What Are Gut Bacteria—and Why Do They Matter?

We’ve never talked more about the gut than we do today—and for good reason. Buzzwords like gut bacteria, microbiome and gut-brain axis point to a fascinating world inside our bodies that science is only just beginning to decode. Thanks to ongoing research, we’re learning more every day about the gut’s role in overall health. But what exactly do we know about bacterial strains—and what can they actually do?

What Are Probiotic Bacteria—and What Do They Actually Do?

Probiotic bacteria (or probiotics for short) are live microorganisms that can benefit the host—meaning us—when they reach the gut in sufficient quantities. You’ll find natural probiotics in fermented foods like yoghurt, kefir, sauerkraut, pickles, sourdough bread, tempeh and miso—as long as those foods aren’t overly processed or pasteurised. In recent years, probiotics have also become increasingly popular as supplements.

No matter the format—food or supplement—one thing matters most: it’s not just about what’s listed on the label, but whether the bacteria survive the journey and reach your gut. Only then can they actually have an effect.

What Does the Science Say About the Microbiome?

While this article focuses on the gut, the human microbiome goes far beyond digestion. In fact, the entire microbiome includes communities of microorganisms that live in the:

- Mouth
- Lungs
- Skin
- Gut
- Vagina

And from a genetic perspective, this internal ecosystem is massive—it carries over 150 times more genetic material than the human genome itself.⊕

Most of these microbes live in the gut, particularly in the large intestine, where trillions of bacteria form what’s known as the gut microbiome. But we’re not born with it. At birth, our digestive tract is sterile—it’s only after delivery that microbes begin to colonise the gut, through contact with the mother, the environment and later, food.

This internal world of bacteria lives in close symbiosis with us and plays several critical roles:⊕⊕

AG1 Upgrade: What’s Behind the 5 New Strains?

The human gut naturally hosts hundreds of different bacterial strains.⊕⊕ As science continues to uncover the importance of microbial diversity, supplement companies are working to increase the range of strains in their products.

That’s why the 2025 AG1 Upgrade now includes 5 clinically studied strains—adding more diversity to every serving of AG1.⊕⊕⊕ Here’s what you’ll find in every scoop:

• Lactobacillus rhamnosus GG is a well-documented lactic acid bacterium originally isolated from the human gut. It’s known for its ability to survive harsh environments like stomach acid. (Fun fact: the GG stands for the researchers who first described the strain—Sherwood Gorbach and Barry Goldin.) is one of the most widely studied acidophilus strains. A search for this strain on PubMed yields over 80 studies.

Learn more about our studies here.

The effect was measured using shotgun metagenomics—the gold standard for analysing microbial composition. Repeating these results across multiple trials strengthens their significance. It shows that AG1’s bacterial strains survive the digestive process and actually reach the gut. What’s more, our carefully selected whole food ingredients help these bacteria grow—and stay.

Probiotics vs Gut Bacteria—What’s the Difference?

Gut bacteria refer to the incredibly diverse ecosystem that lives in your gut. Probiotics, on the other hand, are a small and clearly defined subset of those bacteria.

Think of it this way: every probiotic is a gut bacterium, but not every gut bacterium is a probiotic. Probiotics are a select group with documented benefits—and only a fraction of the full microbiome.

You can get probiotics through food or supplements. When it comes to food, make sure it’s unpasteurised—as pasteurisation kills live bacteria. And when choosing a supplement, don’t just look at the total CFU (colony-forming units). Also consider the diversity of strains and whether they’re backed by research showing they reach the colon and have a real effect.

How to Support Your Microbiome—A Holistic Approach

Here are 5 practical ways to support your gut microbiome every day:

1. Eat more plants and fibre: Fibre is fuel for your gut bacteria and essential for good digestion. A plant-rich diet naturally includes plenty of it. Tip: stay hydrated to help your body make the most of those fibres.
2. Fermented foods: Try to get 1–2 portions of fermented foods daily (like sauerkraut, kimchi or yoghurt). You can also build a solid foundation with a clinically studied supplement like AG1.
3. Move your body: A sluggish body often means sluggish digestion. Reduce long periods of sitting and include more movement throughout the day. Fun fact: research suggests that physically active people have more diverse gut microbiomes.⊕
4. Prioritise sleep: Studies point to a two-way connection between sleep and the microbiome.⊕ So good sleep and recovery don’t just help you focus—they support your gut too.