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Polyunsaturated fatty acids (PUFA, Omega-3 & -6)
Did you know that polyunsaturated fatty acids (PUFAs) are important for the brain, cells, and skin? However, pay attention to the ratio of omega-6 to omega-3, as an imbalance can cause health problems. Read more in our article.
A balanced, plant-based diet with few to no industrially processed foods generally provides sufficient macro- and micronutrients, with the exception of vitamin B12. However,phytochemicalsare particularly relevant for maintaining health and healing, even though they are not considered essential nutrients – apart from vitamins.
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Definition
Fatty acids with two or more carbon-carbon double bonds are called "polyunsaturated" – also known as PUFAs (polyunsaturated fatty acids).1
Due to the structural "kink" caused by the double bonds, PUFAs cannot be stacked as tightly as saturated fatty acids (SFAs). This also applies to monounsaturated fatty acids (MUFAs). This results in a lower melting point because of the weaker van der Waals forces (weak attractive interactions between loosely bonded atoms and/or molecules). Therefore, PUFAs with the same chain length as SFAs are in the liquid state at lower temperatures.
PUFAs: Omega-3 and Omega-6
PUFAs can be divided into two groups: Omega-3 (ω-3 or n-3) and Omega-6 fatty acids (ω-6 or n-6). This classification is based on the position of the first double bond at the methyl end (CH3, i.e., one carbon and three hydrogen atoms). An example is α-linolenic acid (ALA, C18:3, cis-9,12,15), in which the first double bond is located at the third position (ω-3 or n-3) from the methyl end – that is, between C-15 and C-16 (the 15th and 16th carbon atoms). The Omega-6 PUFA linoleic acid (LA, C18:2, cis-9,12) has its first double bond between C-12 and C-13, i.e., at the sixth position (ω-6 or n-6) from the methyl end, out of a total of 18 carbon atoms.
The two PUFAs mentioned above are essential, unlike the fatty acid groups (SFA and MUFA) described in other articles because the human body cannot produce them itself. 1,4As mentioned below, they serve as basic building blocks for other PUFAs that the body needs for various functions.
Occurrence
Important representatives of n-3-PUFAs and their typical food sources are:
Stearidonic acid (18:4, n-3, SDA) – fish such as sardines, salmon, herring and fish oils, hemp oil, blackcurrant seed oil.2
Eicosapentaenoic acid (20:5, n-3, EPA) – fish oil (especially oily fish such as salmon, herring, anchovies, smelt, and mackerel).2
Docosapentaenoic acid (22:5, n-3, DPA) – fish oil (especially oily fish such as salmon, herring, anchovies, smelt, and mackerel).2
Docosahexaenoic acid (22:6, n-3, DHA) – fish oil (especially oily fish such as salmon, herring, anchovies, smelt, and mackerel).2
Note: The listed oils represent the most concentrated form of the respective foods that contain these PUFAs in their natural form. Therefore, they are not a natural or near-natural source. The consumption of fish for EPA and DHA is controversial due to heavy metal contamination and overfishing of the oceans.4
Algae are the original source of EPA and DHA and offer a valuable alternative for people who want to avoid fish or animal products. They provide EPA/DHA directly and without the risks and environmental concerns of fish consumption. For vegans, purified algae oil is a particularly suitable option, if supplementation is necessary or advisable at all.30
Important representatives of n-6-PUFAs and their typical food sources are:
Dihomo-gamma-linolenic acid (20:3, n-6, DGLA) – found in small amounts in animal tissues.2
Arachidonic acid (20:4, n-6, AA or ARA) – animal fats, liver, egg lipids (fats from eggs), and fish.2
Docosatetraenoic acid or adrenic acid (22:4, n-6, ADA) – found in small amounts in animal tissues.2
Docosapentaenoic acid (22:5, n-6, DPAn-6) – found in small amounts in animal tissues. Important: Here it is also called "docosapentaenoic acid" (as in DPA). Two omega fatty acids with this name are mentioned in the literature. These are isomers, meaning chemical compounds with the same number of atoms of the respective elements, but with different chemical structures. One is the omega-3 fatty acid DPA, the other is the omega-6 fatty acid DPAn-6, also known as osbondic acid.
Note: Here too, one of the cited studies primarily lists oils that contain large amounts of omega-6 fatty acids. However, over the last three decades, people, especially in the West and North America, have been consuming increasingly higher proportions of omega-6 fatty acids, accompanied by a decrease in omega-3 fatty acids; this has led to a sharp increase in the omega-6 to omega-3 ratio (from 1:1 during evolution to 20:1 or even higher today).5 Therefore, one should be cautious with foods containing high amounts of omega-6 fatty acids and avoid them if possible. See the recipe for Erb-Muesli. It is designed to compensate for a day with too many omega-6 fatty acids relative to omega-3 fatty acids.
Omega-3 & Omega-6: Competition and Consequence
Here, we will discuss in more detail why a poor ratio of omega-6 to omega-3 fatty acids can have negative effects on our health. The main reason lies in the competition for enzymes that are necessary for the further metabolism (conversion and utilization) of the essential PUFAs. This is because PUFAs are the target of the same group of enzymes that compete to metabolize omega-6 and omega-3 fatty acids.7
Products made from ALA and LA exert antagonistic (opposing) functions in the human body. Most omega-6 PUFA products primarily promote inflammation, platelet aggregation (clumping of blood platelets), and vasoconstriction (narrowing of blood vessels), while omega-3 products inhibit inflammation and platelet aggregation and promote vasodilation (widening of blood vessels).7
As a consequence of increased omega-6 fatty acid consumption combined with a poor omega-6 to omega-3 fatty acid ratio, there is a demonstrable excess of products derived from linoleic acid and arachidonic acid. Scientists consider this the main cause of thrombus formation (blood clots that can lead to blockages of small blood vessels), allergic and inflammatory diseases, and an overactive endocannabinoid system (which influences energy balance, eating habits, lipoprotein metabolism, insulin sensitivity, and glucose/blood sugar levels).6,7
It is not surprising that researchers also see a link (between fatty acid imbalance and obesity), as the next referenced article reveals.6 In this review, the authors state that experimental studies show that omega-6 and omega-3 fatty acids have different effects on the increase of body fat via various mechanisms. These include, among others, adipogenesis (fat storage), browning of adipose tissue (introduction of thermogenically active adipocytes into white fat depots—these promote the conversion of excess fat depots into heat production = "fat burning"), lipid homeostasis, the brain-gut-fat axis, and, most importantly, systemic inflammatory responses.6
The authors also explain that recent human studies show that, in addition to the absolute amounts of omega-6 and omega-3 fatty acids, the ratio of these fatty acids also plays an important role in the development of obesity. This can be reversed by increasing the intake of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Therefore, a balanced omega-6/omega-3 ratio is considered important for health and for the prevention and treatment of obesity.6 A systematic review from 2017, which evaluated 35 studies on PUFAs in 17 European countries, showed, specifically with regard to EPA and DHA, that only about 26 % of countries meet the average intake recommendations.8
One study demonstrated that even a reduction in linoleic acid (LA) intake increases omega-3 PUFA status in humans without an increase in omega-3 PUFA intake (this involved a reduction from ~5 % to <2,5 % of energy (% E) over 4 weeks in 36 participants).9 This is likely due to the aforementioned competition for processing enzymes, which, in the presence of a significant excess of omega-6 fatty acids, reduce the proportion available for omega-3 PUFA metabolism and consequently decrease the bioavailability of the resulting products. Undesirable chronic health conditions, which can be exacerbated by an excessive effect of omega-6 hormones, can be avoided by a diet higher in omega-3 fats, lower in omega-6 fats, and lower in calories per meal.10
Storage and Preparation Losses
Polyunsaturated fatty acids such as ALA and LA are sensitive to oxidation by molecular oxygen (O₂) from the air. Oils with a high LA or ALA content should be stored protected from light and oxygen, at cool temperatures, and consumed as soon as possible. To optimally utilize the nutrients in oilseeds, one should use seeds that have already been processed or ground into grits. However, after grinding, the seeds are very sensitive to oxidation, which is why it is advisable not to store them further but to consume them immediately.
Nutrition – Health
Omega-6 fatty acids like LA and omega-3 fatty acids like ALA are essential for us. Due to poor dietary habits and their widespread presence in common dietary fats, many people consume too much LA, resulting in omega-3 fatty acid intake that is often lower than ideal. This exacerbates the potential consequences discussed above.
Humans and animals cannot produce omega fatty acids themselves and must therefore obtain them through their diet. Only plants can produce them.5,11
PUFAs are essential for humans, as they play a central role in the optimal development of the brain, blood cells, and skin.2,5 Highly specialized membranes such as synaptic terminals, retinal cells, and cardiac muscle cells also contain very high amounts of arachidonic acid (AA) and docosahexaenoic acid (DHA) for structural lipids (e.g., very fluid membranes due to the many kinks caused by the double bonds) and functional roles (e.g., receptor functions, ion channels, neurotransmitter release).2
Even though we in Western countries often suffer from an excess of lactic acid (LA), it's important to be aware that LA also provides essential functions for the body (when consumed in a good balance). From a physiological perspective, arachidonic acid and dihomo-gamma-linolenic acid (DGLA) are the most important conversion products of LA. However, an excess of LA combined with a deficiency of ALA is not beneficial to our health. For this and the reasons mentioned above, it's important to pay attention to a balanced PUFA ratio. Nutritionists recommend an LA:ALA ratio of less than 5:15,7, and we also suggest this in the editorial linked here.
The EFSA recommends the following intake levels for optimal omega-3 and omega-6 fatty acid intake:25
2 g for short-chain omega-3 fatty acids such as α-linolenic acid.
200 mg for long-chain omega-3 fatty acids such as EPA and DHA.
6g for omega-6 fatty acids such as linoleic acid.
Deficiency symptoms
A deficiency in essential fatty acids (omega-3 or omega-6 fatty acids) can lead to dry, flaky skin and dermatitis (skin inflammation).27
The Western diet is deficient in omega-3 fatty acids and excessive in omega-6 fatty acids. While the optimal ratio is approximately 1:1, the Western diet typically has a ratio exceeding 10:1. This deficiency in omega-3 fatty acids and the excess of omega-6 fatty acids promote the development of cardiovascular diseases, cancer, and inflammatory and autoimmune disorders. Conversely, a diet rich in omega-3 fatty acids may have a mitigating effect on these diseases.
Studies show that a 4:1 ratio in the secondary prevention of cardiovascular disease can reduce overall mortality by 70 %. In patients with colorectal cancer (cancer of the colon and rectum), a 2,5:1 ratio reduced cell proliferation (cell growth and multiplication), while a 4:1 ratio showed no effect.26
Functions in the body
There are numerous studies that postulate the positive effects of PUFAs, primarily omega-3 fatty acids:
PUFA and inflammation
Eicosanoids from PUFAs regulate local signaling between cells. Arachidonic acid produces pro-inflammatory eicosanoids, while EPA and DHA produce anti-inflammatory eicosanoids. Higher omega-3 PUFA consumption may therefore protect against inflammation, cancer, cardiovascular disease, and other chronic illnesses. Researchers at Toho University Sakura confirm that omega-3 PUFAs, especially EPA, have anti-inflammatory effects, while omega-6 PUFAs such as arachidonic acid can worsen inflammation. Omega-3 PUFAs can replace arachidonic acid in cell membranes. Recent reports indicate that DHA-rich fish oil is more effective at reducing inflammation than EPA-rich fish oil.12,13
PUFA and blood pressure
A 2002 meta-analysis shows that high doses of fish oil (3.7 g/day) slightly lower blood pressure, presumably by reducing vascular resistance, without affecting cardiac output.14 A 2017 review explains that omega-3 PUFAs improve endothelial function (endothelium = thin layer of cells lining the inside of blood vessels), dilate vessels, have antioxidant, anti-inflammatory, and antithrombotic effects, delay plaque formation, and reduce wall stiffness. Omega-3 PUFAs can influence blood pressure, but this effect is related to the omega-3 PUFA content in the membrane before treatment. However, the evidence for cardiovascular prevention through these fatty acids is still weak and requires further studies.15
PUFA and cardiovascular events
Many studies show differing results regarding the cardiovascular effects of omega-3 fatty acids. A study published in 2018 suggests that these discrepancies may be due to a lack of focus on patients with hypertriglyceridemia and low doses of omega-3 fatty acids. Therefore, in the REDUCE-IT study, researchers tested a high dose of 4 g/day of highly purified EPA in 8179 patients with hypertriglyceridemia and high cardiovascular risk over 4,9 years. They found that this dose reduced cardiovascular events by 25 %.13 It remains to be seen whether these results can be confirmed in further studies.
PUFAs and obesity as well as metabolic syndrome(MetS)
A 2019 meta-analysis shows that higher intake of omega-3 PUFAs reduces the risk of metabolic syndrome, while omega-6 PUFAs have no effect.16 The ratio of omega-6 to omega-3 PUFAs influences obesity, with increased eicosapentaenoic acid and docosahexaenoic acid potentially offsetting excess omega-6.6 A study of 311 children aged 7–12 years confirms that higher PUFA intake and a better PUFA-to-saturated-fat ratio are associated with more lean body mass and less visceral fat.17
PUFA and dry eye
Dry eye disease (keratoconjunctivitis sicca) is a multifactorial inflammatory condition. A study evaluated the effect of PUFAs on patients with this disease from 13 randomized clinical trials with a total of 1782 patients. It concluded that PUFAs are effective in treating nonspecific dry eye disease, particularly as a short-term treatment, with relatively few adverse events. Therefore, in clinical practice, it is reasonable to recommend PUFA supplementation to patients with this condition who are not concurrently taking other topical (locally acting) or systemic (body-acting) ophthalmic medications.18
PUFA and anxiety
Studies show that omega-3 PUFAs have a significant anxiolytic effect, particularly in people with clinical anxiety disorders, at a dosage of at least 2000 mg per day. Lower dosages and individuals without clinical diagnoses do not show this effect. Therefore, omega-3 PUFAs could help reduce clinical anxiety symptoms when the dosage is high enough.19
PUFAs may also be beneficial in sports, as omega-3 PUFAs can improve metabolic reactions in skeletal muscle and have anti-inflammatory and antioxidant effects. Furthermore, there is evidence that long-chain omega-3 fatty acids may be helpful in the prevention and treatment of mental disorders.20,21
Despite all this praise, an excess of PUFAs due to poor dietary habits could have negative health consequences. A recently published study analyzed 47 randomized clinical trials (each lasting at least 12 months) with a total of 108,194 participants. The focus was on a possible association between the intake of long-chain omega-3 fatty acids, ALA, omega-6 fatty acids, and total PUFAs and cancer risk. The results showed that an increase in ALA and long-chain omega-3 fatty acids may slightly increase the risk of prostate cancer, while an increased total amount of PUFAs may slightly increase the risk of a cancer diagnosis and death from cancer. However, it must be noted that the increased risk is also associated with slightly protective effects against cardiovascular disease. Nevertheless, even here, "too much of a good thing" can tip the scales.
The following tables show a selection of nuts and seeds that naturally provide dietary fats, including PUFAs. The last table provides an overview of the oils, comparing their PUFA content with other fatty acid components.
Additional information: Fatty acid profile of various nuts, seeds and oils
Fat composition of some nuts, source USDA.23
Order: Amount of polyunsaturated fatty acids (PUFAs) in ascending order, % = proportion of total fat.
Abbreviations: SFA = saturated fatty acids, MUFA = monounsaturated fatty acids, PUFA = polyunsaturated fatty acids. ** = There are practically no Omega-3 PUFAs here, therefore the value of the ratio would be far too low. Meaning of the color: green = LA:ALA ratio below 10:1 and green + bold = LA:ALA ratio below 5:1
Fat composition of some seeds/kernels, source USDA.23
Order: Amount of polyunsaturated fatty acids (PUFAs) in ascending order, % = proportion of total fat
Abbreviations: SFA = saturated fatty acids, MUFA = monounsaturated fatty acids, PUFA = polyunsaturated fatty acids. ** = There are practically no Omega-3 PUFAs here, therefore the value of the ratio would be far too low. Meaning of the color: green = LA:ALA of less than 10:1 and green + bold = LA:ALA of less than 5:1.
Fat composition of some oils, source USDA.23
Order: Amount of polyunsaturated fatty acids (PUFAs) in ascending order, % = proportion of total fat.
Abbreviations: SFA = saturated fatty acids, MUFA = monounsaturated fatty acids, PUFA = polyunsaturated fatty acids, * = not USDA. ** = There are practically no Omega-3 PUFAs here, therefore the value of the ratio would be far too low. Meaning of the color: green = LA:ALA of less than 10:1 and green + bold = LA:ALA of less than 5:1.
Explanation: Why not strictly speaking "100 g" of total fat? This is because oils often contain other components, including trace amounts of vitamins, and primarily lipids (lipids with polar residues – they are similar to fats, but different, as they are not nonpolar like typical fats). Depending on the oil, these lipids can make up to 5 % of the total fat content. Here we provide you with the raw USDA figures, which do not show all nutrients in their entirety.
Absorption and metabolism
ALA and LA undergo mechanical and enzymatic breakdown in the gastrointestinal tract (mouth, stomach, and small intestine) as part of fat digestion. The broken-down fatty acids are transported via micelles into the intestinal cells and from there, bound as lipoproteins, via the blood and lymph to the liver and other target cells such as the brain, heart, and skin.28
Our bodies convert dietary long-chain PUFAs (LA and ALA) into very long-chain unsaturated fatty acids (VLC-PUFAs, VLC = very long chain or HUFA = highly unsaturated fatty acids) through desaturation (desaturase) and elongation (elongase) enzymes. In the case of ALA as the basic substrate, these are: stearidonic acid (18:4, n-3, SDA), docosapentaenoic acid (22:5, n-3, DPA), eicosapentaenoic acid (20:5, n-3, EPA), and docosahexaenoic acid (22:6, n-3, DHA).1
Several factors influence PUFA conversion. For example, the efficiency of ALA to EPA conversion varies between 0,2 % and 21 %, and that of ALA to DHA between 0 % and 9 %, but this is also influenced by competition between LA and ALA.5
Storage - Consumption - Losses
After food intake, enzymes hydrolyze dietary fats in the intestinal lumen. Monoglycerides and free fatty acids produced during hydrolysis integrate into bile salt-containing micelles and enter the enterocytes via passive diffusion. The absorption rate is approximately 95 %. In the intestinal cells, the free fatty acids mainly form chylomicrons and are transported via the lymphatic system into the bloodstream. There, they are metabolized, oxidized, and stored in various tissues.29
Structures
Unsaturated fatty acids are classified according to chain length into three, sometimes four, subgroups (similar to saturated fatty acids). The FAO / WHO expert consultation recommends the following classification:2
Short-chain unsaturated fatty acids: Fatty acids with 19 or fewer carbon atoms.
Long-chain unsaturated fatty acids: Fatty acids with 20 to 24 carbon atoms.
Very long-chain unsaturated fatty acids: fatty acids with 25 or more carbon atoms.
As with monounsaturated fatty acids, the double bond in PUFAs can also exist in cis or trans configuration. In the cis configuration, which is usually predominant in PUFAs, the hydrogen atoms are located on the same side of the double bond, while in the trans configuration they are on opposite sides.3
Conclusion
In Conclusion, both omega-3 and omega-6 PUFAs play a vital role in maintaining the body's equilibrium. They contribute to various cellular activities, such as cell signaling, structural integrity and fluidity of the cell membrane, regulation of blood pressure, glucose levels, the nervous system, inflammatory responses, and blood clotting. Both PUFAs are essential and must be obtained through diet or supplements, as humans cannot synthesize them from precursors like oleic acid. This makes PUFAs the only indispensable fatty acids—unlike saturated (SFA) and monounsaturated fatty acids (MUFA).
Due to poor dietary habits and widespread misinformation about "healthy" foods, we consume the basic PUFAs (namely the omega-3 PUFA alpha-linolenic acid (ALA) and the omega-6 PUFA linoleic acid (LA)) in a very unfavorable ratio, unlike our ancestors. Depending on the country, this ratio is over 20:1 (LA:ALA), although a ratio of 5:1 or less would be ideal. This is because many enzymes (functional proteins) that convert ALA and LA into other PUFAs compete for these basic substances. If there is a significant excess of LA, its byproducts are much more prevalent in the body. Excess omega-6 PUFAs produce lipid mediators, which are associated with narrowing of the blood vessels, inflammation, and platelet aggregation (clumping of blood platelets), while omega-3 PUFAs have the opposite effect and can even have positive health benefits (see the subsection above). It is therefore important to pay attention to a balanced PUFA ratio in your diet. Even reducing LA intake helps to increase omega-3 PUFA levels in the body. The goal is to consume more omega-3 fats, fewer omega-6 fats, and fewer calories per meal.
Consuming unfavorable foods high in omega-6 fatty acids (e.g., cashews, sweet almonds, pistachios, and peanuts), processed foods (too many SFAs and artificial additives), or oils particularly high in lactic acid (LA) such as sesame oil, sunflower oil, coconut oil, or palm oil can harm our bodies in the long run. It would be better to reduce their consumption and increase our intake of omega-3 fatty acids, which are found in flaxseeds, chia seeds, hemp seeds, and tree nuts, among other sources. The tables at the top of this article can help you gain an overview of the PUFAs and the LA:ALA ratio in particularly high-fat foods. This allows you to adjust your eating habits by reducing or even replacing foods with a very high omega-6 fatty acid content or a particularly unfavorable LA:ALA ratio.
In certain cases (e.g., declining metabolic function in older individuals), additional intake of omega-3 PUFA supplements can be beneficial (especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)). Considering overfishing, vegan lifestyles, and risk groups for heavy metal exposure (children, pregnant women, etc.), supplementation in the form of purified algae oil can be a suitable option. However, even though there are many recent studies on the positive effects of omega-3 PUFAs, one should not overdo it with artificial supplements. Some studies have also indicated a slightly increased risk of cancer from excessively high doses of omega-3 PUFAs over a period of 12 months or longer, in addition to the numerous health benefits. Ultimately, as is so often the case, a healthy balance based on natural ingredients is the best medicine we can provide.
Bibliography - 30 Sources
Many researchers do not believe that Wikipedia is an authoritative source. One reason for this is that the information about literature cited and authors is often missing or unreliable. Our pictograms for nutritional values provide also information on calories (kcal).
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