Natures wonders: human gut microbiome controls health (Introduction)

by David Turell , Monday, November 19, 2018, 21:47 (2194 days ago) @ David Turell

Studies of Western and African diets establishes the importance of types of bacteria we carry and how they affect our health. This is a very long article which I can only skim:

http://nautil.us//issue/30/identity/how-the-western-diet-has-derailed-our-evolution?utm...

"A group of Italian microbiologists had compared the intestinal microbes of young villagers in Burkina Faso with those of children in Florence, Italy. The villagers, who subsisted on a diet of mostly millet and sorghum, harbored far more microbial diversity than the Florentines, who ate a variant of the refined, Western diet. Where the Florentine microbial community was adapted to protein, fats, and simple sugars, the Burkina Faso microbiome was oriented toward degrading the complex plant carbohydrates we call fiber.

"Scientists suspect our intestinal community of microbes, the human microbiota, calibrates our immune and metabolic function, and that its corruption or depletion can increase the risk of chronic diseases, ranging from asthma to obesity.

“'It was the most different human microbiota composition we’d ever seen,” Sonnenburg told me. To his mind it carried a profound message: The Western microbiome, the community of microbes scientists thought of as “normal” and “healthy,” the one they used as a baseline against which to compare “diseased” microbiomes, might be considerably different than the community that prevailed during most of human evolution.

"And so Sonnenburg wondered: If the Burkina Faso microbiome represented a kind of ancestral state for humans—the Neolithic in particular, or subsistence farming—and if the transition between that state and modern Florence represented a voyage from an agriculturalist’s existence to 21st-century urban living, then where along the way had the Florentines lost all those microbes?

"Humans can’t digest soluble fiber, so we enlist microbes to dismantle it for us, sopping up their metabolites. The Burkina Faso microbiota produced about twice as much of these fermentation by-products, called short-chain fatty acids, as the Florentine. That gave a strong indication that fiber, the raw material solely fermented by microbes, was somehow boosting microbial diversity in the Africans.

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"But what the Sonnenburgs’ experiment suggests is that by failing to adequately nourish key microbes, the Western diet may also be starving them out of existence. They call this idea “starving the microbial self.” They suspect that these diet-driven extinctions may have fueled, at least in part, the recent rise of non-communicable diseases. The question they and many others are now asking is this: How did the microbiome of our ancestors look before it was altered by sanitation, antibiotics, and junk food? How did that primeval collection of human microbes work? And was it somehow healthier than the one we harbor today?

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"Most study subjects live in the tropics; their microbial communities may reflect tropical environments, not an ancestral human state. Yet even “extinct” microbiomes from higher latitudes—including from a frozen European mummy—are similarly configured to break down plant fiber, adding to the sense that the Western microbiome has diverged from what likely prevailed during human evolution.

"The Sonnenburgs think fiber is so important that they’ve given it a new designation: microbiota-accessible carbohydrates, or MACs. They think that the mismatch between the Westernized, MAC-starved microbiome and the human genome may predispose to Western diseases.

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"Soluble fiber is an umbrella term for complex plant sugars—including some polysaccharides, oligosaccharides, and fructans. The molecules consist of simple sugars linked together in long, hard-to-dismantle chains. If you dump a load of fiber—or microbiota-accessible carbohydrates—onto a colonic community of microbes, those that specialize in fermenting it will bloom. And they’ll start churning out short-chain fatty acids, including butyrate,

"These acids, Sonnenburg thinks, are one of the long-sought mechanisms by which fiber prevents disease. Rodent studies suggest that as they diffuse into circulation, they stimulate the anti-inflammatory arm of the immune system—cells that help you not attack tree pollen and other harmless proteins—preventing allergies and other inflammatory diseases. The calming effect reaches as far as the bone marrow and lungs,

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"In their recent book, The Good Gut: Taking Control of Your Weight, Your Mood, and Your Long-term Health, the Sonnenburgs argue forcefully that boosting fiber intake is the best way to cultivate a healthier community of microbes. Given the many unknowns, their advocacy surprised me. The science wasn’t settled; what if they were wrong?

"They’d fretted over this scientific uncertainty, they said, but decided that the diet they pushed—really a variant of the Mediterranean diet—would probably not cause harm, and would likely benefit adherents, even if everything they thought about the microbiome was wrong."

Comment: We need fiber and we need the gut bacteria to digest it. Bacteria make up a significant amount of body weight, and what this shows is that the persistence of bacteria since the origin of life is because of this necessary relationship. Multicellular organisms can't do everything they need by themselves.