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.”
In the second study, the researchers questioned whether patients should be taking probiotics to counter the effects of antibiotics, as they are often told to do in order to repopulate the gut microbiota after it's cleared by antibiotic treatment. To look at this, 21 volunteers were given a course of antibiotics and then randomly assigned to one of three groups. The first was a "watch-and-wait" group that let their microbiome recover on its own. The second group was administered the same generic probiotics used in the first study. The third group was treated with an autologous fecal microbiome transplant (aFMT) made up of their own bacteria that had been collected before giving them the antibiotic.
Here’s a quick timeline of the latest probiotic research that is setting off alarm bells for scientists around the globe: On June 19, a study was published linking probiotic use to brain fogginess and extreme belly bloating in some people. Another study, published on August 31, reported that consuming probiotics after taking antibiotics was linked to more severe intestinal infections in mice exposed to Cryptosporidium.  (For more see, "In a Brain Fog? Probiotics Could Be the Culprit" and "Unexpected Findings Cause Scientists to Rethink Probiotics.") 
If you’ve ever experienced the crippling pain of a urinary tract infection, you’ve probably encountered an article or two about the benefits of cranberries for warding off bacteria in the urinary tract. While it may seem like an old wives tale, cranberries contain D-Mannose that is naturally acidic. This compound has been said to prevent unwanted bacteria build-up, and some claim it can even stop a urinary tract infection dead in its tracks!
Probiotics are clearly incredibly supportive, but they can't do their work alone. To make sure that you're getting the most out of your microbes, it's important that you give them the support they need to work. You've got lots of options for supporting your gut health, from dietary changes to probiotic supplementation, but make sure you're at least covering the following bases.

Make sure to keep them away from moisture and heat which can kill off some of the microbes. I recommend taking on an empty stomach, ideally right when you wake up. You should always store supplements in a cool, dark place but refrigeration is best. Most of the strains of probiotics are fragile and should be protected from heat- so refrigeration is ideal. I recommend the probiotic Gut Instinct from HUM Nutrition for transparency and high quality.
Suez and colleagues investigated the recovery of the gut microbiota after antibiotic treatment and found that probiotics might perturb rather than aid this process. The probiotics rapidly colonised the gut but prevented the normal microbiota from repopulating for up to 5 months. While likely to be considerably less appealing, the group who received autologous faecal microbiota transplantation recovered their microbiota the quickest, with the composition of the microbiota returning to normal within days. Furthermore, Zmora and colleagues showed that colonisation occurred in highly individualised patterns, with some people's gastrointestinal tracts rejecting probiotics and others allowing colonisation by the probiotic strain, meaning that many individuals taking probiotic supplements are simply wasting their money.
​​​​​​AZO Complete Feminine BalanceTM is a daily probiotic supplement designed for the unique needs of women. Researchers that formulated the blend started by selecting species that are dominant in the healthy vaginal microbiota. Then they further refined the formula by selecting strains of probiotics that flourish in the vagina. The blend is clinically proven to help protect vaginal/feminine health.*
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