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Omega-3 Mystery Solved?
Most people need fish to fully thrive, but some don’t; Answer may lie in “green” genes

04/06/2016 By Craig Weatherby
Surprising findings call conventional wisdom about omega-3s into question.

But they don't reduce the importance of seafood-source omega-3s for the vast majority of people.

In fact, most Americans don't get enough of them … see Omega-3 Deficiency May Cause 84,000 Premature Deaths.

Before we explore the new findings, we'll describe the critically important context in which they occur. 

Then we'll recap evidence that vegetarians make especially good of plant-source omega-3s ... findings explained by the results of new research that detected "green" genes in some people.

Background to the study: Omega-3 basics
The human body needs two kinds of omega-3s to survive and thrive – DHA and EPA – which are found only in seafood.

However, humans shouldn't need seafood to survive, because we can convert the sole plant-source omega-3 (ALA) into omega-3 DHA and EPA.

But the standard American diet is extremely overloaded with omega-6 fatty acids from vegetable oils and other plant foods.

That omega-6 overload greatly reduces your body's ability to convert plant source omega-3 ALA into the omega-3 DHA and EPA you actually need.

This very common omega-6 overload explains why most Americans need seafood-source omega-3s (DHA and EPA) to avoid chronic health problems and fully thrive.

First clues to the mystery: Vegetarians get more out of plant-source omega-3s
It's recently become clear that – despite eating little or no seafood – some people enjoy good health.

The first signs came from British studies which found that longtime vegetarians and vegans convert plant source omega-3s into DHA and EPA more efficiently, compared with people who eat seafood regularly … see Fish-Avoiders Have More Omega-3s than Expected.

Those findings found support from the results of an international study published four years ago: see Dramatic Omega-3 Discovery: Genes Matter.

The scientists behind that 2012 study discovered that peoples' genetic profiles greatly influence the fate and impact of the omega-3 and omega-6 fatty acids they consume. 

It turns out that people who possess a gene variant called haplotype D can more easily convert plant-source omega-3 ALA into the seafood-type omega-3s (DHA and EPA) we actually need.

That gene variant is commonly found in Africa, South Asia (the Indian subcontinent), and certain parts of the Middle East, making those people less reliant on seafood.

In contrast, people who possess the gene variant called haplotype A produce relatively small amounts of omega-3 DHA and EPA from the omega-3 ALA in plant foods.

The haplotype A variant is very common among people in North and South America … which means that they need to do one of two things to fully thrive:
  • Eat seafood – especially fatty fish, which is rich in omega-3 DHA and EPA.
  • Strictly limit their intake of omega-6 fats and get plenty of plant-source omega-3s.
In short, that study found that the health value of omega-3 ALA from plant foods depends heavily on your geographic and/or ethnic background.

And that difference probably stems from your ancestors' adaptation to the diets typical of their heritage. Now, an international study adds weight and detail to those findings.

The new findings: "Green" genes help some people thrive without seafood
The new study, which involved researchers from several countries, was led by Cornell University scientists (Kothapalli KS et al. 2016).

They discovered a gene variation – also called an allele – that evolved in regions where vegetarian diets are common … such as India, Africa, and parts of East Asia.

This so-called "green"  allele enables people whose ancestors ate little or no seafood to efficiently convert ALA – the plant-source omega-3 – into DHA and EPA ... the only omega-3s essential for brain, visual, and immune functions (e.g., controlling inflammation).

Presence of the "green" gene allele varies geographically, reflecting the dominance of plant-based diets, versus diets based on animal foods, including seafood:
  • 68 percent of Indians
  • 70 percent of all South Asians
  • 53 percent of Africans
  • 29 percent of East Asians
  • 18 percent of Americans 17 percent of Europeans

In populations that have been eating plant-based diets for many generations, this genetic variation provided an advantage that was favored by natural selection.

Put another way, people eating plant-based diets who had the "green” gene variation were more likely to survive and bear healthy children.

The researchers are not sure yet when this adaptation first occurred, but there's evidence for the allele in the genomes of early hominids, including Neanderthals and Denisovans.

"Mirror-image” seafood gene found in native Greenlanders
You might expect that populations who've eaten seafood over many generations would have adapted to that diet … and you'd be right.

The researchers discovered a mirror image of the "green”, vegetarian-type allele among the native Inuit people of Greenland, whose genes have adapted to a seafood-rich diet over time.

As a result, the Inuit – and other ethnic groups that eat lots of seafood – have greater difficulty converting plant source omega-3s (ALA) into the omega-3 DHA and EPA our bodies actually need.

According to study co-author Kaixiong Ye, "… when people migrated to different environments, sometimes they ate a plant-based diet and sometimes they ate a marine-based diet, and in different time periods these different alleles were adaptive.”

In plain English, this means that people's alleles have a tendency to evolve under dietary pressures.

The study was funded by the National Institutes of Health and the U.S. Department of Agriculture.

A more nuanced picture of omega-3s in human health
This finding marks a genuine revolution in our understanding of the role of seafood in human health.

It means that – in theory – people in large parts of the globe do just fine with little or fish or shellfish.

However, that holds true only if their diets aren't overloaded with competing omega-6 fats from plant foods.

Unfortunately, that omega-6 overload is beginning to plague populations worldwide, thanks to the recent availability of cheap vegetable oils high in in omega-6 fats: primarily soy, corn, cottonseed, safflower, and sunflower oils.

(The exceptions are "high oleic” versions of safflower and sunflower oil, which are low in omega-6s. These are much more common in the U.S. than in less-developed countries).

So while some ethnic groups should have much less need for seafood, their ability to rely on plant-source omega-3s is threatened by increasing consumption of plant-source omega-6 fats worldwide.

The implication of increasing omega-6 consumption is that everyone – even people with the "green” allele – can benefit from eating more seafood.


Sources
  • Abdelmagid SA, Clarke SE, Roke K, Nielsen DE, Badawi A, El-Sohemy A, Mutch DM, Ma DW. Ethnicity, sex, FADS genetic variation, and hormonal contraceptive use influence delta-5- and delta-6-desaturase indices and plasma docosahexaenoic acid concentration in young Canadian adults: a cross-sectional study. Nutr Metab (Lond). 2015 Apr 21;12:14. doi: 10.1186/s12986-015-0010-9. eCollection 2015.
  • Ameur A et al. Genetic Adaptation of Fatty-Acid Metabolism: A Human-Specific Haplotype Increasing the Biosynthesis of Long-Chain Omega-3 and Omega-6 Fatty Acids. The American Journal of Human Genetics (2012). doi:10.1016/j.ajhg.2012.03.014. Published online April 12, 2012.
  • Cornell University/Ramanujan K. Eating green could be in your genes. March 29, 2016. Accessed at http://www.news.cornell.edu/stories/2016/03/eating-green-could-be-your-genes
  • Kothapalli KS et al. Positive selection on a regulatory insertion-deletion polymorphism inFADS2influences apparent endogenous synthesis of arachidonic acid. Molecular Biology and Evolution, 2016; msw049 DOI: 10.1093/molbev/msw049. Accessed at http://mbe.oxfordjournals.org/content/early/2016/04/04/molbev.msw049
  • Merino DM, Johnston H, Clarke S, Roke K, Nielsen D, Badawi A, El-Sohemy A, Ma DW, Mutch DM. Polymorphisms in FADS1 and FADS2 alter desaturase activity in young Caucasian and Asian adults. Mol Genet Metab. 2011 Jun;103(2):171-8. doi: 10.1016/j.ymgme.2011.02.012. Epub 2011 Feb 23.
  • Zhang JY, Kothapalli KS, Brenna JT. Desaturase and elongase-limiting endogenous long-chain polyunsaturated fatty acid biosynthesis. Curr Opin Clin Nutr Metab Care. 2016 Mar;19(2):103-10. doi: 10.1097/MCO.0000000000000254.