Because poor gut health is related to autoimmune responses like those found in rheumatoid arthritis (RA), probiotics have been a proposed treatment option for the condition. Only a few studies have been conducted in humans, and only one testing L. casei 01, a particular probiotic strain, was able to find a decrease in RA inflammation and progression of the disease.
Two dangerous diseases in newborns, necrotizing enterocolitis (NEC) and neonatal sepsis, may meet their match with well-designed probiotic supplements. Both of these conditions are common in premature babies and are most dangerous in low birth weight and very low birth weight infants. Research has confirmed that when a pregnant mother takes high-quality probiotics during pregnancy, her baby is significantly less likely to develop either NEC or sepsis, particularly when the baby is breastfed after birth (and mom is still taking the supplements) and/or when probiotics are added to formula. A probiotic supplement with multiple strains seems to be the most effective in these cases.
Yet that’s how probiotics are often offered. They can be distributed in the United States as food, supplements or drugs. The regulations for each are very different. Most people looking for probiotics don’t see the distinctions. Ideally, the ways in which we use and consume probiotics would conform to the data and evidence that back them up. That rarely happens.
You'd be right. Lebwohl said there are no current studies supporting probiotics for cancer, and further, that he’d be concerned about anyone with a compromised immune system using probiotics. “It has not been adequately studied for cancer and I would be concerned about widespread probiotic use in someone who might have a suppressed immune system due to cancer, because of the rare but documented instances of actual infections arising from probiotic use."
Tempeh is made with fermented soybeans or grains that have been molded into a cake-like form. The nuttier, tangier cousin to tofu can be sliced for sandwiches, tossed into stir-fries, or marinated and grilled. In addition to probiotics, tempeh contains about 15 grams of protein per half-cup and is a good source of iron. Plus, soy foods contain compounds that may help keep cholesterol in check, according to a study in The American Journal of Clinical Nutrition. Palmer likes to use tempeh in place of tofu in dishes like stir-fries, salads, and side dishes.
However, a 2003 pilot study and 2011 randomized, controlled trial both reported that RA activities remained unchanged, but the subjects treated with probiotics reported statistically significantly higher levels of “subjective well-being.” One suggested reason for this was that the trials were too short to establish changes in the observable changes in the internal earmarks of RA.
Uncontrolled changes in blood sugar levels or a decreased ability to regulate insulin can have serious effects on your overall health, and since far more men than women are at risk for these changes, these issues are well worth paying attention to.5 Research indicates that regularly taking probiotic supplements containing Lactobacillus and Bifidobacterium can help your body maintain blood sugar levels already within a normal range, whether you're simply at risk for insulin-related challenges or you're already experiencing them.
What’s more, RAW Probiotics are exactly what they purport to be – raw! They’re uncooked, untreated and unadulterated, and have no fillers or binders. You also won’t find any displeasing carriers, such as maltodextrin or dextrose. And since RAW Probiotics are kept in temperature-controlled cold storage through delivery and until they make it into your fridge, you can be sure your probiotics “arrive alive.”
Unlike many of the probiotics on the market today for women, Vitamin Bounty’s formula is fermented naturally and encased in a delayed-release capsule for more efficient digestion. Specifically, this capsule helps to protect the micro-organism strains from stomach acid, which can dissolve them before your gut has a chance to absorb all of their healthy goodness. With this Women’s Pro-Daily Probiotic design, you can expect more cultures and, as a result, fewer stomach upsets and feminine health problems!
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.
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.
In a food sensitivity, the immune reaction is delayed, usually several hours to days after the exposure. Food sensitivities are the most difficult to determine since there is not an immediate reaction. These kinds of issues with foods can cause a wide range of physical and mental problems. An elimination diet followed by reintroduction is one of the best ways to determine a food sensitivity.

Experts agree that this is the most important factor to consider in choosing a probiotic. "You should absolutely choose a probiotic based on what you are looking to address," says Chang. "Because strain specificity will impact outcomes, it is important to consider that one strain that works for one condition will not necessarily be effective for other conditions."
The other way that probiotics help is the impact that they have on our immune system. Some believe that this role is the most important. Our immune system is our protection against germs. When it doesn't function properly, we can suffer from allergic reactions, autoimmune disorders (for example, ulcerative colitis, Crohn's disease, and rheumatoid arthritis), and infections (for example, infectious diarrhea, H. pylori, skin infections, and vaginal infections). By maintaining the correct balance from birth, the hope would be to prevent these ailments. Our immune system can benefit anytime that balanced is restored, so it's never too late.
Update: I think this product is being smeared by a competitor! Look at all the reviews in April. Suddenly, a butt ton of not just negative but 1 star reviews. It's uncanny. So, what would compel a competitor to do such a thing? Well, it was the only 50 CFU, enteric coated & 20 strain probiotic on Amazon & it cost about 15 bucks. That, while products far inferior to it were priced for - often times - 2 or 3x as much.
When seeking out the best probiotic for you, consider your overall health, dietary needs, antibiotic use, GI challenges, and similar concerns. Then, review our list of the ten best probiotic supplements, which offer everything from raw probiotics, which must be refrigerated, to shelf-stable, slow-release probiotics that concentrate fewer CFUs in tiny, once-daily capsules.

Once the GI microbiome is disrupted, and especially if an infection is treated with antibiotics, it can take time for the resident microbiota to recover, if it ever does. A disrupted gut microbiome sets the stage for altered motility, intestinal hypersensitivity, gut immune activation, leaky gut, altered bile, mental disorders, and a host of other factors that can play a role in IBS. Good probiotics, along with a proper diet, can help the GI tract get the microbes it needs to function normally.
These statistics are staggering, yet poor gut health actually affects much greater numbers than these statistics illustrate because your digestive health affects every physiological system in your body. How is this such a complex system? Well, for one, the human microbiome contains 360 times more protein-coding genes than human genes themselves contain.
Sure, why the hell not? Lebwohl says: "Essentially a yeast infection is an overgrowth of a kind of fungus. In theory, a probiotic could potentially have an effect of the microbiome of the vagina, though proof of its effectiveness hasn’t really been established.” No harm in giving it a try as long as you don't succumb to the temptation to put yogurt in your vagina.

Myriad factors – antibiotics, diet, stress, and age, among them – affect the balance of diverse microbes present in your gut. While you can replenish your gut bacteria by eating well and incorporating natural probiotics (ex. yogurt and kefir) into a healthy diet, these processes can take weeks or months; taking a regular probiotic is an easy and effective way to ensure your gut (and immune system) stays healthy, always.
Digestive tract conditions. Probiotic supplements may be useful in treating and preventing inflammatory conditions, such as pouchitis (which affects people who have their colons removed), inflammatory bowel diseases (such as ulcerative colitis and Crohn's disease), and chronic stomach inflammation and ulcers caused by Helicobacter pylori bacterium. They may also be helpful in treating constipation, irritable bowel syndrome, acid reflux, spastic colon; shortening the duration of infectious diarrhea; and reducing the recurrence of bladder and colorectal cancer. Some studies suggest that yogurt is helpful in preventing diarrhea - a common side effect of treatment with antibiotics. It has also been shown to prevent or treat urinary tract infections and vaginal yeast infections in women.
“Some strains have been shown to help with GI complaints, some with immune function, and some even have been shown to have benefits outside the intestinal tract, such as with vaginal health or eczema,” says Gail Cresci, Ph.D., R.D., a Cleveland Clinic researcher who studies the microbiome. But there are few definitive conclusions from the current research.
Known as the most clinically proven effective probiotic strain, Lactobacillus rhamnosus GG (otherwise known as “LGG”) has been clinically proven to maintain healthy numbers of bacteria and yeast for optimal digestive health. This powerful probiotic is also paired with some of the best probiotic strains for feminine health, making it an ideal choice for any woman that is looking for complete care from her probiotic.
While more research is necessary to truly understand the widespread benefits of different probiotic strains, we do know that not all probiotics are created equal. The Lactobacilli, for instance, live in our digestive, urinary and genital systems and can be found in some fermented foods like yogurt. Bifidobacteria normally live in the intestines as lactic acid bacteria, and are also found in fermented foods. According to nutrition expert Alex Caspero, RD, “For certain conditions, you want to ensure you are taking the strand that is most likely to benefit you.” Here is a simple breakdown to help you determine the best probiotic for you.

I did the “milk test” on these New Rythm probiotics, along with Culturelle I had purchased in 2 different states (TX & MA, as I was traveling); my mother’s CVS brand acidophilus; and one “control” cup with milk only (so, 5 cups total in my experiment). The New Rythm became a solid yogurt consistency, while the other 4 remained liquids. I did the experiment twice, just to be sure of the results. I could not believe it!!! New Rhythm is my brand, hands down!!! I also would like to mention that my product usually arrives the day after it ships. So it will take a few days to ship when I select standard shipping, which is to be expected, but it doesn’t stay in transit long which is ideal for preserving the living cultures.
The U.S. Clinical Guide to Probiotic Products1, Canadian Guide to Probiotic Supplements2 and the WGO Global Guidelines for Probiotics and Prebiotics3 provide suggested effective amounts of specific strains for treating certain health conditions, such as constipation or IBS. All 37 products listed the species of bacteria they contained, but only 14 listed amounts of individual strains. We found that 9 of those 14 products provided beneficial bacteria at effective levels. The Center for Responsible Nutrition recommends4 the industry move toward specifying strains as a best-practice because whether a product works and for what purpose depends on its strains.
Most people with diverticulosis have few if any symptoms at all. When people do experience signs and symptoms of diverticulosis (diverticular disease) they may include abdominal pain, abdominal cramps, diarrhea, constipation, and bloating. Diverticulitis is a condition in which diverticuli in the colon rupture. The rupture results in infection in the tissues that surround the colon. Treatment methods for diverticulitis includes prescription medications, and in some cases, diverticulitis surgery.
The scientists discovered that the probiotics successfully colonized the GI tracts of some people, called the "persisters," while the gut microbiomes of "resisters" expelled them. Moreover, the persister and resister patterns would determine whether probiotics, in a given person, would impact their indigenous microbiome and human gene expression. The researchers could predict whether a person would be a persister or resister just by examining their baseline microbiome and gut gene expression profile.
To boost the immune system, B. Lactis is a promising choice. One study had participants taking either a probiotic or a placebo for 6 weeks. At the end of the period, researchers measured antibody levels and found greater increases in antibodies of the B. Lactis group than in placebo participants, concluding that this probiotic may help improve immune function [1]. In addition, a 2009 study found that supplementation of the strain B. Lactis DN-173 led to self-reported improvements in digestive comfort [2].
If you’re new to Bio-K+, know that each bottle contains 50 billion live and active probiotic bacteria. Probiotics are good for a wide variety of digestive issues, so it’s best to customize your dosage based on what your specific needs are. If you are looking to take a preventative dosage to support the health of your microbiome, start with a ¼ bottle per day. If you suffer from digestive health issues or regularly take antacids, start with a ½ bottle of Bio-K+ per day. If you have more serious gastrointestinal issues or have had to take antibiotics, Bio-K+ probiotics are great for getting your system back on track. Start with a full bottle per day and see how you feel (we’ve had amazing results from our fans!)
You may have heard some questions over whether SBOs are safe: The NIH has a presumed case report, which hasn’t been 100 percent verified, of someone with Lymphoma getting septicemia from taking a SBO (the organism B. subtilis). Some say that if you have leaky gut, you should heal it before supplementing with SBOs. If you are immunocompromised or have cancer, you can consult with a physician first to be safe.
For adult use only, this supplement also encourages a healthy intestinal system. It relieves gas, bloating, and constipation. Other wonderful aspects of this product include the following: It assists in nutrient absorption, it guarantees quality, and it has no artificial flavor, color, sweetener, lactose, milk, sugar, starch, preservatives, sodium, fish, yeast, wheat, gluten, or soy.
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.
If you’ve ever clicked on the 6:00 news or scrolled through the latest headlines on your smartphone, you probably know that supplements and vitamins are not typically backed by governmental entities like the FDA or the World Health Organization. This fact can leave supplement newbies a bit wary, which is exactly why we love the Garden of Life Dr. Formulated Once Daily Women’s Probiotic so much.
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.
Though capsules are ideal for quick, convenient consumption, powdered products are a great choice for anyone who wants to mix their probiotics with shakes or smoothies. The Hyperbiotics Organic Prebiotic Powder is a totally taste-free prebiotic powder that has inulin, FOS, resistant starch, and dietary fiber to help keep your gut health in line. Unlike probiotics, prebiotics works to nourish and grow the bacteria that is already in your body. This supplement also has acacia fiber, which is said to help suppress appetite and reduce gas and bloating. You can take between one and three scoops of powder a day, depending on how much microbial support you’re looking for. Each container comes with 375 grams or roughly 54 servings, and it doesn’t need to be refrigerated.
If you've ever been to an Indian restaurant, then you've probably seen a lassi—a smoothie made of milk, yogurt, fruit, honey, and cardamom. The drink goes well with spicy Indian food because it helps extinguish the fiery feeling in your mouth. If you want to try it at home, you can pick up bottles from brands like Dahlicious, which contain 15 billion live probiotics per serving and are available in flavors like mango and turmeric. Or, try this mango lassi recipe.
Every day, we’re exposed to toxins and inflammation-causing molecules from food and the environment that negatively impact digestion through pathways, such as leaky gut, known in the medical field as intestinal hyperpermeability. In leaky gut, the tight junctions that are supposed to keep disease-contributing compounds from leaving the digestive system are disrupted, allowing a lot of things through into the bloodstream that don’t belong there.
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.
In a separate study involving 21 healthy volunteers, also published today in Cell, the same group of researchers found that taking probiotics after treatment with broad spectrum antibiotics may actually delay the return of people's normal gut microbiome. This goes against the idea that probiotics can help "repopulate" people's gut bacteria after antibiotics wipe them out.

For Irritable Bowel Syndrome, patients who respond to a probiotic might take that in the long term, Lebwohl says, so as to maintain symptom control. With something like antibiotic-related diarrhea, you'd take it for a defined period of time until symptoms are gone. "This has been studied in children and adults and while study results have varied, meta-analyses suggest that probiotics can be protective in this context," he adds.
Probiotics One Daily Support is easily one of our favorite probiotics right now and currently sits at #2 in our ranking of the best probiotics supplements.  There’s a number of reasons why I like it so much, but the main one is I just felt SO much better while taking it!  My stomach (which sometimes gives me issues due to IBS) felt great and I had a bit more energy than usual.  I was also able to digest all my meals without any problems, a major plus!  Further, Daily Support is very allergy-friendly, doesn’t require refrigeration and comes with a 60-day guarantee.  So all-in-all, we gave Probiotics One 5 out of 5 stars and truly think it’s a REALLY great probiotic.  Read the full review here… or click here to go buy it now! 

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.

“Microbiome” refers to the trillions of bacteria and microorganisms that live on and in our individual bodies. “There’s increased recognition of the various ways that the microbiome affects our health,” Lebwohl tells me. “And with that recognition comes the true observation that many bacteria are good for us. This goes against the old idea that bacteria equal germs, which equal harm. It turns out that many bacteria keep us healthy and probiotics could potentially support that notion.”

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Experts agree that this is the most important factor to consider in choosing a probiotic. "You should absolutely choose a probiotic based on what you are looking to address," says Chang. "Because strain specificity will impact outcomes, it is important to consider that one strain that works for one condition will not necessarily be effective for other conditions."


According to a 2014 meta-analysis, probiotics benefit diabetics by improving insulin sensitivity and decreasing the autoimmune response found in diabetes. The authors suggest that the results were significant enough to conduct large, randomized, controlled trials (the “gold standard” of scientific studies) to find if probiotics may actually be used to prevent or manage diabetes symptoms. Combining probiotics with prebiotics may also help manage blood sugar, particularly when blood sugar levels are already elevated. (87)

However, this particular probiotic does not contain any additional vitamins, minerals, or plant extracts like some of the other brands we have reviewed. The Probiotic Pearls are a great option for women looking for an introductory probiotic or one with less fuss, but likely won’t pack the same punch as probiotics that include mineral blends and added vitamins in their formulas. This probiotic was also not designed to treat or prevent urinary tract problems, and may not be as suitable as other brands for women with recurrent urinary tract infections.
While past studies have investigated similar questions, they have all used patients' excrement as a proxy for microbe activity in the GI tract. Instead, Elinav, his colleague Eran Segal, (a computational biologist at the Weizmann Institute), and their teams spearheaded by Niv Zmora, Jotham Suez, Gili Zilberman Schapira, and Uria Mor of the Elinav lab collaborated with Zamir Halpern, Chief of Gastroenterology at the Tel Aviv Medical Center to measure gut colonization directly.
The benefit of taking a probiotic supplement is that a supplement contains very specific bacteria known to have a beneficial effect on human health, and a positive impact on our gut microbiome. Taking a probiotic supplement has the added benefit of providing a specific and concentrated dosage of healthy bacteria, so you know you are getting a therapeutic, research-proven dosage every time.

In the new study, the researchers analyzed information from 15 healthy volunteers who took either a probiotic product containing 11 strains of bacteria, or a placebo, for four weeks. The participants also underwent colonoscopies and upper endoscopies before they took the probiotics or the placebo, and again after the four-week treatment period. (An upper endoscopy looks at the upper part of the digestive tract.) During these procedures, the researchers took samples from inside participants' guts.
Most probiotics designed for women are designed to target feminine health conditions like yeast infections and urinary tract infections OR overall digestive health. While this may not be a concern for some women, the fact is that most of us can benefit from probiotics that keep our reproductive systems in check while also promoting overall digestive and immune health. That’s why we love the Culturelle Women’s Healthy Balance Probiotic: this women’s probiotic was specially designed to maintain feminine health without sacrificing the digestive and immune support of traditional probiotics!
Since feminine health is all about balance, it only makes sense that vH’s formula would also contain a healthy dose of probiotic cultures. These live bacteria work with the prebiotic formula and pre-existing bacteria in your system to create a thriving environment for your feminine health. These probiotics are particularly helpful at promoting vaginal and urinary tract health.

In the first study, 25 human volunteers underwent upper endoscopies and colonoscopies to sample their baseline microbiome in regions of the gut. 15 of those volunteers were then divided into two groups. The first group consumed generic probiotic strains, while the second was administered a placebo. Both groups then underwent a second round of upper endoscopies and colonoscopies to assess their internal response before being followed for another 2 months.

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.
Like other top probiotics available today, LEAN’s 50-Billion Probiotic is packaged in a handy, delayed-release capsule, designed to protect non-acid-resistant bacteria until they reach deep into your GI tract, where they’re most needed. The result is maximum effectiveness – better gut health, an immune boost, and relief of common digestive problems.
However, this particular probiotic does not contain any additional vitamins, minerals, or plant extracts like some of the other brands we have reviewed. The Probiotic Pearls are a great option for women looking for an introductory probiotic or one with less fuss, but likely won’t pack the same punch as probiotics that include mineral blends and added vitamins in their formulas. This probiotic was also not designed to treat or prevent urinary tract problems, and may not be as suitable as other brands for women with recurrent urinary tract infections.
In October 2013, the International Scientific Association for Probiotics and Prebiotics (ISAPP) organized a meeting of clinical and scientific experts on probiotics (with specialties in gastroenterology, pediatrics, family medicine, gut microbiota, microbiology of probiotic bacteria, microbial genetics, immunology, and food science) to reexamine the concept of probiotics. They define probiotics as "live microorganisms that, when administered in adequate amounts, confer a health benefit on the host." They also differentiated between products containing probiotics and those containing live or active cultures and established the following criteria:
I’m 65 years of age. I have been taking acid reflux medication daily for at least 15 years and recently my doctor said my kidneys were declining. I’ve read that acid reflux medications taken over a long period of time, can cause kidney damage. By taking a probiotic, will it help reduce stomach acid, where I may be able to stop taking my acid reflux medication altogether?
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.”
If you want to supercharge your probiotic friends, you may want to feed them with prebiotics. That’s P-R-E-biotics. They nourish the good bacteria in your gut in order to keep them healthy against the bad bacteria. They should go hand-in-hand with probiotics. Prebiotics are found in many foods, including bananas, whole grains, honey, garlic and onions. Try to get two to four servings of these prebiotic-rich foods a day.

Did you know that bacteria might actually keep you healthy? It all just depends on the type of bacteria. In this case, we’re talking about the benefits of probiotics. Probiotics benefits are some of the most widely researched natural solutions to gut health. For years, scientists and physicians have observed the many benefits of probiotics for not just the gut, but for the entire body.
If it sounds too good to be true, then it probably is. Taub-Dix recommends to err on the side of caution when purchasing probiotic food products that tout over-the-top claims. The Food and Drug Administration (FDA) doesn’t regulate probiotics as its own food group. Instead, they’re regulated based on the form they take on: dairy products, dietary supplements and powders, or medical foods.
The discovery of the benefits of probiotics began with sour milk. Today we have many other options to get various bacteria from our foods, although it's not as simple as just adding them to the food. For there to be health benefits, the microorganism has to be able to survive the passage through the gastrointestinal tract, survive the food manufacturing process, and grow and survive during the ripening or storage period. Also, the bacteria must not negatively affect product quality and be included on the Generally Recognized as Safe (GRAS) list.
For the generally healthy person, you can make a very good case to trust your own body to select and grow the best bacteria that are already in everyone. The foods you eat greatly influence your bacterial mix. Although probiotics offer many positive health benefits, there is no guarantee that they can make the trip from your mouth to your lower gut intact. Although adding more prebiotic fiber to your diet cannot guarantee safe passage of probiotics, it can influence the healthy bacteria that already live in your system. If probiotics help you, eating prebiotic foods or supplements will cause those healthy bacteria to flourish.

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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