Let’s start at the very beginning: probiotics are bacteria. We know what you’re thinking, bacteria cause infections and are just generally kind of gross. Well, in some aspects, you’re absolutely right. But when it comes to your digestive and feminine health, some bacteria are teeny tiny miracle workers that can make all the difference in the way you feel!

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.


"There is an increasing interest in probiotic interventions," wrote the authors of one of the most recent studies, a meta-analysis of previous research in a recent issue of the Journal of the American Medical Association. Those researchers found that probiotics were particularly useful against a common gastrointestinal problem: antibiotic-associated diarrhea (AAD).
Today, most of the Japanese population begins the day with a warm bowl of miso soup, believed to stimulate the digestive system and energize the body. Made from fermented soybeans, rice or barley, adding a tablespoon of miso to some hot water makes an excellent, quick, probiotic-rich soup. The fermentation process can take anywhere from a few days to a couple of years to complete, and the end result is a red, white or dark brown paste with a buttery texture.
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.
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.
Very few women know that one of the leading causes of infertility, difficulties getting pregnant, and even painful periods stem from thyroid dysfunction. That’s why infertility specialists, obstetricians, and gynecologists alike often order thyroid testing at the first sign of trouble. Poor thyroid function is also linked to joint pain, unplanned weight-loss or obesity and heart problems and thinning skin among many other signs and symptoms.
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."
Jotham Suez, Niv Zmora, Gili Zilberman-Schapira, Uria Mor, Mally Dori-Bachash, Stavros Bashiardes, Maya Zur, Dana Regev-Lehavi, Rotem Ben-Zeev Brik, Sara Federici, Max Horn, Yotam Cohen, Andreas E. Moor, David Zeevi, Tal Korem, Eran Kotler, Alon Harmelin, Shalev Itzkovitz, Nitsan Maharshak, Oren Shibolet, Meirav Pevsner-Fischer, Hagit Shapiro, Itai Sharon, Zamir Halpern, Eran Segal, Eran Elinav. "Post-Antibiotic Gut Mucosal Microbiome Reconstitution Is Impaired by Probiotics and Improved by Autologous FMT." Cell (First published: September 6, 2018)  DOI: 10.1016/j.cell.2018.08.047
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.

Until recently, testing of probiotics by ConsumerLab.com found that some products had far lower amounts of live organisms than claimed on the labels. But in 2018, it found that 17 out of 18 products tested contained the amounts listed; none exceeded limits for heavy metal contaminants. In contrast, in 2016, a study in Pediatric Research found that only one out of 16 Bifidobacterium longum supplements tested contained the species named on the label.

The concept of probiotics is credited to Élie Metchnikoff, a Russian scientist born in the mid-1800s, whose work provided profound insights into immunology and microbes. He developed a theory about aging that over the years had been forgotten in mainstream medicine but is now embraced by many scientists: namely, that health is influenced by toxic bacteria in the gastrointestinal (GI) tract. He is said to have noticed that people who lived to be over 100 years old in the Balkan States and Russia drank sour milk, which we now call yogurt or kefir, every day. In fact, Bulgarian yogurt cultures even today are regarded as highly therapeutic.
What exactly do probiotics do? They are believed to protect us in two ways. The first is the role that they play in our digestive tract. We know that our digestive tract needs a healthy balance between the good and bad bacteria, so what gets in the way of this? It looks like our lifestyle is both the problem and the solution. Poor food choices, emotional stress, lack of sleep, antibiotic overuse, other drugs, and environmental influences can all shift the balance in favor of the bad bacteria. 
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