Probiotics 101: What They Are and How They Actually Work
You see the word probiotics everywhere: in yogurt, capsules, gummies, drinks, teas, and on all kinds of food labels. But when someone says, "Hey, you should take a probiotic," figuring out your next step is extremely confusing. How many CFUs do you need? What even is a CFU? What about AFUs? This one has spores, this one has 5 strains, this one has 30. Personally, as a nutrition coach and trainer, I never recommended a probiotic in the past, simply because I wasn't sure about the ones I had taken myself.
This post keeps it simple, and we'll start with what matters most: how to read a probiotic label. If you read at least that far, you'll know exactly what to look for the next time you're shopping for a probiotic, in the store or online. After that, we'll cover what probiotics are, how they actually work, and where the idea came from.
No hype. Just the basics.
How to Read a Probiotic Label
Let's answer those label questions first. Here's what to look for:
- A delivery system. Your stomach is full of strong acid, and without protection, it can kill a lot of the bacteria before they ever get a chance to do their work. Look for a delivery system designed to get them past your stomach and into your intestines, where they do their job. If a product doesn't mention one, you may be watching your hard-earned money go down the drain.
- Prebiotics. Prebiotics are the fuel and food for your good bacteria, so seeing them on the label is a good sign. A product that pairs probiotics with prebiotics is called a synbiotic.
- Activity. This is the count of live bacteria, measured in billions. Most labels use CFU (colony forming units), which counts bacteria by growing them on a lab plate. Some, like NSTINCT, use AFU (active fluorescent units), which counts live cells directly using a laser-based test called flow cytometry. AFU also catches live bacteria that won't grow on a plate, so AFU and CFU numbers aren't a one-to-one comparison (BMC Microbiology, 2023). You want enough to see the benefits, but a bigger number doesn't automatically mean a better product. For most companies the total number is based on the research behind strains included.
- Strains. Ideally, you'll see a broad spectrum of different strains, each listed with its strain number (the letters and numbers after the name). Some labels also show the activity count for each strain. Not all strains are created equal, and brands that care will choose strains the best ones for you.
- Postbiotics. If you see these on a label, the company took things one step further for you. Postbiotics are beneficial compounds and parts left behind by good microbes, and they can help support a healthy environment for your good bacteria to do their job (Salminen et al., 2021).
What Are Probiotics?
"Live microorganisms which when administered in adequate amounts confer a health benefit on the host." Basically, probiotics are good bacteria (plus a few helpful yeasts). When you take enough of them, they help your body. That's the official definition used by scientists around the world (Hill et al., 2014).
Your gut is already full of bacteria, roughly 38 trillion of them by one widely cited estimate (Sender et al., 2016). Most of them live in your large intestine. Some help you and some don't. Probiotic supplements add more of the helpful kind.
There are lots of different types. The most common ones you'll see on labels are Lactobacillus, Bifidobacterium, Streptococcus thermophilus (the one used to make yogurt, not the one behind strep throat), and Saccharomyces boulardii (more on that one below). You don't need to memorize them. Just know that a mix of different good microbes is a good thing.
Not Every Probiotic Is a Bacteria
Most probiotics are bacteria, but one of the most studied is actually a yeast: Saccharomyces boulardii. It was first discovered in the 1920s on the skins of lychee and mangosteen fruit. Because it's a yeast, antibiotics don't kill it the way they kill bacteria. That's why people often take it during or after a round of antibiotics to help support a healthy gut balance (NIH Office of Dietary Supplements). It's also one of the probiotics in the NSTINCT Broad Spectrum Probiotic.
How Probiotics Work
Probiotics don't work like a medicine aimed at one thing. Think of them more like adding good workers to a busy job site. They have three main jobs:
- Crowding out the bad guys. Good bacteria take up space and eat the food that harmful bacteria would otherwise use. Less room and less food make it harder for the bad guys to take over.
- Making helpful compounds. As good bacteria break down food, they make useful things like short-chain fatty acids, which help feed the cells lining your gut. Scientists call these helpful byproducts metabolites.
- Working with your immune system. A big part of your immune system sits right along your gut lining, and good bacteria help support how it works.
These benefits are well recognized across many different probiotics (Hill et al., 2014).
One more thing most people don't know: most probiotics don't move in for good. Many pass through your system over days or weeks, doing their jobs along the way. That's why taking them consistently is a good idea.
A Quick Timeline
- 1822: Army surgeon William Beaumont studied a fur trapper's stomach through an unhealed gunshot wound and proved digestion runs on strong stomach acid. Some of that work happened right here in Wisconsin (Britannica).
- 1899: French pediatrician Henry Tissier discovered Bifidobacterium in the guts of breastfed babies (ISAPP, 2019).
- Early 1900s: Nobel Prize winner Élie Metchnikoff linked fermented milk to long, healthy lives and proposed that good bacteria could crowd out bad ones.
- 1965: The word "probiotic," meaning "for life," was first used.
- 2007: The National Institutes of Health launched the Human Microbiome Project to map the bacteria living in and on the human body (NIH Human Microbiome Project).
Meet the "Biotics" Family
You'll see a few similar words on labels. Here's the simple version:
- Probiotics are the live good bacteria (and yeasts) themselves.
- Prebiotics are their food: special fibers your body can't digest, but your good bacteria can (Gibson et al., 2017).
- Postbiotics are good microbes that are no longer alive, along with their parts and the compounds they made, that still benefit your health (Salminen et al., 2021).
- Synbiotics combine probiotics and prebiotics in one product.
We'll dig into prebiotics and how they compare to probiotics in one of our next post.
Probiotic Foods vs. Supplements
You can get probiotics from food. Some good probiotic foods are:
- Yogurt and kefir that say "live and active cultures" on the label
- Sauerkraut and kimchi from the cold section of the store
- Miso and tempeh
- Kombucha
One thing to know: heat kills these bacteria. So if a food is cooked, baked, or canned, the good bacteria are usually gone.
Food is a great place to start. The problem is that you never really know how much good bacteria you're getting, or which kinds. A probiotic supplement gives you the same amount of the same bacteria every day.
Common Probiotic Myths
"All bacteria are bad." Most of the bacteria in your gut are harmless or helpful. You couldn't digest your food well without them.
"More is always better." A bigger number doesn't automatically mean a better product. The right types, a guaranteed count, and good delivery matter just as much, if not more.
"Yogurt is all you need." Yogurt is a great food, but the amount and types of live bacteria vary a lot. Some yogurts are even heat-treated after they're made, which kills the live cultures.
Who Should Check With a Doctor First
Probiotics are safe for most healthy people, but not for everyone. If you have a weak immune system, a serious illness, or you're pregnant, talk to your doctor before you start one.
Where NSTINCT Fits
We made the NSTINCT Broad Spectrum Probiotic with all of this in mind. It has 30 probiotic strains, including Saccharomyces boulardii, and 40 billion AFU in every serving. It includes three prebiotic fibers, so the bacteria come packed with their own food, plus our MAKTabolite® postbiotic, all protected by our MAKTrek® delivery system. That's more than 40 intentional ingredients and zero fillers. Every milligram we could fit in the capsule is there for a reason.
A probiotic isn't magic. It works best alongside a healthy diet with plenty of fiber. But if you want an easy, steady way to support your gut every day, that's what a probiotic is for.
Ready to start? Learn more about the Broad Spectrum Probiotic at nstinct.com.
References
- Hill C, Guarner F, Reid G, et al. Expert consensus document: The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nature Reviews Gastroenterology & Hepatology. 2014;11(8):506-514. PubMed
- Sender R, Fuchs S, Milo R. Revised estimates for the number of human and bacteria cells in the body. PLOS Biology. 2016;14(8):e1002533. PubMed
- William Beaumont. Encyclopaedia Britannica. britannica.com
- International Scientific Association for Probiotics and Prebiotics. The ISAPP quick guide to probiotics for health professionals: History, efficacy, and safety. 2019. isappscience.org
- NIH HMP Working Group, Peterson J, Garges S, et al. The NIH Human Microbiome Project. Genome Research. 2009;19(12):2317-2323. PMC
- National Institutes of Health, Office of Dietary Supplements. Probiotics: Fact Sheet for Consumers. ods.od.nih.gov
- Gibson GR, Hutkins R, Sanders ME, et al. Expert consensus document: The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of prebiotics. Nature Reviews Gastroenterology & Hepatology. 2017;14(8):491-502. DOI
- Salminen S, Collado MC, Endo A, et al. The International Scientific Association of Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of postbiotics. Nature Reviews Gastroenterology & Hepatology. 2021;18(9):649-667. PubMed
- Insights into the enumeration of mixtures of probiotic bacteria by flow cytometry. BMC Microbiology. 2023. DOI (add authors from the article page)
