Gut flora makes up 70 to 80 percent of the human immune system. Too much bad bacteria can inflame and destroy intestinal walls, enter the bloodstream, and trigger a multitude of health issues — constipation, depression, skin problems, autoimmune disease, and even bad breath. Adding good bacteria protects the digestive tract from the harmful bacteria in sugars, pesticides, and saturated fats.

Many women eat yogurt or insert it into the vagina to treat recurring yeast infections, a "folk" remedy for which medical science offers limited support. Oral and vaginal administration of Lactobacilli may help in the treatment of bacterial vaginosis, although there isn't enough evidence yet to recommend it over conventional approaches. (Vaginosis must be treated because it creates a risk for pregnancy-related complications and pelvic inflammatory disease.) Probiotic treatment of urinary tract infections is under study.
Many women eat yogurt or insert it into the vagina to treat recurring yeast infections, a "folk" remedy for which medical science offers limited support. Oral and vaginal administration of Lactobacilli may help in the treatment of bacterial vaginosis, although there isn't enough evidence yet to recommend it over conventional approaches. (Vaginosis must be treated because it creates a risk for pregnancy-related complications and pelvic inflammatory disease.) Probiotic treatment of urinary tract infections is under study.
Even for those without an urgent problem, probiotics can help with overall digestive management. Challa argues in his book, Probiotics For Dummies, that good bacteria help "crowd out" bad bacteria. That's because the intestine is lined with adherence sites where bacteria latches on. If the sites are populated with good-for-you microbes, there's no place for a harmful bacterium to latch on.

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.


Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.
While the logic behind probiotics might seem sound, it is clear that we have a long way to go before understanding the complexity of the microbiota and the effects—both good and bad—that probiotics might have. All individuals have a unique gut microbiome, and the effects of different bacteria on different people are likely to be highly variable; as such, probiotic use might even need to be personalised for optimal benefits. Commercially available products might not contain the correct strains or quantities of bacteria to provide benefits, and most probiotic supplements contain only single strains, vastly oversimplifying the complexity of the microbiota. While taking a supplement for improved health is certainly an attractive prospect, those looking to aid their gut microbiota might be better served by consuming a healthy, varied diet. In the meantime, rigorous clinical trials are needed to substantiate potential health benefits and to confirm whether probiotics are elixirs or just empty promises.
The two main species you want to look for are: Lactobacillus and Bifidobacterium. Within these two species, there are a lot of different strains. The strains we chose for our probiotic—Lactobacillus acidophilus, Lactobacillus plantarum, and Bifidobacterium longum—have been shown to help modulate the immune system, help with autoimmunity conditions (which affect most of my patients), and counter infections in the gut.
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.
A slightly more surprising result, however, seems to be the way that probiotics may impact some of the symptoms of autism. Autism and gut health have been discussed for some time, as patients with the disorder typically suffer from a large number of digestive issues. However, based on animal studies, it seems possible that altering the quality of gut bacteria might benefit not only the digestive system, but the abnormal behaviors in autism, too. In 2016, a case study of a boy with severe autism was reported. While being treated with probiotics for digestive problems, the patient spontaneously improved on the ADOS scale, a diagnostic rating system for people with autism. The score dropped from 20 down three points to a stable 17, and according to the report, ADOS scores do not “fluctuate spontaneously along time” and are “absolutely stable.”
Probiotics and raw fermented foods and drinks, such as sauerkraut and kefir that contain probiotic-like microbes, are very helpful for digestion. They help to keep your gastrointestinal tract at the proper pH for optimal digestion and help to break down foods. They also regulate the motion of your intestines so that food moves through at the proper pace.
Of course, your gut microbiome can only do this when it’s healthy and in balance, which is where probiotics come in. Since so many factors can deplete your beneficial bacteria—including everything from exposure to antibiotics in food or medication to spending too much time inside—supplementing with a premium probiotic is almost always necessary to maintain balance.
If you suffer from recurrent urinary tract infections and are interested in giving cranberries a try, pay close attention to labels! As tasty as they may be, cranberry juice cocktails are chock full of sugar and very rarely include the D-Mannose your body needs. Instead, look for all-natural and organic cranberry juices or opt for cranberry extract pills if the pure juice isn’t exactly your cup of tea.
As with other types of supplements, scientists are still discovering the full potential of probiotics. However, when taken regularly, it is believed that they help support digestive health by helping maintain the balance of beneficial and non-beneficial bacteria in your digestive tract. Having a natural balance of good bacteria in the digestive tract can help defend against occasional digestive issues. In addition, probiotics play an important role in supporting immune health, since 70% of the body's immune system is found in the digestive tract.∗
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