The hottest topic in medical research may be the human “microbiome”.

The term microbiome means the collection of bacteria and other microbes in your gut and mucous membranes.

Much remains mysterious about how the microbiome affects health, but there's no doubt it has profound impacts, for good or ill. 

See “The Culture War in Your Gut”, which includes links to our past coverage of this topic. 

We're told that the lactobacilli bacteria in yogurt and lacto-fermented foods – like acidophilus and Bifidobacterium – foster a “healthy” microbiome, and there's evidence for that assertion.

But it isn't clear that we need lactobacilli – versus other strains – to keep bad bugs in check in our bodies … see “There Is No ‘Healthy' Microbiome”, in The New York Times.

Now, the results of two studies in mice suggest that omega-3 and omega-6 fatty acids can affect gut health in major ways.

Prior research showed that dietary choices and certain microbes in the gut can promote or help prevent inflammatory bowel disease (IBS), colitis (inflammation of the colon), and Crohn's disease.

In particular, polyunsaturated fats are known to affect the microbes living in the intestines … known as the “gut microbiota.”

The new animal research suggests that the two major kinds of polyunsaturated fat – omega-3 and omega-6 – impact our microbiomes for the better (omega-3s) or worse (omega-6 fats in excess).

And one of the new studies found that the best microbiome effects were seen in mice fed a diet high in saturated fats that also received supplemental omega-3s.

Both studies were presented at the 11th Congress of the International Society for the Study of Fatty Acids and Lipids (ISSFAL) in Stockholm.

Study #1 - Omega-3s helped metabolic health by improving the microbiome
The first study came from Harvard Medical School and Massachusetts General Hospital.

Eight years ago, a team led by Jing X. Kang, M.D., Ph.D. published the first evidence showing that mice genetically altered to produce omega-3s from omega-6 fats –  something neither mice nor men can normally do – enjoyed protection from colitis (Hudert CA et al. 2006).

In another prior study, Dr. Kang's team studied the metabolisms of mice genetically altered to internally produce omega-3s from omega-6 fats.

This genetic tweak led to two key benefits: increased calorie-burning and less inflammation.

As Dr. Kang's team wrote, by raising omega-3 levels and reducing omega-6 levels, this genetic modification in mice produced changes that “... strongly protect against obesity, diabetes, inflammation, and dyslipidemia and may represent a novel therapeutic modality to treat these prevalent disorders.” (Li J et al. 2014)

More recently, Dr. Kang's group conducted a mouse study showing that diets low in omega-6 fats and high in omega-3 fats were beneficial to the gut microbiome.

This diet reduced harmful bacteria, while fostering larger colonies of beneficial bacteria … changes that led to less inflammation.

As Dr. Kang pointed out, “Chronic low-grade inflammation contributes to the development of many chronic diseases and can be induced by harmful gut microbiota.” 

“Therefore, dietary strategies that lower the omega-6/omega-3 [intake] ratio … such as reducing intake of vegetable oils, processed foods, and grain-raised livestock high in omega-6 fat and increasing intake of fish and green vegetables – could prove effective for managing such diseases.” 

And he noted that fish oil could be as good as fish: “For management of certain [gut-centered] health conditions, a high quality, concentrated omega-3 supplement is also practical.” (ISSFAL 2014)

Study #2 - Omega-3s protected mice against colitis and related gut problems
The second study came from the University of British Columbia, Canada, where scientists examined the effects of omega-3 and -6 fats in mice infected with a bacteria that causes colitis.

Last year, this same research team found that diets rich in omega-6 fats caused “dysbiosis” in mice … in other words, this diet altered the animals' microbiomes in ways that promote inflammation and overgrowth of disease bacteria (Ghosh S et al. 2013).

In the new study, mice fed diets high in omega-6 fats (from corn oil) suffered damage to their intestines and immune cells, and overgrowth of harmful bacteria (Ghosh S et al. 2014).

On the other hand, diets high in seafood-source omega-3s (EPA and DHA) produced higher levels of microbes that dampen inflammationwhich reduced immune cell damage and inflammation while preventing the damage caused by colitis.

And the researchers made another, unexpected discovery that seems to favor Paleo diets that include ample amounts of meat, dairy, and seafood.

“Curiously, when a saturated fat-rich diet was supplemented with fish oil, the mice did not suffer from sepsis,” added Gibson (ISSFAL 2014).

As she said, “These intriguing findings suggest that omega-3 supplementation with a diet high in saturated fat may be more protective to the GI tract than a diet rich in omega-6 fats.” (ISSFAL 2014)

We should note that, some of the rodents fed diets high in omega-3s suffered fatal sepsis … whole body inflammation due to severe infection.

These deaths resulted from the extreme, artificial situation the scientists created to reveal the effects of omega-3 and omega-6 fats on the overall microbiome and resistance to colitis and related disorders.

As lead author Deanna Gibson, Ph.D., said, “While too much inflammation isn't good in the context of autoimmune disease, we also need inflammation to survive against infections.” (ISSFAL 2014)

“These observations suggest that excess omega-6 intakes may be harmful to gut health. Conversely, while omega-3 supplementation promotes beneficial microbes in the gut, thereby decreasing inflammation, this advantage under normal conditions may be problematic in the presence of harmful bacteria.” (ISSFAL 2014)

It's important to stress that people eating diets high in omega-3s have never been found to be at greater risk of infection or sepsis.

In fact, the opposite is true ... several studies published this year suggest that omega-3s help control sepsis (Mo Y et al. 2014; Hall TC et al. 2014; Russel D et al. 2014; Chen J et al. 2014; Tustumi R et al. 2014; Gultekinn G et al. 2014).

And deficiencies of the omega-6 fats needed to help control inflammation in sepsis are virtually unknown … in fact, the average American's diet has far too many omega-6s (mostly from cheap vegetable oils) and too few omega-3s … see “America's Sickening Omega Imbalance”, “Know Your Omega-3/6 Numbers”, and the Omega-3 / Omega-6 Balance section of our news archive.

What's the take-away?
These were animal studies, so we can't be sure that the results apply to people ... but, based on the available human research, it seems likely that they do (again, see “The Culture War in Your Gut”).

If so, the average American diet – too low in omega-3s and too high in omega-6s – probably predisposes people to metabolic and intestinal trouble.

So it seems wise to do two things.

Avoid the cheap vegetable oils high in omega-6s fats (corn, soy, safflower, and sunflower) in favor of olive, canola, coconut, and macadamia nut oils ... and avoid the packaged and prepared foods made with vegetable oils high in omega-6s.

And be sure to get plenty of omega-3s ... especially DHA and EPA from seafood and fish oils.

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