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Big Gut-Health Boost from Fish and Plant Foods
Yogurt and supplements grab the spotlight but aren’t the only stars

02/11/2019 By Craig Weatherby

It’s time for a gut-check … but this isn’t about yogurt or pickled veggies.

Fast-growing evidence shows that gut health is truly key to a healthy body and mind.

People are powerfully drawn — or lured — to “probiotic” pills and cultured foods such as yogurt or fermented veggies, which provide friendly bugs.

But much remains unknown about the effects of specific probiotic bugs in specific people, and that's prompted a renewed focus on “prebiotic” foods and supplements.

Prebiotics appear more reliably and broadly valuable, because they fuel the growth of many beneficial bacteria — and generally don’t fuel unfriendly bugs.

Most of the prebiotics in many Americans’ diets are plant fibers like inulin or FOS from vegetables, beans, and grains, which are also available as dietary supplements

Now, exciting evidence suggests that plant-source antioxidants and seafood-source omega-3s also provide major prebiotic boosts to friendly gut bacteria.

Before we scan some recent findings, let’s quickly review the roles that gut bacteria play in human health.

The role your GI biome plays in good health
More than 100 trillion bacteria and other microbes dwell in your gut — some good, some bad.

Together, these microbes constitute what’s called the microbiome or microbiota, which encompasses about 1,000 unique microbial species.

The two terms get used interchangeably, but “microbiota” originally meant the microbes in your gut, skin, or other organ, while “microbiome” meant an entire microbial environment, such as in a person’s stomach: its microbes, their genes, free-floating gene fragments, and more.

Your gut biome helps extract energy from foods, produce micronutrients, battle unfriendly bacteria, and help keep your immune system on an even keel.

Conversely, an unbalanced biome can promote everything from obesity, diabetes, and allergies, to irritable bowel syndrome (IBS), colitis, and inflammatory bowel disease (IBD).

Myriad factors influence each person’s unique microbial mix — especially your diet, age, environment, and genetic profile.

We know that certain things can throw your gut bacteria badly out of balance:

  • Antibiotics
  • Excess dietary sugar and starch
  • Diets low in "probiotics" such as the friendly bugs in fermented foods.
  • Diets low in "prebiotics" such as fiber, and the "resistant" starch in beans, which feed and foster the growth of friendly bacteria.

And recent findings suggest that this list of negative factors should include “diets low in antioxidant-rich whole plant foods and seafood-source omega-3 fatty acids”.

Unfortunately, many Americans don't eat nearly enough seafood or whole plant foods.

“Prebiotic” antioxidants and beneficial gut bugs: A mutual aid society
Biochemists have begun to reveal the relationship between foodborne antioxidants and beneficial gut bacteria: a bond that’s very likely to boost human health.

The antioxidants in plant foods fall into two general categories: carotenoids and polyphenols.

  • Carotenoids are red-orange-yellow compounds that lend their color to whole plant foods like carrots, peppers, and wild salmon.
  • Polyphenols are compounds from berries, grapes, and other fruits, vegetables, beans, nuts, whole grains, tea, coffee, raw cocoa, dark chocolate, and other whole plant foods.

Three years ago, scientists from the University of Massachusetts, China, and Turkey collaborated on a review of the evidence concerning interactions between foodborne polyphenol-type antioxidants and gut microbes (Ozdal T et al. 2016).

As they wrote, “Two-way, reciprocal interactions of gut microbiota and phenolic compounds [polyphenols] have an important impact on the bioavailability of phenolic compounds and human health.”

Here’s how the international team described the relationship between polyphenols and gut bacteria: “Phenolic compounds that are not readily absorbed in the small intestine serve as growth substrates [growth mediums] for members of the gut microbial community, which in turn modify the bioavailability and nutritional properties of these compounds.”

In other words, dietary polyphenols promote the growth of beneficial gut bacteria, which in turn enable polyphenols’ antioxidant, anti-inflammatory, and other healthful effects.

Why should we care about absorption of polyphenols from fruits, vegetables whole grains, nuts, seeds, and other whole, unprocessed plant foods?

The U.S.-China-Turkey team noted the substantial evidence that polyphenols can help prevent or diminish arteriosclerosis (hardening of the arteries), ulcers, cancer, damaging inflammation, and dangerous blood clots.

To be absorbed, polyphenols must first be freed from fibers or other structures within plant foods. Our own digestive enzymes do much of that work, making them available for absorption — assuming they’re small enough and occur in an absorbable form.

But many polyphenols are very large molecules, which is why only 5% to 10% of them get absorbed in the small intestine — a low rate compared with other micronutrients.

So, before they can exert any healthful effects, most dietary polyphenols must be metabolized by gut bacteria — a process that transforms them into smaller, more absorbable and “bioactive” molecules.

Note: Although carotenoids and polyphenols are commonly called “antioxidants”, they exert most of their beneficial effects indirectly, via their influence on our so-called “working” genes — including stimulation of the body’s own antioxidant network. For more on that topic, see Food-Borne Antioxidants May Act Indirectly.

UK study shows gut benefits from omega-3s
Two years ago, British researchers published the intriguing results of a clinical study in pairs of female twins.

They wanted to compare the women’s blood levels of omega-3 fatty acids — and estimated intakes of omega-3s — to the diversity and health of their gut microbiota (Menni C et al. 2017).

The UK group analyzed data collected from 876 middle-aged and elderly female twins (average age 65) who’d previously been studied to look for links between their genetic profiles and gut microbiomes as they relate to weight gain and disease.

And the results of the new analysis linked higher blood levels of omega-3s — especially DHA — and higher dietary intakes of omega-3s to healthier, more diverse microbiomes.

The healthier microbiomes seen in the women with higher omega-3 blood levels and dietary intakes were in part signaled by higher levels of a friendly bacteria called Lachnospiraceaes.

Although previous research suggested that omega-3s might benefit the microbiome, this is the biggest human study on the subject — which makes the results more meaningful than findings from animal studies or small human studies.

The authors acknowledged that it’s impossible to be completely certain whether the women’s omega-3 intakes improved their microbiome diversity/health or vice versa.

However, the analysis linked the women’s estimated omega-3 intakes to the diversity/health of their microbiomes — a link almost as strong as to omega-3 blood levels.

That finding suggests that the higher blood levels of omega-3s seen in women with healthier microbiomes was more likely the cause of better gut health, rather than its effect.

As the researchers wrote, the somewhat weaker link between estimated omega-3 intakes and microbiome health, “… is likely to simply reflect the [relative unreliability] of accurate estimates of [omega-3] intake from food questionnaire data, compared to the accuracy of serum [blood] level measurements.”

Finally, the British team linked high omega-3 blood levels to high fecal levels of NCG (N-carbamylglutamate) — a compound that exerts antioxidant effects in the gut, and is likely to reduce inflammation.

According to co-author Dr. Cristina Menni, “We believe that some of the good effects of omega-3 in the gut may be due to the fact that omega-3 induces bacteria to produce this substance.”

Earlier studies shed additional light on omega-3s and the gut
Two animal studies published in 2014 examined the effects of dietary omega-3 and omega-6 fatty acids impact gut health.

It’s been shown that the relative intakes and blood levels of these two families of fatty acids can affect the risks and severity of inflammatory bowel disease, colitis, and Crohn’s disease.

Study #1
A University of British Columbia team led by Dr. Deanna Gibson, Ph.D., examined how omega-3 and omega-6 fatty acids affected mice whose guts were deliberately infected with a microbe known to promote colitis.

The mice with diets high in omega-6 (from corn oil) experienced more intestinal damage, immune-cell damage, and growth of harmful bacteria.

In contrast, the mice fed diets high in seafood-source omega-3 EPA and DHA had higher levels of anti-inflammatory microbes known to reduce the damage caused by colitis.

However, mice on the omega-3-rich diet suffered sepsis, because their immune responses to the artificially introduced colitis-causing bacteria were impaired.

As Dr. Gibson said, “… 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 [excessive amounts of] harmful bacteria.”

Interestingly, when mice were fed a diet rich in saturated fats plus fish oil, they did not suffer from sepsis from the artificially introduced pathogen.

This finding supports the idea that diets dominated by saturated fats and omega-3s are generally healthier than diets — such as the standard American diet — that feature an overload of omega-6 fats.

Study #2
This mouse study came from scientists at Harvard Medical School and Massachusetts General Hospital.

They found that diets providing a lower ratio of omega-6 to omega-3s lowered the amounts of harmful bacteria while boosting the amounts of beneficial bacteria, and thereby improved the animals' gut biomes.

This healthy balance in the animals’ gut biomes also led to lower levels of inflammation.

Lead researcher Jing X. Kang, M.D., Ph.D., said this about their findings:

  • “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 PUFA ratio to optimize gut microbiota — such as reducing intake of vegetable oils high in omega-6 fat, processed foods and grain-raised livestock and increasing intake of fish and green vegetables — could prove effective for managing such diseases.”
  • “For management of certain health conditions, a high quality, concentrated omega-3 supplement is also practical.”

So, to maximize your gut health, it makes sense to ensure you’re getting plenty of fish — or fish oil — as well as ample amounts of fiber and fermented dairy foods or vegetables.


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