Candida yeast species, on the other hand, can cause numerous infections in and on you. Although they are usually present in controlled amounts, Candida overcomes your usual defenses and establishes itself when conditions are favorable, such as when you take antibiotics and many beneficial bacteria, which normally would control Candida, are killed. Unlike the Saccharomyces yeasts, which are not invasive, Candida species form hyphae, finger-like projections that penetrate tissues, causing deep infections that are difficult to eliminate. Candida is also able to weaken your immune defenses.
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.

When looking at the list of possible causes, it is no surprise that gut function plays a role in brain fog. The gastrointestinal (GI) tract is in direct and indirect communication with the brain, and microbes in the gut can affect, for better or for worse, the types of communication that occur between the GI tract and the brain. Additionally, harmful products from pathogens in the gut can travel to the liver, overloading the liver and causing toxins to be circulated to the brain and contributing to brain fog.
This story has played out before, most notably with vitamin supplements, which decades of research have revealed to be completely unnecessary for most adults and, in some cases, dangerous, correlating with higher rates of lung, breast and prostate cancers. But that has not stopped marketers from pushing another nutritional craze. According to a National Institutes of Health survey, the number of adults in the U.S. taking probiotics or their cousins, prebiotics (typically nondigestible fibers that favor the development of gut bacteria), more than quadrupled between 2007 and 2012, from 865,000 people to nearly four million. San Francisco–based business consulting firm Grand View Research estimates that the global probiotics market exceeded $35 billion in 2015 and predicts that it will reach $66 billion by 2024.
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. 

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.
This Korean staple relies on lactic acid fermentation (also called lacto-fermentation) to turn cabbage or other vegetables into a spicy, pungent side dish that's packed with vitamin C. Order it at Korean restaurants or buy it in the refrigerated section of your grocery store (King's Kimchi is widely available at Walmart). For some guidance on making your own, turn to The Art of Fermentation ($23; amazon.com). Then, use it to spike veggie-laden rice bowls, top on soup, or serve alongside meat.

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.


"Although all of our probiotic-consuming volunteers showed probiotics in their stool, only some of them showed them in their gut, which is where they need to be," co-senior author Eran Segal, a computational biologist at the Weizmann Institute, said in the statement. "If some people resist and only some people permit them, the benefits of the standard probiotics we all take can't be as universal as we once thought."
If you’re most interested in taking a probiotic supplement for overall gut health, I suggest starting with 30 to 50 billion CFUs. Take probiotics on an empty stomach once or twice a day for at least three months. After that time, reassess and decide if the benefits warrant continuing a maintenance dose of the probiotic supplement. However, if you have SIBO, beware of starting a probiotic too soon after your treatment. In this case, it’s best to work with a health practitioner on which probiotic is right for each stage of the treatment.

Then, study participants were divided into one group that consumed a standard probiotic strain available in commercial supplements and a control group that was given a placebo. After two months of treatment, the researchers found that some people were so-called “resisters” who expelled the gut microbiomes in probiotics; others were identified as “persisters” who successfully colonized the generic probiotic strains in their GI tracts.
Animals, including humans, have microbes inside them that benefit them in multiple ways. These microbes are in a loose sense like probiotics, but the definition of probiotics was established to designate those microbes that have been isolated, studied, tested in a laboratory dish and/or clinically in animals and/ or humans, and proven to have beneficial properties. In many cases their genetic fingerprints were sequenced for identification purposes and also to check for potentially harmful genetic components. The official term “probiotics” established specific criteria for scientific studies and probiotic supplements, foods, and drinks.
Probiotics stick around for a while, though for how long isn’t precisely clear. You have to keep taking them to continue to reap the benefits. Further, getting a wide variety of strains into your system is beneficial. “Periodically mixing up your probiotic supplement is also a good way to ensure that you get different health-building strains in your health regime,” says Dr. Cook.
They can break down substances in foods that keep you from absorbing the micronutrients inside. They not only protect against the consequences of rogue molecules passing through a leaky gut, but they assist your intestinal cells in staying healthy to optimize nutrient absorption. In addition, some of the metabolic by-products of probiotics, such as short-chain fatty acids and vitamin production, are very nourishing to your GI tract.
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:
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