Probiotics are beloved by many health-conscious folks.

They fit that sweet spot between natural (always good, right?)

and medical (must have health benefits).

I get legit hate mail if I write anything less-than-glowing about probiotics.

But the truth is, probiotics arent automatically always good.

A few weeks ago we had a hint ofone reason to be suspicious.

Most are bacteria, but yeasts and other microbes could possibly fit the description.

Our bodies need bacteria and other microbes.

The bacteria on our skin prevent other, nastier germs from moving in and causing trouble.

Research into our relationship with these microbes has exploded in recent years.

They produce chemicals that our bodies need, and vice versa.

We know that a healthy microbial ecosystem is essential to a healthy body.

Probiotic Is Too Vague a Term

Browsing through theCochrane reviews on probiotics, a theme emerges.

Its probably not fair to treat probiotics as if it were a single, known entity.

Remember our rainforest analogy for the gut microbial ecosystem.

Now ask if animals could help a rainforest thrive.

Depending on which animals, and how many, and when and how you released them.

For example, probioticscan prevent a deadly infection called NECin premature babies.

Formulations are chosen, instead, based on whats readily available.

And manufacturers are not always doing enough testing to see what ends up in the pills.

In 2014, a premature baby died, at eight days old, of a rare fungal infection.

We dont know how often probiotics might be contaminated like this.

Probiotics can also be antibiotic-resistant.

Thats not necessarily a bad thing, especially if youre taking them to reduce the side effects of antibiotics.

Typically, probiotic bacteria dont take up residence in our gut.

But the relationship is probably more complex than that.

Much of the research thats been done on the gut microbiome relies on these not-necessarily-reliable stool samples.

Now, two recent papers in the journalCellthrow a wrench into the works.

Both found that probiotics interact with our native microbes in complex and possibly harmful ways.

Its not too far a leap from those results to suggest that probiotics should be personalized.

But the researchers behind the studies also run apersonalized nutrition service, so Im a little bit skeptical.

Bacteria are a normal component of yogurt, after all.

But a dose of beneficial microbes can also be a drug.

In this case, the FDA considers the bacteria to be a drug.

But all of that is unknown for now.

CFUs, or colony-forming units, roughly measure how many live microorganisms are in the product.

(Just like dog breeds, bacteria can come in different varieties while still being the same species.)

But all the other unknowns remain.

Does a probiotic product contain exactly whats on the label, and no more?

Has it even been tested on people like me?

But you wouldnt know any of that from probiotic companies marketing.

Meanwhile, probiotics are a favorite of nutritionists, chiropractors, and other expertslegit ones and quacks alike.

Theres also the huge problem that if one probiotic works for one condition, that doesnt meanallprobiotics work foranycondition.

There are hundreds of probiotics, and surely they all arent good for everything.

We have a hard enough time, as a society, understandingvitaminsfor chrissakes.

We know what doses will prevent and treat diseases.

And yet, people still cant keep straight when and whether you need them.

Thats not good logicmost people arent magnesium deficientbut it sells.

Probiotics have the same cachet as vitamins, with a more nebulous scientific backing.

Surely some are safe, and some are effective, but which are they?

It will be a while before science has any definitive answers.