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What are Probiotics? What's Wrong With Them?

Here's the problem with probiotics: Part 1


Probiotics – they are large, they contain multitudes. 

Probiotics are big money – $40 billion per year (and growing). Just look at the supermarket shelf. Nestlé, Unilever, and General Mills have been betting big on probiotics for a while now.

But what are they betting on? But depending on where you sit, a probiotic can be any number of things: A healthy ingredient with a loose affiliation to yogurt. A new-product buzzword on your latest fermented beverage. A daily pill to go with your vitamins. Or, if you have a condition like Chron’s or ulcerative colitis, one of the only reliefs you have.

Which raises a few questions. 

  • What qualifies as a probiotic anyway? (way more than you think)
  • What are probiotics supposed to do? (not much specific)
  • And do they do it? (not really)

In Part 1 of this post, we look at the first of these questions: what is a probiotic, really?

In Part 2, we dive into the second two, and ask what they mean for the future of probiotic products.

Part 1

What are Probiotics?

The first thing to know, is that the term “probiotic” itself is a catch-all. The official definition comes from a conference of scientists who met in 2001 in Cordoba, Argentina. They were there as part of a United Nations summit convened to help Argentina settle a trade dispute related to powdered milk. In that rarified context, this group of experts arrived at a definition of probiotics that has held sway over the industry ever since:

"Live microorganisms which, when administered in adequate amounts, confer a health benefit on the host.” UN Report

That, and that largely alone, is the definition of probiotics that holds sway worldwide. It is very broad. And problematically, its that breadth that hides a lot of questionable industry behavior from the eyes of consumers. 

So let’s try to understand it by breaking it down…

The first thing to notice is that even though we usually talk about gut probiotics you eat, there’s nothing gut-specific about them. Probiotics are used in skincare, mouthwash, foot cream, all sorts of things. Here, we’ll talk about gut probiotics – which are the most familiar – but know that they’re far broader than that. Now let's get to the definition.


These things are alive, which matters more than you might think. To have an effect, gut probiotics need to be alive in the gut, which means they need to be resilient enough to survive passing through the stomach and reaching the intestines. Stomach acid is harsh and can be quite deadly to microbes. This brings us to potential bad behavior #1 among probiotics manufacturers…

Some things labeled as probiotics actually may not survive the stomach acid. They might never get the gut! If a probiotic label says in vitro, all that means is that it has had an effect in a test tube. It does not mean that it will work in vivo, in the body, when it has to survive the stomach acid. Probiotic labels often play on this confusion. See if you can spot the “in vitro” in this probiotic's packaging:

ProViotic organic vegan probiotic

Source: Twitter @ProViotic_UK


Probiotics can be yeasts and other microbes, but the vast majority of commercial probiotics are good bacteria, identified by name in 2 parts: the species and the strain.

Part 1 is the species. An example is “Lactocaucus lactis.” That’s a mouthful, so all of it gets abbreviated as “L. lactis,” which follows the naming convention of the first letter of the genus abbreviated, then the species name.

Part 2 of identifying a probiotic is understanding that within a species, there are many different strains. A strain is a particular genetic variant of the species. Strain names are usually combinations of letters and numbers, like “O26.” The important thing to recognize is that within a species, each strain can be very different.

Let’s take, for example, the species E. coli. We hear a lot about E. coli outbreaks of foodborne illnesses. But some strains of E. coli are actually considered probiotics. Within the E. coli species, different strains show massive variation. One study analyzing E. coli DNA found that 80% of E. coli genes could vary from strain to strain! That means only 20% of all E. coli genes were considered core to the species. That’s how E. coli O26 could cause an infectious outbreak at Chipotle in 2016, while E. coli DSM 17252 can be sold as a probiotic.

This brings us to the potential bad behavior #2 of probiotics marketers: intentionally confusing species and strain. If you look online, you’ll see countless probiotics companies hawking what look like the same probiotics, but what really are only the same species, not the same strains. And as we saw, that means they can have very different effects.

Probiotic strain example showing two L. acidophilus products with species but not strain number

Are these 2 L. Acidophilus products the same? Impossible to know.

This creates a ton of confusion and hides all sorts of bad behavior by less-than-ethical companies.*

*We care a lot about this. So much so that our CEO/co-founder Zack Abbott recently testified in his capacity as a PhD Microbiologist and small business owner before the California State Assembly in support of Assembly Bill No. AB-1178 – a new California law that would require both species and strain be identified on probiotic labels.

Zack Abbott testifying supporting AB-1178

Zack during his testimony on April 2, 2019.

“which when administered in adequate amounts”

Whatever probiotics are supposed to do, it often depends on having enough of them there to do it. Probiotics are quantified in Colony-Forming Units (“CFUs”). Because probiotics are often intended to crowd out other microbes, it may take billions of CFUs to hit that crowd-out threshold and see a desired effect.

But here’s where we see potential bad behavior #3. More does not necessarily mean better. Probiotics makers often ignore this fact or fail to mention it in advertising, but taking too many probiotics can perturb the microbiome. This can lead to health problems and a condition known as dysbiosis.

“confer a health benefit”

What are probiotics supposed to be doing anyway? There are generally 3 ways probiotics are supposed to work:

  1. Crowd out bad microbes
  2. Help the body do something better
  3. Do something the body cannot do on its own

And here we have potential bad behavior #4. Manufacturers are not very clear about what the effect of a probiotic is supposed to be. Furthermore, there is often very little data to substantiate even general effects. To this day, no clinically tested probiotic has ever been approved by the U.S. Food and Drug Administration (FDA). Probiotics on the market now are compliant for safety, but none have been proven efficacious. This behavior is the most significant, and we’ll dive deeper into this shortly.

“on the host”

One final fact of interest: probiotics are not just for humans. Some of the largest probiotics buyers are in the veterinary and agricultural industries, where probiotics are often fed to animals.

So, there it is! Probiotics defined. Feel satisfied? Neither do we. There is a huge amount of variability here. And with it, much room for confusion. But it’s not yet time to throw the baby out with the bathwater. 

In Part 2, we dive deeper into what good probiotics are supposed to be doing, and, more importantly, whether they are actually doing it. Check out Part 2 now.