Twenty-one volunteers were given a course of antibiotics and then split into three groups. The first group were left to let the microbiome recover without any interventions, the second group were given probiotics and the third were given a fecal transplant of their own gut bacteria which was collected before the antibiotic treatment. The study found that the probiotics easily colonized the gut of the second group, but worryingly, rather than aiding the return of the normal gut microbiome, the probiotics actually significantly delayed it for months compared to both the group that had no intervention and the people who received a transplant of their own gut bacteria.
This is one of the newer areas of probiotic research. Described as the “gut-brain axis,” researchers believe that the communication between the gut and the brain affects not just physical but also mental health and behavior. For example, a recent study found that probiotics can reduce anxiety, relieve stress and improve mental outlook. Another study found that the probiotics L. helveticus and Bifidobacterium longum reduced depression, anger, hostility and self-blame and improved problem-solving ability. Another study showed a difference in brain activity between women consuming yogurt and those consuming a placebo. More research needs to be done to confirm the effect of probiotics on mental and emotional health.
Unless you have a perfect gut and are already eating lots of fermented foods—which is rare, although you can work up to this point—it’s difficult to get all the probiotics you need from diet alone. Most of us don’t have perfect guts—everything from antibiotics to high-carbohydrate diets to being born via a C-section can compromise the balance of bacteria in our microbiome. Supplementing with a probiotic can help to restore imbalances, and it’s also just a great preventative health measure, helping to keep your microbiome in balance and your immune system healthy to ward off illnesses.
To factor strain-specific benefits into our efficacy score, we referenced the information in these guides. Products were rewarded for containing strains on these lists. Additionally, measured levels of each strain were compared to what is thought to be effective based on these guides, and scores were scaled accordingly. In cases where products did not list strain-specific amounts, or their listed strains were not included in these guides, total measured CFUs were compared to a general effectiveness threshold of 1 billion CFUs cited by research published in the American Journal of Clinical Nutrition11.
Pure Therapeutics Power Probiotic 100B offers 100 billion CFUs of 4 powerful probiotic strains, including science darling, the HN019 strain of Bifidobacterium lactis. Since environmental factors, including moisture, oxygen and heat, can degrade the stability of your probiotics, Pure Therapeutics 100B is delivered in nitrogen-purged aluminum blister pacts, which ensure viability until the probiotic hits your system. No refrigeration is required.
While Lebwohl isn't comfortable endorsing a specific brand publicly, he did say "a widely used brand in which the compound is bifidobacteria or lactobaccilus seems like a reasonable way to go in a patient who is eager to give this a try, but would be best done under the supervision of a healthcare professional.” He does advise looking for a supplement with between 1 billion and 10 billion colony-forming units, or CFUs.
Best Probiotic says that Suprema Dophilus, manufactured and distributed by Vitabase, enjoys the highest customer rating in the market. Specially coated to help the bacteria spread through your entire digestive tract, its website claims over four billion viable cells per capsule, including five lactobacillus strains and three bifidobacteria cultures. Best Probiotic says that Suprema Dophilus also contains fructo-oligosaccarides to increase the life span of the bacteria.
Unlike MegaFood, the Renew Life label’s cold-storage recommendation is printed so small we nearly missed it (and it didn’t ship with a cold pack). If a probiotic requires refrigeration, be vigilant when buying it — the retailer that stores it or the company that ships it should keep it refrigerated until it gets to you. Otherwise, some of its potency might diminish in storage or transit.

The research also showed that while probiotics colonised the gastrointestinal tract of some people, the gut microbiome of others just expelled them. There was no way of telling from their stool sample which category people fell into. “Some people accept probiotics in their gut, while others just pass them from one end to the other,” says Elinav. They found that the probiotic colonisation patterns were highly dependent on the individual. That tells us that the concept that everyone can benefit from a universal probiotic bought from the supermarket is empirically wrong, he says.

Because there's a huge variety of probiotic products available on the market, many people struggle to find the right one for them. "There are many different strains of bacteria in different combinations within different probiotic supplements," explains Brooke Scheller, a clinical and functional nutritionist. "For example, a probiotic may contain a single strain of bacteria or many. It may also contain other vitamins, minerals, or other ingredients that may tout health benefits," she says. There are many different dosages, delivery systems (powder, tablets, capsules), and formulations (refrigerated vs. shelf-stable), and some probiotics also contain prebiotics, which basically act as fertilizer for the probiotics. (Related: Why Your Probiotic Needs a Prebiotic Partner)
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After the antibiotics had cleared the way, the standard probiotics could easily colonize the gut of everyone in the second group, but to the team's surprise, this probiotic colonization prevented the host's normal microbiome and gut gene expression profile from returning to their normal state for months afterward. In contrast, the aFMT resulted in the third group's native gut microbiome and gene program returning to normal within days.
We also found strains linked to five other health benefits like weight loss and lowering cholesterol. We feature options for those cases below, but they aren’t top picks because those use cases aren’t as heavily researched as immune health or IBS relief. Still, chances are any probiotic supplement is going to make some improvement to your digestive health, so don’t be afraid to experiment.
Most of the prebiotics identified are oligosaccharides. They are resistant to the human digestive enzymes that work on all other carbohydrates. This means that they pass through the upper GI system without being digested. They then get fermented in the lower colon and produce short-chain fatty acids that will then nourish the beneficial microbiota that live there. Oligosaccharides can be synthesized or obtained from natural sources. These sources include asparagus, artichoke, bamboo shoots, banana, barley, chicory, leeks, garlic, honey, lentils, milk, mustards, onion, rye, soybean, sugar beet, sugarcane juice, tomato, wheat, and yacón. The health benefits from these oligosaccharides is a topic of ongoing research.
The first major finding was that many people were essentially resistant to any effect from probiotics and their gut microbiome did not change after taking them.  Of 19 people in the study taking probiotics consisting of 11 of the most commonly found strains, only 8 had any notable colonization of their gut with the bacteria in the probiotics, with 3 people considered to have significant colonization and 5 people with "mild" colonization.
While one 2009 study did show some evidence for reducing cold and flu symptoms in children ages three to five and a 2015 analysis showed probiotics to be better than placebo in preventing acute upper respiratory infections, neither were enough to convince the National Institutes of Health of the efficacy of probiotics for colds and flu. The NIH confirms, “the evidence is weak and the results have limitations.”
In these cases, IBS is essentially just TMI. “For the colon to be functioning properly, it needs to be contracting and relaxing in a way that is conducive to regular bowel movements that occur at predictable times and don’t occur too frequently or too rarely," Lebwohl says. "And the bowel needs to be giving infrequent feedback to the brain. People should not be getting updates from their bowel in terms of cramps or the feeling of having to have a bowel movement too often. Yet, people with IBS get very frequent unsolicited ‘progress reports’ from the bowel.”
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"People have thrown a lot of support to probiotics, even though the literature underlying our understanding of them is very controversial; we wanted to determine whether probiotics such as the ones you buy in the supermarket do colonize the gastrointestinal tract like they're supposed to, and then whether these probiotics are having any impact on the human host," Eran Elinav said in a statement. "Surprisingly, we saw that many healthy volunteers were actually resistant in that the probiotics couldn't colonize their GI tracts. This suggests that probiotics should not be universally given as a 'one-size-fits-all' supplement. Instead, they could be tailored to the needs of each individual."
More and more evidence shows that the gut microbiota may play an important role in the development of obesity, obesity-associated inflammation and insulin resistance. Obesity and Type 2 diabetes are associated with changes in gut microbiota. Several studies describe differences between the microbiota of lean individuals and those who are obese. The potential for using probiotics in weight management and obesity and diabetes prevention is exciting.

The National Yogurt Association, who created this seal of approval, requires all yogurt manufacturers to include it on products that meet the standard of having a sufficient number of probiotics. The probiotics in store-bought yogurt need to meet this standard in order to be shelf-stable and reach your body alive. But even then, this standard isn’t all that useful in practice. The number just refers to the total number of live cultures and not the levels for each of those microbes. It’s possible, Taub-Dix says, that a product won’t have high enough levels of a certain probiotic to have any effect.

Keep in mind that when supplements contain a specific number of organisms, this number may not be what is actually within each capsule at the time of purchase. Probiotics are living organisms and can die out easily. Especially if that supplement sits on your drugstore or warehouse shelf for months or longer, the number of organisms you get may be far less than what the bottle claims. Hardier strains have a longer shelf life. Capsule strength decays faster if the probiotic has been sitting around at elevated temperatures during transport to the store. Companies actually have to produce probiotics with a much higher CFU (colony-forming units; see below) count in each capsule in order to guarantee the label potency by the expiration date.


Some foods are made by adding bacteria — yogurt, pickles, cottage cheese, kombucha, and sauerkraut are good examples. Those foods work to provide the same probiotic benefits as supplements. However, most foods are so processed and pasteurized that it’s unlikely you’ll see the same benefits, let alone the right strains, as you would with a supplement. Regardless, it can’t hurt to get extra probiotics through your diet.
Taking relatively high doses of these probiotic strains before, during, and after antibiotic treatment can help your microbiome get back on its feet: B. Lactis, B. Infantis, L. Acidophilus, L. Casei, L. Bulgaricus, L. Paracasei, L. Rhamnosus GG, and S. Boulardii. Our antibiotic combatant MegaFood MegaFlora has six of these strains, as well as eight others. One serving contains 20 billion CFUs to replenish the good bacteria.
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Coming in at a close second, our runner-up as the best probiotic for women is the Culturelle Women’s Healthy Balance Probiotic. As the #1 recommended brand by pharmacists, it is easy to see why so many women are turning to Culturelle for their digestive health. Featuring the LGG culture and a laundry list of other healthy bacteria, this probiotic offers a wonderful balance between digestive and feminine health. The Culturelle Women’s Healthy Balance Probiotic is also taken in an easy, chewable tablet and can even be taken during pregnancy, making it one of the most versatile formulas we reviewed!
B. Bifidum has also been shown to prevent intestinal pathogens or digestive disrupters from flourishing in the gut, essential in restoring the bacterial balance and optimizing digestion. Clinical research found it supports a significant reduction in IBS symptoms, an improvement in quality of life and even helps relieve occurrences of ulcerative colitis – a chronic inflammatory bowel disease. [1].
Drinkable Bio-K+ probiotics are unique in the world of probiotics. The innovative manufacturing makes Bio-K+ both a supplement and a fermented food, containing three strains of probiotic bacteria that you won’t find anywhere else. What does this mean for your health? It means that drinkable Bio-K+ probiotics are good for providing health benefits from your mouth to large intestine, working synergistically together from your first sip to improve your microbiota and support any instance of gut dysbiosis. 
Although these capsules are more expensive than other options on the market, if you suffer from ulcerative colitis, irritable bowel syndrome, or pouchitis, this probiotic will help manage your symptoms. VSL contains eight different probiotic strains (and more good bacteria than other brands) to alleviate symptoms such as bloating, cramping, and diarrhea. There are 60 capsules per bottle.

DNA-testing matches identity at a foundational, genetic level, so you know you’re getting the exact strains listed. New Chapter’s DNA-testing also verifies that you receive the specific strains researched for specific benefits: our strains boost immune defenses and enhance digestion, including bowel regularity and reducing occasional gas, bloating, diarrhea & constipation.*
Probiotics for allergies are fast becoming a preferred treatment method because they are understood to be much safer than traditional allergic rhinitis medication. A nasal spray for allergies is often a ‘go to’ treatment, for example, but allergy nose spray medications often contain corticosteroids, like Beclometasone dipropionate, which could affect bone metabolism, blood cells, and the pituitary gland.
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