Call for caution on the microbiome: guess what, there is no such thing as an "ideal" microbiome. Studies of healthy people show surprisingly little commonality in their gut bacteria.

Microbiomes are as diverse as people:

The microbiome is the sum of our experiences throughout our lives: the genes we inherited, the drugs we took, the food we ate, the hands we shook. It is unlikely to yield one-size-fits-all solutions to modern maladies.

We cling to the desire for simple panaceas that will bestow good health with minimal effort. But biology is rarely that charitable. So we need to learn how tweaking our diets, lifestyles and environments can nudge and shape the ecosystems in our bodies. And we need ways of regularly monitoring a person’s microbiome to understand how its members flicker over time, and whether certain communities are more steadfast than others.

Our microbes are truly part of us, and just as we are vast in our variety, so, too, are they. We must embrace this complexity if we hope to benefit from it.

wow.  like little universes within us... each one unique.

well, that's kind of a relief!  there is no ideal to be seeking.  we just need to do what feels good for ourselves, individually.

It explains why different diets work for different people.

And why different people have different moods / personalities / decision making techniques.

And it means we really need to learn who we are so we can be our best self!

We are each a universe unto ourselves.

yes.

and we need to be aware of what really makes us feel good—for real, not just for now.

It's challenging to figure out what really makes us feel good. Must experiment every day!

now THAT is a good daily experiment!

Do you do daily experiments to try to figure out what makes you feel good?

Rather than unhealthy or healthy microbiome we need to embrace the notion that microbiomes are complex, diverse ecosystems.

These microscopic partners help us by digesting our food, training our immune systems and crowding out other harmful microbes that could cause disease. In return, everything from the food we eat to the medicines we take can shape our microbial communities — with important implications for our health. Studies have found that changes in our microbiome accompany medical problems fromobesity to diabetes to colon cancer.

As these correlations have unfurled, so has the hope that we might fix these ailments by shunting our bugs toward healthier states. The gigantic probiotics industry certainly wants you to think that, although there is little evidence that swallowing a few billion yogurt-borne bacteria has more than a small impact on the trillions in our guts. The booming genre of microbiome diet books — self-help manuals for the bacterial self — peddles a similar line, even though our knowledge of microbe-manipulating menus is still in its infancy.

This quest for a healthy microbiome has led some people to take measures that are far more extreme than simply spooning up yogurt. In September, the archaeology writer Jeff Leach used a turkey baster to infuse his guts with the feces of a Hadza tribesman from Tanzania. Doctors have carried out hundreds of fecal transplants, particularly to treat people with unshakable infections of the diarrhea-causing bacterium Clostridium difficile. The procedure has been spectacularly successful, far more than conventional antibiotics.

But Mr. Leach did not have C. difficile. He experimented on himself because he views the Western microbiome as “a hot microbial mess,” he wrote on his blog. Poor diets, antibiotics and overly sanitized environments have gentrified the Western gut, he wrote, “potentially dragging us closer to ill health.” The Hadza, with their traditional hunter-gatherer lifestyle, carry diverse microbial communities that are presumably closer to a healthier and disappearing ideal. Hence the stunt with the turkey baster. Mr. Leach billed it as “(re)becoming human.”

This reasoning is faulty. It romanticizes our relationships with our microbes, painting them as happy partnerships that were better off in the good old days. It also invokes an increasingly common trope: that there is a “normal” or “healthy” microbiome that one should aim for. There is not. The microbiome is complex, varied, ever changing and context-dependent — qualities that are the enemies of easy categorization.