What Are the Best Probiotic Strains?

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.1

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.2

(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.3


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.4 L. rhamnosus also helps restore the gut barrier in kids with acute gastroenteritis.5 And in rats with leaky gut, yogurt improves gut barrier function.6 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.7

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.8

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.9 Another study found that B. lactis reduced symptoms in constipated adults.10

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.11 Probiotic-enhanced artichokes are probably my favorite incarnation of this concept.12

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.13 In kids with hay fever, L. paracasei reduced nasal itching, sneezing, and eye swelling.14

L. paracasei also reduces eczema, probably by strengthening the skin barrier and improving water retention.1516

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.17

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:18

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!

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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5 thoughts on “What Are the Best Probiotic Strains?”

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  1. I took VSL#3 off and on for GI issues. That particular brand was recommended by a physician. It did help, but it’s not a cure-all. That’s probably true of any probiotic. Possibly a better idea is to use them as needed in conjunction with an improved diet. Truth be known, you can probably accomplish the same thing by regularly eating homemade fermented foods like yogurt, kimchee, sauerkraut, etc.

  2. This is good to know. I have a daughter with gut issues, and I myself think I may have SIBO going on. I generally treat my own issues by eating a diet that is pretty low-carb, and I make my own sauerkraut and eat some daily. My daughter periodically begs sauerkraut from me, and also tries to stay low-carb. (I cannot get her to make her own sauerkraut!) I will try the specific strains, and see if it makes a difference. As I understand it, the homemade sauerkraut probably contains a high count of a broad range of lactobacilli.

  3. The one concerning hay fever is interesting. I’ve always suffered from it (less severe since primal, not gone though) and all my siblings do/did too. My daughter has severe eczema that I’ve been struggling to improve for years (she’s almost 4) and the probiotic you mentioned sounds worth trying. She used to eat a lot of sauerkraut until it was recommended by her doctor’s nutritionist to try removing histamine rich foods along with the dairy and eggs we cut out. Bringing them back in ramped up her itching a LOT so we just don’t do ferments anymore unfortunately. She’s still itchy though, just less frequent wake ups at night, and the appearance and texture of her skin hasn’t improved either. Eczema is exhausting…

  4. A few years ago, I read an article concerning which probiotics strains affect various neurotransmitters. I was intrigued by the ones that have an effect on GABA and its possibility of helping with my insomnia. Being at the gym and doing a more intense HIIT or going for a long run (6 miles) would result in two or three days of either being awake most of the night or neve I stopped taking it only to have two really good night’s sleep. Started taking it again and started sleeping well. Ran out and thought r reaching a really deep sleep. The best sleep I had ever had was when I was on Gabapentin for pain for shingles. (Going off gabapentin was the worst insomnia ever – two weeks of sleeping only 2 hours a night.) Lactobacillus acidophilus, Lactobacillus casei, and Bifidobacterium bifidum were the strains which were to help with GABA production. It was not an immediate solution to the insomnia. In fact, I thought it wasn’t working, so after 2 weeks ,and only 2 really good night’s sleep, I stopped taking it. What I didn’t realize was that my sleep quality had been gradually improving. I started taking it again and began to sleep well. I stopped again, thinking that the probiotics had built up in my gut, and I wouldn’t need them. Sleep deteriorated again. What I didn’t realize is that stress, physical or mental, can decrease the gut flora. I sleep very well most nights now no matter what the activity has been unless I’ve forgotten to take my probiotics for a few days (I’m horrible at remembering to take pills of any type.) Anyway, those Lacto and Bifido strains have really helped with the insomnia when nothing else I had tried over the years would help.

    1. Sorry about the fragmented comment. Touch pad on this laptop creates more inadvertent insertions that I fail to catch until it’s too late.