALA (C18: 3 n-3) has. Echium oil is obtained from the seeds of plants belonging to the Boraginaceae family; Species of the so-called adder's head - Echium vulgare and Echium plantagineum - are used for the oil.

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Linoleic acid, an omega-6 fatty acid, is also essential. It is found mainly in safflower, sunflower, corn germ and soybean oil. Both alpha-linolenic acid (ALA) and linoleic acid (LA) are lengthened or converted in the metabolism with the help of the same enzymes and are therefore in competition with one another. The extension of ALA to its long-chain and biologically effective metabolites eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) is therefore limited. Researchers estimate that adults convert around 5-10 percent of alpha-linolenic acid into EPA and 0.5 percent into DHA.

Vegetable sources as starting material

Despite the limited conversion rates, ALA plays an essential role in this country as a raw material for EPA and DHA. Using intervention studies, the scientists from Jena have now investigated whether ALA supplementation leads to an effective accumulation of these long-chain omega-3 fatty acids in the three blood fractions plasma, red blood cells and immune cells such as monocytes or lymphocytes. Does this improve the omega-3 status and the ratio of fatty acids in the body? And does the consumption of vegetable oils lead to an accumulation of EPA and DHA in the blood? ALA-rich oils such as linseed oil and echium oil were used for the project. During the test phase, the participants were not allowed to eat fish, linseed or rapeseed oil.

A total of 154 test subjects took part in the randomized, double-blind controlled intervention studies. The study participants were divided into groups according to age, gender and metabolic situation and received different omega-3-rich vegetable oils or control oils (fish oil, olive oil) for eight weeks.

Better blood values ​​through vegetable oils

One sub-study, for example, exclusively examined the group of 21 young subjects with healthy metabolism (on average 26 years old) who received two tablespoons of echium oil daily for a period of eight weeks. During the course of the study, the blood lipid levels improved and the levels of EPA in the blood increased. In a further study, the subjects were on average 62 years old, overweight and suffered from high blood pressure and disorders of blood sugar metabolism, i.e. from a premetabolic syndrome. Participants - nine men and ten women - were given two tablespoons of ALA-rich oil a day for eight weeks. When comparing the values ​​from the beginning of the study and after eight weeks, around twice as many omega-3 fatty acids were found in the blood. In addition, the blood pressure and blood fat values ​​improved.

Overall, all subjects in the various study groups had higher levels of ALA and long-chain omega-3 fatty acids in plasma, erythrocytes and white blood cells as a result of the supplementation. On average, the omega-3 fatty acids increased 1.5 to 2-fold in all blood fractions over the eight-week intervention period with linseed oil. The highest increase occurred within the first week of intervention. The ratio of omega-6 to omega-3 fatty acids also improved over the entire duration of the study. The intake of linseed oil also had an influence on the blood lipids: while the triglycerides remained unchanged, the total cholesterol and the "bad" LDL cholesterol in the serum of the male test subjects fell. At the same time, the “good” HDL cholesterol increased significantly in both sexes and the LDL / HDL ratio decreased. Blood pressure also tended to improve.

Problem case, decreasing DHA levels

In the course of the studies with the ALA-rich vegetable oils, however, the proportion of DHA in the blood decreased. One explanation is the limited conversion of ALA to its long chain metabolites. Results from Australian scientists suggest that DHA enrichment through the sole intake of ALA as a source of long-chain omega-3 fatty acids is possible when the levels of other polyunsaturated fatty acids, especially linoleic acid (omega-6) in the diet, are low are. The usual diet, however, contains a high intake of saturated fatty acids and omega-6 fatty acids with a low proportion of omega-3 fatty acids. The ratio of omega-6 to omega-3 fatty acids is therefore now around 8 to 15: 1, a value of 5: 1 is considered desirable. This also limits the conversion rate and could presumably also be improved with a different food composition.

The intervention-related reduction in the DHA content in the blood fractions does not, however, have to mean that less DHA is also found in the tissues. In older animal experiments, DHA accumulation in the brain was observed as a result of the supplementation of ALA, while the values ​​in the plasma and in the heart and liver tissue did not change. Another explanation for the decreasing DHA levels in the blood could be that foods rich in EPA and DHA, such as fish, should be avoided for the entire duration of the intervention. Thus, the decreasing DHA content can also be related to the reduced intake through food.

Body adapts to intake

In humans, the rate of conversion of alpha-linolenic acid to EPA and DHA depends not only on the composition of the diet but also on the individual nutritional status. If food intake is scarce, the body probably builds more EPA and DHA from ALA. This is suggested by data from the EPIC study (European Prospective Investigation into Cancer and Nutrition). Researchers determined what the metabolic status of alpha-linolenic acid, EPA and DHA looks like in different diets. They divided into fish eaters, non-fish eaters, vegetarians and vegans. The results showed that the largest proportion of EPA and DHA came from fish and that the total intake of omega-3 fatty acids in the non-fish eaters was only between 57 and 80 percent of the fish eaters. However, the blood status was less different than the researchers expected. As a result, the conversion rate of alpha-linolenic acid to EPA and DHA may increase if the food contains only small amounts of EPA and DHA over the long term.

More omega-3 from vegetable oil is worth it

According to these studies, linseed oil and other vegetable oils that are rich in alpha-linolenic acid contribute to the metabolism of various long-chain omega-3 fatty acids such as eicosatetraenoic and eicosapentaenoic acid as well as docosapentaenoic acid. are formed. These fatty acids accumulate in the blood fractions plasma, erythrocytes and other blood cells through an ALA intervention and thus improve the status of the omega-3 fatty acids in tissue. Linseed oil and other ALA-rich vegetable oils are, however, only partially suitable for completely replacing fish as sources of long-chain omega-3 fatty acids in the human diet, since the DHA drop could not be compensated for by the ALA supplementation. However, ALA-rich vegetable oils have the potential to counteract a low intake of omega-3 fatty acids and prevent an omega-6 excess in the Western diet. The prerequisite is to use linseed oil and other ALA-rich oils in the long term instead of conventionally used oils such as sunflower or corn oil, which are rich in omega-6 fatty acids. The conversion to DHA may then increase further.

Source: Kuhnt K: UGBForum 6/14, pp. 297-300