Omega-3: conversion of ALA into EPA and DHA

In the previous article, I wrote about the benefits of four types of omega-3: docosahexanoic acid (DHA), eicosapentanoic acid (EPA), alpha-linolenic acid (ALA) and stearidonic acid (SDA). DHA and EPA can be found in certain fatty fishes and microalgae (more on this in the next article), while ALA and SDA can be obtained from certain seeds (check our last article for more details on that).

As explained in the last article, in our body, the plant-based omega-3 fatty acids ALA and SDA can be converted to EPA and DHA. But to what extent does this conversion occur? Well, it is not that simple and it depends on many factors. So, let’s take a look at the current state of scientific research on the topic.

 

Conversion of ALA and SDA into EPA

Many studies have shown that an increased ALA consumption leads to an increased blood EPA concentration, as reviewed in [1]. It is estimated that the rate of conversion of ALA into EPA in the liver is about 21% in women and between 0.3% and 8% in men [1, 2].

As I wrote in the last article, studies show that SDA intake results in an even higher EPA concentration than ALA intake [3, 4], which is quite interesting.

Since EPA has been related to anti-inflammatory benefits, it seems that plant-derived omega-3 fatty acids have a high potential to reduce inflammation and to protect against chronic inflammatory diseases [2, 5], such as rheumatoid arthritis.

 

Conversion of ALA and SDA into DHA

While an increase in EPA with increased ALA or SDA consumption is consistent among studies, this is not as clear when it comes to DHA. The rate of conversion of ALA into DHA lies somewhere between <1% and 9% [1, 6, 7]. This conversion occurs in the liver and, in a smaller extent, in the brain as well [7]. However, many studies report little or no change in DHA levels with increased ALA or SDA consumption [1, 3, 4], but this depends on many factors, which might explain the differences found between studies, namely:

gender:  the rate of conversion from ALA to DHA is higher in women of reproductive-age than in men, which may be due to a regulatory effect of estrogen  [1, 8]. This is important for pregnancy and lactation given that DHA is crucial for the developing brain. However, a study in pregnant women found that supplementation with ALA significantly increased maternal and neonatal EPA, but not DHA [9]. However, they argued that maybe additional DHA was indeed produced from the supplemented ALA, but it was transferred directly to the fetus and, therefore, did not increase the maternal DHA concentration [9]. This was further supported by a higher functional DHA status in infants of ALA-supplemented mothers in that study.

infants: studies suggest that the conversion of ALA into DHA may be more efficient in infants than in adults, where the higher the amount of consumed ALA, the higher the DHA concentrations [2, 10, 11]. These studies suggest that infants have a greater capacity to convert ALA to DHA than adults, probably because it is a critical development period as omega-3 fatty acids are required for rapid growth of neural tissues. But there is a high variability among human infants in the development of the capability to convert ALA to DHA [12]. However, there might be situations in which the DHA synthesis from ALA might not be enough. For example, it seems that breastfed infants have higher brain DHA concentrations than infants fed formulas containing ALA but not DHA [7].

I would like to mention that the conversion of ALA into DHA has not really been studied across other age subgroups of the population including children, adolescents, pregnant and lactating women, and the elderly.

DHA intake: people who consume DHA have a lower rate of conversion of ALA into DHA, or even no conversion at all [7, 13]. The body is intelligent and knows that in this situation you don’t really need that extra effort of producing DHA given that you are already taking it.

linoleic acid (LA) intake: as explained in the last article, LA is a omega-6 fatty acid that competes for the same enzymes as the omega-3 fatty acids. An increased LA intake might decrease the conversion of ALA into EPA in humans [14] and it has been argued that exchanging dietary LA for ALA may be an important dietary approach to increase EPA and DHA status [15]. I want to add though, that in opposition to what many people think, you do need omega-6 as well as omega-3. Ideally, you would eat a ratio 1:1 omega-6 to omega-3. But what is happening nowadays is that people tend to eat much more omega-6 due to high consumption of vegetable oils.

being vegan or vegetarian: in vegetarians, ALA supplementation increases the concentration of EPA, but not DHA [16]. However, in vegans, the evidence is different. In an interesting study, it was found that although DHA intake by vegans was zero, they still had DHA present in blood phospholipids, even if lower than in fish-eaters [13]. Furthermore, they found that the rate of conversion of ALA into DHA was twice as high in vegans than in fish-eaters [13]. This suggests that this conversion is much higher in the absence of dietary DHA and that our body has an amazing capacity to adapt to its needs. Indeed, vegetarian and vegan diets have been associated with lower but stable plasma phospholipid DHA fatty acid concentrations [17]. And it seems that in spite of having lower DHA blood concentrations, there is no evidence whatsoever of lower cognitive function or other neurological problems in vegans [7, 16]. Therefore, it seems that in healthy individuals, this low synthesis is still enough to meet our brain DHA requirements, as reviewed by Domenichiello and colleagues in 2015 [7]. They state:

“Vegetarians and vegans, in which DHA derived from ALA is the sole source of DHA, have plasma DHA levels that are 0–40% lower than omnivores and have neurological disease rates comparable to omnivores suggesting that ALA-derived DHA is sufficient to maintain brain function in these individuals. In addition, dietary ALA, with no DHA, is sufficient to completely restore brain DHA in rats and non-human primates.”

However, it is still not known whether enhanced brain performance could be achieved or even future neurological disorders could be prevented with increased DHA levels in vegans and vegetarians. Also, if vegans would like to ensure that their DHA levels are the same as fish eaters “just in case”, a plant-based omega-3 supplement would be useful as well as checking their blood omega-3 status. Please check our next article for more information on omega-3 supplements and on this omega-3 testing.

This was for the brain. What about the heart? Given that EPA and DHA are also very important for the heart, do vegetarians and vegans have an increased risk of cardiovascular diseases? Well, no – quite the opposite: they actually have a reduced risk of cardiovascular diseases [18]. However, as for the brain, there is no data until now addressing whether cardiovascular risk in vegetarians could be even lower with higher omega-3 concentrations.

– eating turmeric: very interestingly, a study in rats has shown that when ALA or curcumin were consumed alone, there was no increase in brain DHA content, however, the combined intake of ALA and curcumin led to an increase in brain and liver DHA content as well as the enzymes needed for the conversion of ALA into DHA! [19] The authors state:

These findings suggest that curcumin may enhance the conversion of ALA to DHA in vivo and elevate DHA content in brain.

As the authors note, this finding could be especially important for people who do not consume fish regularly, such as vegetarians and vegans. As also noted in the study, turmeric is a staple in the Indian cuisine, while fish is not, as some part of the Indian population mainly eats vegetarian. And in spite of that, they don’t seem to have more neurological disorders than the rest of the population. Interestingly, another study by the same authors showed that curcumin and DHA combined can be a useful complementary treatment to counteract neuronal dysfunction in traumatic brain injury [20].

Now, you may be asking: what if we increase ALA consumption, will our DHA also increase? Well, research has been saying no. It seems that an increase of ALA intake does not correlate linearly to an increase in DHA – some studies show no difference in plasma or cell membrane DHA concentration after an increased ALA intake [21]. I found it interesting that in rats, the synthesis of DHA from ALA seems not to be altered by ALA deprivation – the conversion rate with ALA in the diet or not was the same, suggesting that the body tries to keep brain DHA levels constant [6]. However, it is not known for how long this could be sustained in humans. So, if you do not eat regularly fish or are not taking DHA supplements, I really think that you should make sure you consume enough ALA daily (ideally from a whole food source, such as flax seeds, hemp seeds, chia seeds or walnuts) and if possible together with turmeric. If you do take a DHA supplement, I still believe that you should be eating everyday an ALA-rich food, as it has many benefits for us as explained in the previous article.

 

So, take-home messages from this article:

-the conversion of ALA and SDA into EPA is consistent among studies

-the rate of conversion of SDA into EPA is even higher than the one of ALA into EPA

-the rate of conversion of ALA into DHA is lower than the conversion of ALA into EPA, and it is not consistent among studies

-this lack of consitency might be due to several factors influencing the conversion of ALA into DHA

-the conversion of ALA into DHA is higher in:

  • women of reproductive age
  • infants
  • people who do not consume DHA
  • people who consume a low amount of LA omega-6
  • vegans
  • and possibly, when we consume ALA together with turmeric

-an increased ALA consumption does not seem to raise DHA levels, but this could depende on the several factors mentioned above.

So, for some people, it seems that the conversion from ALA to DHA occurs and is enough to mantain brain function. However, there might be situations in which EPA and DHA supplementation can be beneficial. In the next article, I will write about the pros and cons of three types of omega-3 supplements, so that you can make an informed choice if you chose to take an EPA and DHA supplement. I will also tell you why nowadays fish intake is not an ideal source of omega-3, from both a health and environmental point of view.

If you have any question regarding this topic, you can write a comment below! I will try to answer them as good as I can 🙂

 

Live healthy,

Ana

 

References

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  2.         Baker, E.J., et al., Metabolism and functional effects of plant-derived omega-3 fatty acids in humans. Prog Lipid Res, 2016. 64: p. 30-56.
  3.         James, M.J., V.M. Ursin, and L.G. Cleland, Metabolism of stearidonic acid in human subjects: comparison with the metabolism of other n-3 fatty acids. Am J Clin Nutr, 2003. 77(5): p. 1140-5.
  4.         Walker, C.G., S.A. Jebb, and P.C. Calder, Stearidonic acid as a supplemental source of omega-3 polyunsaturated fatty acids to enhance status for improved human health. Nutrition, 2013. 29(2): p. 363-9.
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  6.         Igarashi, M., et al., Docosahexaenoic acid synthesis from alpha-linolenic acid by rat brain is unaffected by dietary n-3 PUFA deprivation. J Lipid Res, 2007. 48(5): p. 1150-8.
  7.         Domenichiello, A.F., A.P. Kitson, and R.P. Bazinet, Is docosahexaenoic acid synthesis from alpha-linolenic acid sufficient to supply the adult brain? Prog Lipid Res, 2015. 59: p. 54-66.
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  9.         de Groot, R.H., et al., Effect of alpha-linolenic acid supplementation during pregnancy on maternal and neonatal polyunsaturated fatty acid status and pregnancy outcome. Am J Clin Nutr, 2004. 79(2): p. 251-60.
  10.       Sauerwald, T.U., et al., Effect of dietary alpha-linolenic acid intake on incorporation of docosahexaenoic and arachidonic acids into plasma phospholipids of term infants. Lipids, 1996. 31 Suppl: p. S131-5.
  11.       Jensen, C.L., et al., Biochemical effects of dietary linoleic/alpha-linolenic acid ratio in term infants. Lipids, 1996. 31(1): p. 107-13.
  12.       Brenna, J.T., Efficiency of conversion of alpha-linolenic acid to long chain n-3 fatty acids in man. Curr Opin Clin Nutr Metab Care, 2002. 5(2): p. 127-32.
  13.       Welch, A.A., et al., Dietary intake and status of n-3 polyunsaturated fatty acids in a population of fish-eating and non-fish-eating meat-eaters, vegetarians, and vegans and the product-precursor ratio [corrected] of alpha-linolenic acid to long-chain n-3 polyunsaturated fatty acids: results from the EPIC-Norfolk cohort. Am J Clin Nutr, 2010. 92(5): p. 1040-51.
  14.       Bradbury, J., Docosahexaenoic acid (DHA): an ancient nutrient for the modern human brain. Nutrients, 2011. 3(5): p. 529-54.
  15.       Goyens, P.L., et al., Conversion of alpha-linolenic acid in humans is influenced by the absolute amounts of alpha-linolenic acid and linoleic acid in the diet and not by their ratio. Am J Clin Nutr, 2006. 84(1): p. 44-53.
  16.       Arterburn, L.M., et al., Bioequivalence of Docosahexaenoic acid from different algal oils in capsules and in a DHA-fortified food. Lipids, 2007. 42(11): p. 1011-24.
  17.       Rosell, M.S., et al., Long-chain n-3 polyunsaturated fatty acids in plasma in British meat-eating, vegetarian, and vegan men. Am J Clin Nutr, 2005. 82(2): p. 327-34.
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  19.       Wu, A., et al., Curcumin boosts DHA in the brain: Implications for the prevention of anxiety disorders. Biochim Biophys Acta, 2015. 1852(5): p. 951-61.
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