I Contain Multitudes: The Microbes Within Us and a Grander View of Life, by Ed Yong

As stated in The Germ Files, by Jason Tetro, your human cells (about 37 trillion in a typical person) are outnumbered by the 100 trillion or so microbes living in and on us.  According to Ed Yong, the best guess now is that there are around 30 trillion human cells and 39 trillion microbial cells in every person.  Either way, the bacteria, viruses, and fungi that we host are mostly harmless, but some are helpful and a few are harmful.

In I Contain Multitudes, Yong presents the view that the human body is an ecosystem, not a single, individual entity.  In fact, he questions the very nature of individual identity – microbes share the same space as our bodies, influence the development of some animals, and, like an organ, can contribute to the good of an animal, for example by providing essential nutrients to their hosts.  Microbial genes can even enter the cells of their hosts, becoming part of their genome.  Perhaps we should view our microbes as part of us instead of just living in and on us.

Like a macroscopic ecosystem, a microbiome can be thrown out of balance by things like disease or poor diet.  Microbes are not always helpful nor always harmful; it depends on the context.  A bacteria that helps extract nutrients from the digestive tract is helpful, but if it enters the bloodstream it can be harmful.  Like a garden, where a weed is a plant out of place, we can use the metaphor of farming to change our thinking about germs.  Instead of attacking and eradicating them, we can cultivate, feed, and weed them.

There are weird stories from the animal and insect worlds, where some microbes have a strong influence on their hosts.  Microbes influence the sex lives of insects, stimulate development of the bio-luminescent organs of squid, and provide nutrients without which the host could not survive.  One insect has bacteria living inside its bacteria, and all three – the host plus two bacteria – contribute to nutrient production.  Others neutralize toxins using genes obtained from bacteria.  Yong shows how this all makes sense in the context of evolution.

Our new understanding of the role of microbes is proving beneficial.  Dosing frogs with bacteria can protect them against a deadly fungus; giving Australian livestock new gut bacteria allows them to digest new, drought-tolerant plants; cultivating bacteria in mosquitoes prevents them from spreading dengue fever.

For Tetro, probiotics are the way to keep your microbiome in balance, but Ed Yong presents a more cautious view.  Most commercially available probiotics contain too few microbes to make a difference, and contain types of microbes that are not important to the human gut and which do not persist there for very long.  The concept of probiotics is sound, but the hype exceeds the reality.  One approach that does work is a fecal transplant to treat c. difficile, an antibiotic resistant infection.  Perhaps we can find out which bacteria in the donor poop are doing the job, and customize a treatment that doesn’t involve having someone else’s feces introduced into our guts.

The Germ Files: The Surprising Ways Microbes can Improve Your Health and Life (and How to Protect Yourself from the Bad Ones), by Jason Tetro

Well, the title and (rather lengthy) sub-title say it all.  Many will know by now that human cells (about 37 trillion in a typical person) are outnumbered by the 100 trillion or so microbes living in and on us.  The bacteria, viruses, and fungi that we host are mostly harmless, but some are helpful, and a few are harmful.  The trick is to keep the different types in balance, so the friendly microbes don’t turn on us, and the harmful ones don’t flare up and cause illness.  Tetro tells us the key to good health is microbial diversity, which in turn is promoted by a healthful diet rich in raw fruits and vegetables, and by probiotics, whether from naturally fermented foods or from supplements.

Each chapter is composed of a series of short articles related to the chapter topic; which include, among others, hygiene, antibiotics and probiotics, health, food, and sex.  All these things have an impact on the microbes we host, and the microbes have an impact on us.  The explanations of the digestive and immune systems are clear, and the roles of microbes (mostly bacteria) in influencing these systems are described in many contexts.  There are helpful hints, like putting your stinky boots outside in the cold in winter to freeze the bacteria and freshen them up, or to eat unpasteurized sauerkraut to ingest helpful bacteria.  There are tips on keeping pets, tanning safely, and tattoos and piercings; answers to the questions of whether chocolate is really good for you and if we all should avoid gluten; and lots of information about how microbes can trigger inflammation in the body and how to avoid it.

As always, the main path to good health is through a sensible diet and exercise.  For Tetro, it also includes probiotics.