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  #1   ^
Old Fri, Sep-18-15, 13:26
teaser's Avatar
teaser teaser is offline
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Default Inuit adaptation to high omega 3 fats

http://www.sciencedaily.com/release...50917160034.htm

Quote:
Adaptation to high-fat diet, cold had profound effect on Inuit, including shorter height
Greenlanders developed unique mutations to deal with diet high in omega-3 fatty acids


Quote:
The traditional diet of Greenland natives -- the Inuit (once known as Eskimos) -- is held up as an example of how high levels of omega-3 fatty acids can counterbalance the bad health effects of a high-fat diet, but a new study hints that what's true for the Inuit may not be true for everyone else.

The study, which appears in the Sept. 18 issue of the journal Science, shows that the Inuit and their Siberian ancestors have special mutations in genes involved in fat metabolism that help them partly counteract the effects of a diet high in marine mammal fat, mostly from seals and whales that eat fish with high levels of omega-3 polyunsaturated fatty acids.

Those genetic mutations, found in nearly 100 percent of the Inuit, are found in a mere 2 percent of Europeans and 15 percent of Han Chinese, which means they would synthesize omega-3 polyunsaturated fatty acids differently from the Inuit.

"The original focus on fish oil and omega-3s came from studies of Inuit: on their traditional diet, rich in fat from marine mammals, Inuit seemed quite healthy with a low incidence of cardiovascular disease, so fish oil must be protective," said project leader Rasmus Nielsen, a UC Berkeley professor of integrative biology. "We've now found that they have unique genetic adaptations to this diet, so you cannot extrapolate from them to other populations. It could be very good for the Inuit to eat all these omega-3 fatty acids, but not for the rest of us."

These genetic mutations in the Inuit have more widespread effects. They lower "bad" LDL cholesterol and fasting insulin levels, presumably protecting against cardiovascular disease and diabetes. They also have a significant effect on height, because growth is in part regulated by a person's fatty acid profile. The researchers found that the mutations causing shorter height in the Inuit are also associated with shorter height in Europeans.

"The mutations we found in the Inuit have profound physiological effects, changing the whole profile of fatty acids in the body, plus it reduces their height by 2 centimeters: nearly an inch," said Ida Moltke, a University of Copenhagen associate professor of bioinformatics who is joint first author on the study. "Height is controlled by many genes, but this mutation has one of the strongest effects on height ever found by geneticists."

Personalized diets

Nielsen noted that this is the first evidence that human populations are actually adapted to particular diets; that is, they differ in the way they physiologically respond to diets. Just as genome sequencing can lead to personalized medicine tailored to an individual's specific set of genes, so too may a person's genome dictate a personalized diet.

"People ask themselves whether they should be on a stone-age diet, for example. The response may well depend on their genome," Nielsen said.

Nielsen and his colleagues at UC Berkeley and in Greenland and Denmark came to their conclusions after analyzing the genomes of 191 Greenlanders with a low admixture of European genes (less than 5 percent) and comparing them to the genomes of 60 Europeans and 44 Han Chinese. They looked for mutations occurring in a large percentage of Inuit individuals but in few or no other groups, which indicates that the mutation spread throughout the Inuit because it was somehow useful to their survival while not essential in other groups.

One cluster of mutations -- in genes that code for enzymes that desaturate carbon-carbon bonds in fatty acids -- stood out strongly, said Anders Albrechtsen, an associate professor of bioinformatics at the University of Copenhagen and a joint project leader. Fatty acids are the fat in our diet, and occur in saturated, polyunsaturated and unsaturated forms depending on whether the molecules' carbon atoms are linked together with no, some or all double bonds. Saturated fats are considered bad because they raise levels of cholesterol and low density lipoproteins (LDL) in the blood and lower the 'good' high density lipoproteins (HDL), all of which lead to plaque formation and clogged arteries. Diets rich in polyunsaturated and unsaturated fats are linked to lower heart disease. Desaturase enzymes convert dietary fatty acids into fatty acids stored and metabolized by the body.

The mutations common in the Inuit, once known as Eskimos, downregulate the production of both omega-3 and omega-6 polyunsaturated fatty acids, presumably to account for the high amount of these fatty acids coming from the diet. Changing production of one fatty acid affects all fatty acids, however, since they regulate one another in a complex way, Albrechtsen said.

Thus, while it's not clear which specific gene or genes within the cluster is responsible for the alteration in fatty acid metabolism, he said that "when you change the genes that are involved in fatty acid synthesis, you change the whole conversation among fatty acids, and that has a lot of downstream effects."

Adaptation to Ice Age living

The mutations seem to be at least 20,000 years old, and may have helped many groups of humans adapt to high-meat, high-fat, hunter-gatherer diets from large land and marine mammals high in certain types of omega-3 and omega-6 fatty acids, says Matteo Fumagalli, a researcher at University College -- London, who is joint first author of the study. They may have arisen among the original Siberians, who have lived in the Arctic for more than 20,000 years, and arrived in Greenland when Inuit settled there about 1,000 years ago.

"We think it is a quite old selection that may have helped humans adapt to the environment during the last Ice Age, but the selection is far stronger in the Inuit than anywhere else," said Fumagalli. "It's fascinating that Greenlanders have a unique genetic makeup that lets them better use their traditional food sources."

The researchers discovered another common mutation in a gene that is involved in the differentiation of brown, subcutaneous fat cells and brite fat cells, the latter of which generate heat. This may also have helped the Inuit adapt to a cold environment.


Quote:
The traditional diet of Greenland natives -- the Inuit (once known as Eskimos) -- is held up as an example of how high levels of omega-3 fatty acids can counterbalance the bad health effects of a high-fat diet, but a new study hints that what's true for the Inuit may not be true for everyone else.


And other studies at least hint that a high fat diet, in and of itself, high in omega 3 or no, might not be something we need protecting from.

As usual the write-up goes beyond the scope of the actual finding.

Anyways... looks like a pretty straightforward loss-of-function sort of mutation. Maybe not straightforward in the details. If your ancestors for 20000 years or so were able to get all the dha, epa, arachidonic acid etc. they needed straight from the diet, rather than having to produce them in-house from linoleic or alpha-linolenic acid, what's the point of keeping the machinery needed for that production intact? Is this an adaptation, to allow them to cope with eating a marine-based diet--or the loss of the ability to deal with a diet that doesn't contain pre-formed dha, epa, and arachidonic acid?
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  #2   ^
Old Fri, Sep-18-15, 18:13
MickiSue MickiSue is offline
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Taubes goes into detail, in GCBC, about a group of explorers who lived with the Inuit for several years, eating their traditional diet, and suffered no ill effects. On the contrary, they remained extraordinarily healthy.

When they returned to the US, and the paper written on the years in the extreme north was reviewed, one reviewer noted that it was easier to believe that the authors were lying, than that they really could thrive on meat alone.

So two members of the expedition subjected themselves to an experiment at Columbia Presbyterian Hospital. By the time of the experiment, they'd been eating a typical American diet for about a year. They both went inpatient, under 24 hour surveillance, after having baseline lab work done.

For weeks, eating only meat and fat, they were watched. Labs were drawn regularly, so that the new baselines on a meat only diet could be found.

Then they were released, but continued to eat only meat and fat for a year. They continued their regular lab work.

At the end of the year, both of them, having begun the experiment at a normal weight, had lost a few pounds. Their cardiovascular labs were better, and one of them, who'd had low level gingivitis at the start of the year, no longer had it.

The study that you note is going back to the belief from before that expedition: that it must be some particular genetic adaptation that allows societies to eat no vegetable matter, and yet, stay healthy. This one is a new spin on it.

None of the researchers in that group were Inuit. The last name of the leader of the expedition (which I can't remember) was Scandinavian.
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  #3   ^
Old Fri, Sep-18-15, 20:03
teaser's Avatar
teaser teaser is offline
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Steffanson.

This reminds me of the low salivary amylase thing among Inuit. Another adaptation that really doesn't increase the ability to live on a meat-based diet--just reduces the ability to live on a plant-based diet.

Peter talks here about another common adaptation among Inuit that's a bit harder to explain;

http://high-fat-nutrition.blogspot....-in-arctic.html

Quote:
The paper itself is largely an account of the detective work involved in pinning down a specific mutation which has been positively selected for in a Siberian population living in the Arctic. The same mutation is also present in non related groups inhabiting the Arctic areas of northern America. The mutated gene is very common and frequently homozygous. It puts a leucine in the place of a proline in CPT-1a, the core enzyme for getting long chain fatty acids in to mitochondria. Putting a leucine where there should be a proline means the protein is basically f*cked. The mutation is linked, not surprisingly, to failure to generate ketones in infancy and can be associated with profound hypoglycaemia, potentially causing sudden death.


Seems a little weird that people in the Arctic should have an adaptation that makes ketosis difficult...

One possibility that just came to mind--many animals in the Arctic are fairly insulin resistant. This preserves scarce glucose. Human milk is fairly high in carbohydrate.

Most small children slip easily in and out of ketosis, on a regular basis. Perhaps a more conservative carbohydrate metabolism preserves glucose for the brain, making this ketosis less necessary? This would explain an adaptation that decreases ketone production as an adaptation only possible because of another adaptation to a near total lack of carbohydrate in the diet.
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  #4   ^
Old Fri, Sep-18-15, 20:46
MickiSue MickiSue is offline
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Heh. I knew you'd know his name, Teaser.

And that is the reason I think this "new" finding is bunk. It's just an attempt to retrofit the facts to fit the theory that "too much" fat is bad for (most) humans.
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  #5   ^
Old Fri, Sep-18-15, 21:59
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Nicekitty Nicekitty is offline
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Quote:
Nielsen noted that this is the first evidence that human populations are actually adapted to particular diets; that is, they differ in the way they physiologically respond to diets. Just as genome sequencing can lead to personalized medicine tailored to an individual's specific set of genes, so too may a person's genome dictate a personalized diet.


Ooh, I think I figured out how to quote "box" stuff finally! Learn something new every day.

I find this stuff fascinating. It only makes sense that humans, living for the vast majority of time in very disparate places, with very different diets, would develop or lose mutations to give them an adaptive advantage. Hopefully a continued study of genetics can help us begin to unravel some of these genetic differences. Of course we are so mixed up, unless we have a personalized genetic evaluation, the information may not help us determine the "ideal diet".
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