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The Effect of Diet Changes and The Selection of European Fatty Acid Desaturases

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UC Berkeley Integrative Biologist, Rasmus Nielsen and his colleagues, published a fascinating study in the journal Molecular Biology and Evolution looking at hundreds of human genomes and the relative diets. They were even able to include the genomes of 101 Europeans from 5,000 years ago, during the Bronze Age as well as Neanderthals and Denisovan genes. The authors compared all these genomes, they found that two particular regions of DNA were under intense selection over the past several thousand years and changed rapidly in response to evolutionary pressures.

These two regions encode for two enzymes, fatty acid desaturase 1 and 2, or FADS1 and 2 for short. The FADS enzymes are known to regulate the conversion of short-chain poly-unsaturated fatty acids into long-chain PUFAs. Those FADS genes of Europeans dating back to the Bronze Age underwent mutations to produce to convert long-chain PUFAs compared to Neanderthals and other ancient humans. This suggests they sustained a new diet higher in vegetables and grains, which give short-chain PUFAs but need to be converted to long-chain PUFAs. Meat, on the other hand, provides long-chain PUFAs.

The genomes of northern Europeans, including Inuits, have FADS genes that convert fewer long-chain PUFAs, likely because their diets are already high in animal fats. Southern Europeans are optimized for a high-plant diet, resulting in a lower intake of arachidonic acid and eicosapentaenoic acid, but a higher intake of linoleic acid and α-linolenic acid. But people from other areas, such as Greenlander, have a biochemistry that is better able to process lots of meat fat.

Nielsen hypothesis that the observed gradient in FADS genes are the result of the agricultural revolution. The dawn of agriculture, approximately 10,000 years ago, farmers provided food which lead to diets rich in wheat and vegetables. Suddenly, the human diet had diets higher in short-chain PUFAs and those who could convert short-chain PUFAs into long-chain PUFAs more efficiently were more likely to survive, and so their FADS genes were passed on.

Nielsen also examined FADS variants in Neanderthal and Denisovan genes. 40,000 years ago, FADS genes were a selective target in these ancient humans just as they are now. This suggests that either FADS variants pre-date the divergence of modern humans and Neanderthals or modern humans and Neanderthals both inherited the genetic variants by introgression with another undetermined species.

The FADS genes have continued rapidly changing as humans found new environmental niches across the planet, a stark contrast to the genetics of lactose tolerance. Lactose tolerance, or persistence of the lactase gene, as we all know is stronger among Northern Europeans who relied less on the agricultural revolution and domestication — something we would expect to see more prevalent amongst Southerners… Implying there is little overlap between people with veggie-friendly FADS genes and people with genes for lactase persistence.

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