What Are the Best Probiotic Strains?

“You should take probiotics.”

“I heard probiotics are good for you.”

“Oh, probiotics are so, so important.”

Yes, yes. These are all true statements. But they are broad. Which probiotics? Which strains for what purpose? Simply saying “probiotics” tells us very little about what we’re supposed to be taking. It’s like saying “You should eat food.” Technically accurate yet operationally useless.

Today I’m going to rectify that. I’m going to describe the best probiotic strains for each desired purpose, because there is no single strain to rule them all. The probiotic strain that’s best for anxiety may not be the best probiotic strain for allergies, and so on.

Of course, these aren’t the final word. What follows is the best available evidence as it exists today. That may change tomorrow. And it will certainly change based on your individual makeup.

With all that in mind, let’s get right down to it.

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Best Probiotic for Anxiety

The existence of the gut-brain axis — that mysterious thoroughfare running from the gut to the brain and back again — and the presence and even production of neurotransmitters along the gut suggests that “gut feelings” describe real phenomena. Mental and gut health are strongly linked, and it’s most likely a bi-directional relationship where each affect the other. You know this already, though, don’t you?

We’ve all felt fear or discomfort in our guts.

We’ve all had instinctual responses to certain people that seemed to manifest in our stomachs (and later be proven).

These are real. They aren’t figments of our imagination.

For instance, we know that some strains of gut bacteria can produce GABA, the “chill-out” neurotransmitter responsible for sleep and relaxation. We know that feeding prebiotics (bacteria food) to people can lower their cortisol and induce them to focus on positive stimuli instead of negative stimuli. We know that the greater the intake of fermented food like yogurt, kefir, kimchi, or sauerkraut, the lower the incidence of social anxiety.

The best candidate for anxiety is Lactobacillus rhamnosus. Although no human anxiety studies for this strain exist (yet), there are plenty of animal studies that support it. One notable paper found that dosing mice with L. rhamnosus increased cortical expression of GABA genes and reduced cortisol and anxiety-like behaviors.¹⁵

Best Probiotic for IBS

Irritable bowel syndrome is, well, irritating. Even more irritating is the fact that it describes a confluence of symptoms rather than a specific disease; two people, each with “IBS,” can have disorders with completely different etiologies. This complicates the probiotic you choose.

In one study, IBS patients who took a combo of Saccharomyces boulardii, Bifidobacterium lactis, Lactobacillus acidophilus, and Lactobacillus plantarum saw a 73% improvement in symptoms—but only if they also had small intestinal bacterial overgrowth (SIBO). IBS patients without SIBO only had a 10% improvement.¹⁶

(Side note: since gastro-esophageal reflux disease, or GERD, usually presents with SIBO, there’s a good chance that this lineup of strains could also help there)

Another paper, a meta-analysis from 2019, sought to determine which strains were best for IBS patients. While they didn’t come up with one prevailing strain, they did find that multi-strain probiotics generally worked better than single-strain probiotics, and that Lactobacillus acidophilus appeared in all the successful multi-strain studies.¹⁷

Get Primal Probiotics, which includes 4 of my favorite strains plus a prebiotic blend (food for friendly bacteria) to help them take root – all in one convenient capsule

Best Probiotic for Leaky Gut

The intestinal lining is not a passive, inert barrier but rather a dynamic, selective filter. Lining the gut are epithelial cells whose cell membranes fuse together to form protein complexes called tight junctions. The tight junctions serve as doormen: their job is to discern between what belongs inside and what doesn’t. In a perfect world, these tight junctions keep out pathogens, antigens, and toxins while admitting nutrients and water. But it’s not a perfect world, and sometimes the intestinal tight junctions are asleep at the post. Sometimes the gut is leaky.

Addressing leaky gut isn’t as simple as popping a few pills. Defeating it requires a multi-pronged approach, including sleep, diet, exercise, sun, and all the other regular lifestyle pieces I’ve covered in previous posts. But certain probiotic strains really do seem to help. In children with atopic dermatitis, for example, L. rhamnosus and L. reuteri supplements reduce leaky gut and improve symptoms.¹⁸ L. rhamnosus also helps restore the gut barrier in kids with acute gastroenteritis.¹⁹ And in rats with leaky gut, yogurt improves gut barrier function.²⁰ We aren’t rats, but yogurt is a safe bet (as is the Lactobacillus acidophilus that appears in most yogurts).

Best Probiotic for Diarrhea

Diarrhea after a round of antibiotics is a common side effect, especially in kids. A 2016 analysis of 23 studies of almost 4000 total pediatric subjects concluded that probiotics are effective at reducing the risk of antibiotic-related diarrhea, with L. rhamnosus and Saccharomyces boulardii as the safest bets.²¹

In adults coming off antibiotics, a combo of Lactobacillus acidophilus NCFM, Lactobacillus rhamnosus Lr-32, Bifidobacterium breve M-16V, Bifidobacterum longum BB536, Bifidobacterium lactis BL-04 and Bifidobacterium bifidum BB-02 was effective at reducing diarrhea.²²

Best Probiotic for Constipation

Among young college-aged women with constipation, a combo of Bifidobacterium lactis BL 04, Bifidobacterium bifidum Bb-06, Lactobacillus acidophilus, Lactobacillus casei, and Lactococcus lactis improved symptoms and quality of life.²³ Another study found that B. lactis reduced symptoms in constipated adults.²⁴

Other than that, the rest of the constipation/probiotic literature is pretty inconclusive and meager. What does seem to help is combining probiotics with prebiotics—ie, food for the gut bugs.²⁵ Probiotic-enhanced artichokes are probably my favorite incarnation of this concept.²⁶

Best Probiotic for Allergies

Probably the best anti-allergy probiotic strain is Lactobacillus paracasei.

L. paracasei has been shown to improve symptoms in subjects with hay fever across a number of studies. In adults with grass pollen hay fever, a fermented milk made using L. paracasei reduced nasal itching and congestion.²⁷ In kids with hay fever, L. paracasei reduced nasal itching, sneezing, and eye swelling.²⁸

L. paracasei also reduces eczema, probably by strengthening the skin barrier and improving water retention.²⁹ ³⁰

Best Probiotic for Immunity

The gut is in many ways the first line of our immune system. Some of the infectious diseases you don’t typically think of as gut-related can gain entry and spread via the gut. COVID-19, for example, often presents with gastrointestinal symptoms and researchers are examining whether probiotic supplementation can help reduce your risk of developing severe COVID.³¹

A meta-analysis of studies in elite athletes found a number of probiotic strains to be helpful in preserving immune function during extreme training. Athletes are a great population to study because their training places incredible stress on their immune systems; I remember back when I was running hundreds of miles a week, I’d constantly be coming down with something or getting over something else. So, which probiotics help?

Once again, the big names of the Lactobacillus and Bifidobacterium genera reign:³²

Lactobacillus paracasei

Lactobacillus acidophilus

Lactobacillus rhamnosus

Lactobacillus reuteri

Lactobacillus fermentum

Bifidobacterium lactis

Bifidobacterium bifidum

Overall, these strains from the Lactobacillus and Bifidobacterium genera are the best-studied for most applications. They’re often what appear in human guts and the fermented foods we’ve eaten for many thousands of years. It’s safe to assume that we’re well-adapted hosts to them.

There are so many more exotic strains out there. There are soil-based bacteria. There are strains unique to the Hadza hunter-gatherers of Tanzania. There are probably some interesting strains living in other traditional peoples in other regions. And I imagine many of them have potential to do us all a lot of good. But they may also have unwanted, unexpected effects.

The thing about probiotics is that you never really know which one will work best until you try. It’s a very personal thing. Each strain is going to react different to your unique intestinal ecosystem and genome. What we can say with fairly strong confidence is that probiotics are generally very safe. Not every strain recommended here will work for everyone, but luckily there’s not much harm in trying.

Which strains are your favorites? What have you tried? What hasn’t worked?

Let me know down below. Thanks for reading!

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