Literally the best thing you can get for your body! I was having bad stomach problems and it vanished after two days of taking these regularly. Keep in mind that if you are putting junk into your body, you need good bacteria in your gut. It's crucial, roughly 80% of your immune system originates from your digestive tract. This WILL help you get your health back in order.
Dr. Vincent M. Pedre, medical director of Pedre Integrative Health and president of Dr. Pedre Wellness, is a board-certified internist in private practice in New York City since 2004. His philosophy and practices are a blend of both Western and Eastern medical traditions. He is a clinical instructor in medicine at the Mount Sinai School of Medicine and is certified in yoga and medical acupuncture. His unique methodology is best described as integrative or defined by a functional, systems-based approach to health. With his holistic understanding of both sides of the equation, he can help each patient choose the best course of action for their ailments to provide both immediate and long-term relief. His holistic approach incorporates positive, preventive health and wellness lifestyle choices. Dr. Pedre Wellness is a growing wellness platform offering health-enhancing programs along with informative social media and lifestyle products, such as dietary supplements, books, and weight-loss programs.
MegaFood is our only top pick that’s certified vegan, as well as being gluten free and dairy free, making it a good choice for any food-sensitive or vegan probiotic seeker. It has fewer of our wishlist “general health” strains than Vita Miracle, but it still contains five. This could be a go-to if you eat vegan, even if you’re not recovering post-antibiotic.
Supplements play an important role when the diet is not adequate to supply our needs. In the case of probiotics, one's diet is the ideal source for probiotics. These are live bacteria and need to be carefully monitored, stored, and combined for the health benefits that one would be taking them for. At this time, supplements are not monitored in the U.S. the way that food or medication is. They fall under the Dietary Supplement Health and Education Act of 1994 (DSHEA). This requires that the dietary supplement or dietary ingredient manufacturer be responsible for ensuring that a dietary supplement or ingredient is safe before it is marketed. The only time that the U.S. Food and Drug Administration (FDA) may get involved is if action is needed to be taken against a manufacturer after the supplement is marketed and then found to be unsafe. This means that as much as we may know about probiotics, we can't be certain of the safety or content of the supplements available to us.
Lactobacillus predominantly live in your small bowel (the portion of your gut that follows the stomach). Probiotics containing Lactobacillus sp. help to repopulate the small intestine with friendly organisms that aid in supporting digestion and immune function. The most beneficial are L. acidophilus, L. plantarum, and L. paracasei. One study found Lactobacillus acidophilus could reduce gut inflammation. L. rhamnosus helps increase GABA expression (an inhibitory neurotransmitter that helps you feel relaxed) in the brain, resulting in lower anxiety and depression-related behavior. Another found that a combination of Lactobacillus and Bifidobacteria (which we'll talk about next) improved symptoms of bloating in patients with functional bowel disorders, and yet another found that when people took the Lactobacillus rhamnosus GG strain, it significantly reduced the risk for antibiotic-associated diarrhea.
If you get sick often, probiotics might be the immune booster you've been looking for. The Cleveland Clinic says they've been shown to strengthen immunity by enriching and replenishing the good bacteria in the body. And when you eat foods with probiotics regularly, it's easier for your body to produce vitamins and enzymes that help keep your intestines happy.
Yogurt: It can contain Streptococcus thermophilus, Lactobacillus bulgaricus, L. acidophilus, and Bifidobacterium bifidum. Research has shown links with yogurt to have positive effects on the gut microbiota and is associated with a reduced risk for gastrointestinal disease and improvement of lactose intolerance (especially among children), type 2 diabetes, cardiovascular disease, allergies and respiratory diseases, as well as improved dental and bone health.
Taking a probiotic every day is a good way to help prevent getting sick and having to go on antibiotics in the first place. Preventative measures, of course, are preferred. Another that is believed to help is upping your vitamin D intake when your immune system needs a boost. Diet is also huge in terms of preventing sickness. Studies show that you can change your microbiome within hours of adjusting your diet. If you’re not into sauerkraut, even just cutting back on sugar and eating more whole foods can make a difference.

When shopping for a probiotic, the first things to look at are CFUs count and probiotic strains. CFUs is the acronym for colony forming units, and is the measure of how many probiotic bacteria are capable of dividing to form colonies. In other words, the higher the CFUs, the higher the number of active, live good bacteria. Generally speaking, the higher the CFUs, the better, although there are exceptions.
While this feature contributes to the efficiency of the product, it is unclear whether this product is vegetarian like some of the other probiotics we reviewed. Therefore, if you have any dietary restrictions or needs, this may not be the best probiotic for you and may, in fact, cause additional stomach upset or irritation. It is however gluten-free.
Given that you can get probiotics from the food you eat, you don't necessarily need to take a supplement, and Keatley says she prefers food sources of probiotics to supplements. However, she adds that "There are times when you really need a boost." One example might be during or after a course of antibiotics, as long as you have your doctor's OK, since antibiotics kill both good and bad bacteria: "Seeding your gut with good bacteria can lay the groundwork for a faster recovery and less constipation and diarrhea," Keatley points out. Angelone echoes Keatley's emphasis on food sources of probiotics, but also says that supplements can also play a useful role in "maintaining a healthy gut bacteria colony."
If you’re looking for a great probiotic you can take every day to target everything from gut to skin health, the Culturelle Daily Probiotic is our top choice. Each capsule has 10 billion active cultures of 100 percent Lactobacillus GG, a probiotic that helps curb gas, bloating, and upset stomach, and works to boost your immune system. Each capsule has the probiotic equivalent of 10 cups of yogurt and is dairy-free, sugar-free, and gluten-free. This container comes with 30 pills to be taken just once a day (most recommend taking it at night, especially when you’re just starting on probiotics).

An imbalance in the gut microbiota is believed to contribute to a number of health problems, particularly gastrointestinal issues, as well as immune dysfunction and infections. The bacterial balance can be disrupted by medical conditions, emotional and physical stress, and, most notably, use of antibiotics, which destroy the good bacteria along with the bad.
"Probiotics are live microorganisms which when administered in adequate amounts, confer a health benefit." 1 In general, probiotics are similar to the beneficial bacteria that live naturally in your digestive tract. When taken daily, probiotics can help support digestive and immune health. You may think of bacteria as something harmful to your body. But it's important to have a balance of good bacteria in your digestive tract, which can be negatively impacted from factors such as diet and travel. Probiotics are beneficial bacteria your body may need to support good digestive health.∗
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)
About 60 to 80 percent of our immune system lives in our gut. Imbalances in the gut’s microbiome (which is primarily made up of bacteria) lead to digestive issues, while many many other potential effects can be felt throughout the body—from feelings of fatigue to depression, thyroid dysfunction, autoimmunity, and a host of skin issues. Conditions like rosacea, psoriasis, eczema, and acne are really inflammatory conditions, and often a manifestation of something that is happening deeper within the body. When you fix the gut (which, depending on your health, might include getting rid of an infection like Candida, eating a clean diet, and taking a probiotic), skin issues often resolve as well.
There’s hard science saying probiotics can help with certain kinds of diarrhea, but for other conditions, it’s a bit of a crapshoot (har har). Lebwohl says that one of the first things that needs to change for probiotics to go widespread legit in the medical community is their regulation. Since they’re currently marketed as dietary supplements, they’re not subjected to the same FDA standards that medications are. That means that not only have they not been proven to work, it also means there’s also no assurance that what’s on the labels of these products actually matches what’s inside the bottle.

We are clearly getting to the strain level by going beyond “Saccharomyces boulardii” and to “Saccharomyces boulardii CNCM I-745”. They did a great job by actually putting it on the label so you don’t even have to contact the company to see exactly what strain you’re getting. (P.S. this is a well-researched strain that I highly recommend, especially for preventing antibiotic-associated diarrhea.)
Remember, while bacteria gets a bad rap, not all bacteria is bad: As New York City-based certified dietitian-nutritionist Gina Keatley tells Allure, plenty of microorganisms, including probiotics, actually help your body function. "Probiotics may help stabilize the protective barrier in our gut so bad microorganisms don't take root, stimulate the immune response, and aid in production of vitamins, such as vitamin K," she says. Sonya Angelone, a registered dietitian and Academy of Nutrition and Dietetics spokeswoman, adds that while we have more to learn about the role of probiotics, beneficial bacteria is understood to help crowd out harmful bacteria in our bodies. This good bacteria may also help lower cholesterol, aid in reducing colds and acute respiratory infections, and reduce the occurrence of vaginal yeast infections, she says.
Do you strain with infrequent bowel movements? Do the feces look like separate hard lumps or like bunches of hard lumps stuck together, or are they pencil-thin? You may have constipation. The Bristol stool chart (BSC) was developed by two doctors as a way to differentiate between states of constipation, normal elimination, a state of lacking fiber, and states of inflammation. Stools are supposed to be long and sausage-like, with few or no cracks in the surface.
Selecting a multi-strain probiotic is also consistent with the theory that filling your gut with enough good bacteria outcompetes any bad bacteria for the same space and resources. In your gut, the more diversified the good bacteria, the harder it is for the baddies to gain a foothold. With all this in mind, we only looked at supplements containing multiple strains of bacteria.
Selecting a multi-strain probiotic is also consistent with the theory that filling your gut with enough good bacteria outcompetes any bad bacteria for the same space and resources. In your gut, the more diversified the good bacteria, the harder it is for the baddies to gain a foothold. With all this in mind, we only looked at supplements containing multiple strains of bacteria.

Dr. Vincent M. Pedre, medical director of Pedre Integrative Health and president of Dr. Pedre Wellness, is a board-certified internist in private practice in New York City since 2004. His philosophy and practices are a blend of both Western and Eastern medical traditions. He is a clinical instructor in medicine at the Mount Sinai School of Medicine and is certified in yoga and medical acupuncture. His unique methodology is best described as integrative or defined by a functional, systems-based approach to health. With his holistic understanding of both sides of the equation, he can help each patient choose the best course of action for their ailments to provide both immediate and long-term relief. His holistic approach incorporates positive, preventive health and wellness lifestyle choices. Dr. Pedre Wellness is a growing wellness platform offering health-enhancing programs along with informative social media and lifestyle products, such as dietary supplements, books, and weight-loss programs.
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.
This dairy-free, gluten-free, vegetarian probiotic delivers live microorganisms, protected in stomach acid-resistant capsules to ensure effective delivery throughout your digestive system, from the stomach through your small intestines. The result is the repair and sustained maintenance of your intestinal micro-ecology, which in turn helps support healthy immune response and bowel regularity.
"The skin and the gut go hand in hand," explains Shapiro. "Since probiotics help improve the gut microbiome and aid in reducing inflammation, skin conditions will also improve. When eating a healthy, whole food diet as well, skin conditions get better over time. When the gut is not intact, other parts of the body also start to break down and become toxic. With probiotics, your gut becomes healthier and therefore, your skin problems start to disappear. "
The above line of probiotics is also a favorite of Engelman. "I like Nerium International's new Prolistic Pre & Probiotic Plus Vitamins ($45) because it combines prebiotics, probiotics, and vitamins," Engelman explains. "It supports overall health while targeting digestive function. It contains two types of prebiotics and two strains of probiotics to help enhance levels of beneficial microflora and balance levels of healthy bacteria in the digestive system. Additionally, it contains B vitamins, vitamin C, and vitamin D, which work to enhance the body's immune system and support natural energy production."

Unless you know that your body is lacking in a particular type of probiotic, you should just look for broad-spectrum probiotics that contain a mix of different strains of bacteria, Warren says: "We have billions of bacteria in our gut, so by taking a supplement with a range of different strains, you will ensure you are not overdoing or missing one type." Keatley also stresses the importance of finding a supplement with a diversity of bacteria strains to keep overgrowth of any one strain in check. "Providing too much of an advantage to one strain of probiotic may push out another strain we didn't know was important until it's too late," she points out.
Flora offers a high potency blend of eight super strain probiotics for general gut health and immune system support including multiple varieties of Lactobacillus and Bifidobacterium, among others. Containing up to 42 billion CFUs per capsule, this powerful health-boosting blend uses only strains found naturally in the human body, which increases its effectiveness.

In the gastrointestinal tract L. Plantarum can help regulate immunity and control inflammation. A 2007 study found that the probiotic could suppress an inflammatory response in the gut. Perhaps most significantly, a double blind placebo-controlled study over 4 weeks concluded that L. Plantarum 299v provided effective symptom relief, especially of abdominal pain and bloating, in patients with Irritable Bowel Syndrome [1].

If you get sick often, probiotics might be the immune booster you've been looking for. The Cleveland Clinic says they've been shown to strengthen immunity by enriching and replenishing the good bacteria in the body. And when you eat foods with probiotics regularly, it's easier for your body to produce vitamins and enzymes that help keep your intestines happy.


Amy Shapiro, MS, RD, CDN, founder and director of Real Nutrition based in NYC, discusses the effect probiotics have on immune system issues. "Probiotics compete with pathogenic microorganisms and produce chemicals that inactivate or kill pathogens," says Shapiro. "They help prevent immune-mediated diseases by improving the gut mucosal immune system. Overall, probiotics protect the body from infections and allow the body to maintain homeostasis."
Many studies have been conducted about the benefits of probiotics on a large number of health issues and conditions. Here, I’ll focus on the more thoroughly researched probiotics benefits, largely by sharing the results and data of meta-analyses on the subjects. Then, I have listed several areas of emerging research on the benefits of probiotics, reflected in small or pilot studies with promising results on probiotic benefits, as well as ways probiotics can be accessed.
However, these quality of life improvements are varied, and some improvements are quite mild. Sample group, types of allergies, symptoms, and results are across a broad spectrum. For example, numerous studies have shown that allergic rhinitis responses to the household dust mite decrease significantly in adults and children when probiotics were used. However, people allergic to birch pollen saw neither a decrease in general allergic responses to birch pollen or to apple food.
Unlike other probiotics on the market that are shelf stable, Garden of Life’s Raw Probiotics for Women are completely raw and alive at the time of delivery. In fact, these probiotics are so fresh that they are shipped in cold storage and delivery to keep all of those helpful cultures alive during transport and will need to be popped in your fridge immediately upon arrival.

"Probiotics applied topically sit on the skin's surface and prevent the skin cells from seeing the bad bacteria and parasites that can cause this immune system response," confirms Engelman. "This is known as 'bacterial interference,' as probiotics protect the skin and interfere with the ability of bad bugs like bacteria and parasites to provoke an immune reaction.
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Probiotics may seem new to the food and supplement industry, but they have been with us from our first breath. During a delivery through the birth canal, a newborn picks up the bacteria Bacteroides, Bifidobacterium, Lactobacillus, and Escherichia coli from his/her mother. These good bacteria are not transmitted when a Cesarean section is performed and have been shown to be the reason why some infants born by C-section have allergies, less than optimal immune systems, and lower levels of gut microflora.
Probiotic bacteria readily colonised the gut of everyone in the second group after antibiotics had cleared the way. However, the researchers were surprised to find that this prevented the return of the person’s normal microbiome for up to six months. “The probiotics very potently and persistently prevented the original microbiome returning to its original situation,” says Elinav. “This was very surprising and alarming to us. This adverse effect has not been described to date.”
After further analyzing the data, the researchers found that they could predict whether the probiotics would take hold in people's guts by examining their microbiome and gene expression in the gut taken at the start of the study. However, this prediction method needs to be confirmed in future studies. The researchers called for further research to better understand why some people resist colonization by probiotics, as that future research may enable researchers to counteract the resistance.
Eating foods rich in good bacteria and using probiotic supplements may help provide protection from inflammatory bowel diseases, including ulcerative colitis and Crohn’s disease. The evidence is stronger, however, for an improvement in ulcerative colitis, while Crohn’s disease may not benefit as greatly. In addition, there is ongoing research studying the role of probiotics in gluten issues, including celiac disease.
The good news keeps stacking up for probiotics, the good-for-you bacteria that keep your GI system functioning in tip-top shape. "Research is finding that a healthy microbiome may play a role in reducing inflammation, a risk factor involved in illnesses ranging from colds to cancer, heart disease, arthritis, and cognitive decline," says Katherine Tallmadge, RD, author of Diet Simple. In addition, the bacteria may help burn body fat and reduce insulin resistance, she says. So to stay slim and healthy, consider adding more probiotic foods to your diet. Start with these truly yummy 13.
The National Institute of Health (NIH) is sponsoring the Human Microbiome Project (HMP), which is developing research resources to enable the study of the microbial communities that live in and on our bodies and the roles they play in human health and disease. The NIH has funded many more medical studies using HMP data and techniques, including the role of the gut microbiome in Crohn's disease, ulcerative colitis, and esophageal cancer; skin microbiome in psoriasis, atopic dermatitis, and immunodeficiency; urogenital microbiome in reproductive and sexual history and circumcision; and a number of childhood disorders, including pediatric abdominal pain, intestinal inflammation, and necrotizing enterocolitis, a severe condition in premature infants in which the intestine tissue dies due to lack of oxygen.
“I’d probably stay away from store brands and pay a little extra for the name brand that’s been studied,” Dr. Cresci adds. “Ideally, look for a product that’s been tested for whatever you’re looking to address. It might say it helps with IBS, but you wouldn’t take that same product if you were taking antibiotics. You would want a product that helps with immunity. That’s where a lot of people get confused.”
D-Mannose can be naturally found in citric fruits like cranberries and has been found to be extremely beneficial in the prevention and relief of urinary tract infections. However, unless you are growing your own cranberries or spending hours in the kitchen measuring out portions, it can be extremely difficult (if not impossible!) to know how much D-Mannose you are ingesting by eating alone. That’s why HyperBiotics cut out the middle man and includes the D-Mannose compound directly in its probiotic blend.

Women’s health expert Dr. Amy Myers is a goop-trusted authority on subjects from autoimmunity and Candida to thyroid dysfunction; and she’ll be speaking IRL at our first wellness summit on June 10. Here, Myers helps us evaluate the increasing buzz around probiotics, and outlines the ins and outs of selecting a particular supplement (whether hers or other brands). Plus, we’ve rounded up our probiotic essentials, from inner beauty powders to favorite fermentation recipes, in one guide:


The idea that bacteria are beneficial can be tough to understand. We take antibiotics to kill harmful bacterial infections and use antibacterial soaps and lotions more than ever. The wrong bacteria in the wrong place can cause problems, but the right bacteria in the right place can have benefits. This is where probiotics come in. Probiotics are live microorganisms that may be able to help prevent and treat some illnesses. Promoting a healthy digestive tract and a healthy immune system are their most widely studied benefits at this time. These are also commonly known as friendly, good, or healthy bacteria. Probiotics can be supplied through foods, beverages, and dietary supplements.
An imbalance between good bacteria and pathogenic bacteria, yeasts or fungi, or a change in the bacteria species that colonize the digestive tract is called dysbiosis. It can have short and long-term effects on our body functions. These disruptions can reduce the immune system’s effectiveness, create unpleasant digestive symptoms (diarrhea, constipation, gas, etc.), be a contributor to certain chronic illnesses like obesity, and participate in producing pro-inflammatory metabolites.
That's because issues that can be treated with probiotics stem from specific imbalances in the amount of certain bacterial strains, according to Elena Ivanina, M.D., a gastroenterologist at Lenox Hill Hospital. "Therefore, if someone decides to supplement a particular strain of Lactobacillus, but they already have enough of that strain in their gut and their disease does not stem from a lack of Lactobacillus, then they will not have a response." Makes sense, right?
In the United States, most probiotics are sold as dietary supplements, which do not undergo the testing and approval process that drugs do. Manufacturers are responsible for making sure they're safe before they're marketed and that any claims made on the label are true. But there's no guarantee that the types of bacteria listed on a label are effective for the condition you're taking them for. Health benefits are strain-specific, and not all strains are necessarily useful, so you may want to consult a practitioner familiar with probiotics to discuss your options. As always, let your primary care provider know what you're doing.
Another study by Elinav and his colleagues suggests that not everyone’s gut reacts the same way to probiotic pills. They studied samples of microbiomes from antibiotic users before and after they took supplements for four weeks. The good bacteria were found in the digestive tracts of some people. But in others, the bacteria were present only in stool samples, not in their digestive tracts, where they’re thought to be needed to improve health.
Culturelle Probiotics, although very basic, is still a great probiotic supplement.  The results I got from trying it were positive– I felt pretty good throughout the entire trial period. Although this product only contains one strain of probiotic, the one they chose is a solid one.  The cell count is 10 billion, which is a good number for a daily probiotic.  Lastly, Culturelle doesn’t contain any frequently-irritating ingredients like milk, dairy or gluten.  Read the full review here… or click here to go buy it now!
Probiotics are live microorganisms (bacteria or yeast) that have been shown to have a health benefit for humans. They are available in supplement form or in probiotic foods and drinks. Probiotics are thought to be akin to (and to increase the level of) the "good" bacteria found in your intestines. These "good" bacteria are thought to enhance our health through their support of our immune systems.
Unless you know that your body is lacking in a particular type of probiotic, you should just look for broad-spectrum probiotics that contain a mix of different strains of bacteria, Warren says: "We have billions of bacteria in our gut, so by taking a supplement with a range of different strains, you will ensure you are not overdoing or missing one type." Keatley also stresses the importance of finding a supplement with a diversity of bacteria strains to keep overgrowth of any one strain in check. "Providing too much of an advantage to one strain of probiotic may push out another strain we didn't know was important until it's too late," she points out.
What about prebiotics vs probiotics? Prebiotics are the food fibers that go through the gut unchanged and are then used by good colon bacteria as a food source for their own growth. Everyone already has most of these good bacteria present, but often in small quantities. Prebiotics are used to stimulate their growth. Simply stated, you already grow your own probiotics within your colon. You do not rely on them to make the passage through the stomach acid — acid that can destroy many probiotic bacteria. That’s why taking a probiotic supplement or adding probiotic foods to your diet does not always help your digestive system. You can eat as many probiotic bacteria as you want, but if they don’t survive the trip to the colon, your effort will be fruitless. 

​​​​​​Lactobacilli dominate a healthy vaginal microbiota. Menstrual cycles, sexual activity, diet, certain medications, hygiene, and other factors can occasionally disrupt the vaginal microbiome. AZO Feminine Balance Daily Probiotic has been clinically demonstrated to contribute to the colonization of these important lactobacilli in the vagina.* The result: restoring the natural balance of good bacteria and yeast to maintain vaginal health.*

Some people prefer probiotic supplements over foods, but Dr. Cresci notes that probiotic foods are a better choice. In particular, fermented foods — like yogurt, kefir (a yogurt-like beverage), kombucha (fermented black tea), sauerkraut (refrigerated, not shelf-stable), kimchi (made from fermented cabbage) and tempeh and miso (made from fermented soybeans) — provide a nourishing environment in which healthful bacteria thrive and release an important byproduct: short-chain fatty acids.
Survival past stomach acids - probiotic powder in capsule form is ill prepared when it comes to protecting the delicate bacteria from being pulverized by the harsh environment of the stomach acids. Worse, most of the organisms tend to die off before they reach their intended destination due to moisture that gets trapped between the capsule shell and the powder.

Bacteria die out over time. Some supplements list the potency when they were manufactured (before they rode in a truck, sat on the shelf at the grocery store, or hung out in the kitchen cupboard for a few months). In this case, there could be dramatically fewer viable bacteria by the time you consume them than when they were first encapsulated, and good bacteria are no good to you dead.

Probiotics are found in everything from chocolate and pickles to hand lotion and baby formula, and millions of people buy probiotic supplements to boost digestive health. But new research suggests they might not be as effective as we think. Through a series of experiments looking inside the human gut, researchers show that many people's digestive tracts prevent standard probiotics from successfully colonizing them. Furthermore, taking probiotics to counterbalance antibiotics could delay the return of normal gut bacteria and gut gene expression to their naïve state. The research publishes as two back-to-back papers on September 6 in the journal Cell.
Even if some of the bacteria in a probiotic managed to survive and propagate in the intestine, there would likely be far too few of them to dramatically alter the overall composition of one's internal ecosystem. Whereas the human gut contains tens of trillions of bacteria, there are only between 100 million and a few hundred billion bacteria in a typical serving of yogurt or a microbe-filled pill. Last year a team of scientists at the University of Copenhagen published a review of seven randomized, placebo-controlled trials (the most scientifically rigorous types of studies researchers know how to conduct) investigating whether probiotic supplements—including biscuits, milk-based drinks and capsules—change the diversity of bacteria in fecal samples. Only one study—of 34 healthy volunteers—found a statistically significant change, and there was no indication that it provided a clinical benefit. “A probiotic is still just a drop in a bucket,” says Shira Doron, an infectious disease expert at Tufts Medical Center. “The gut always has orders of magnitude more microbes.”
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