Probiotics are everywhere. While this “good guy” bacteria can occur naturally in some food products (like yogurt and kefir), added probiotics can be found in everything from protein powders and flavored drinks to muffin mix and granola—not to mention the huge assortment of probiotic capsules, gummies, and powders you can find in your local pharmacy.
But what exactly is a probiotic? And, more importantly, do you need it?
The exact definition of probiotic itself is a bit nebulous.
It’s typically considered to be a live microbial species (or collection of species) that serve as “good” germs within your body. Usually these are meant to be gut organisms, which grow in your intestine and help with digestion. Probiotics are often bacteria, but they can also include some species of yeasts.
The idea that eating these “good” organisms can help with various health conditions has been around for a long time. Yogurt, for example, has frequently been recommended as a supplement to antibiotic use as a way to ward off diarrhea (since antibiotics can kill off both the germ that is making you sick, as well as the normal bacteria that live in your intestines, which can lead to bathroom issues). The thought was that ingesting probiotic bacteria in yogurt could help ameliorate this antibiotic-related diarrhea. But even though yogurt is often recommended, the jury is out on whether it actually helps or not.
Probiotics have received a considerable jump in popularity over the last few years as new studies seek to understand what’s called the human microbiome, or the collection of microbes that live in and on your body. The gut microbiome is the best-studied so far, containing some 39 trillion bacteria and more than 1,000 species, but microbes can also live on the skin, mouth, nose, and in the vagina. The goal of probiotic use is to alter the microbiome, either temporarily or permanently, in order to promote health. This could mean improving or eliminating an existing condition (such as Crohn’s disease, a chronic inflammatory bowel disease affecting the digestive system) or working to prevent a future one (like diarrhea due to antibiotic use).
Unfortunately, tossing back probiotics may not do anything in otherwise healthy people.
While they show considerable promise, clinical trials carried out so far have shown little impact from probiotic supplementation in healthy people. Some probiotic products have been marketed with vague claims, and even those don’t always stand up to testing. Dannon was sued by the Federal Trade Commission for the claims made about its Activia yogurt and DanActive drink. They had claimed that Activia, containing Bifidus regularis bacteria, could make bowel movements more regular, and improve “slow intestinal transit time.” DanActive, containing L. casei immunitas, was claimed to prevent colds and influenza and otherwise “help strengthen your body’s defenses.” None of these claims held up under scientific scrutiny.
Even without such claims on the label, yogurt is sometimes suggested as a “natural” treatment for health conditions, such as yeast infections. But evidence that it works is lacking. A number of clinical trials have tested bacteria from yogurt (primarily Lactobacillus acidophilus) as a preventive or treatment for conditions such as bacterial vaginosis or yeast infections. Though some showed moderate success, others did not, and these studies have generally been very small.
There are a number of reasons why probiotics might fail.
Jonathan Eisen is a microbiologist and professor at University of California, Davis who studies the microbiome. He tells SELF via email that “some ‘probiotics’ don’t actually have much living in them. They say they have microbes in them, but many of them are not viable.”
And because probiotics are considered dietary supplements, they’re regulated less stringently than drugs, which means they could contain contaminants, such as fungi or other species of bacteria.
And that’s just the first hurdle to clear. Even if the probiotic is what it claims to be, “the microbes still usually have to make it past the stomach into the gut to have any effect. Alas, depending on the microbe and how they are coated and treated and stored, many do not make it through the stomach,” Eisen says. So the probiotics that a consumer may be taking for intestinal upset might not even make it that far through the gastrointestinal tract.
For those bacteria that do survive the perilous journey through the digestive system, there can be some positive effects on the gut.
An animal study suggests this improvement is due to decreased intestinal inflammation. For patients with irritable bowel syndrome (IBS), a meta-analysis of probiotic trials in adults with the condition found that probiotics improved symptoms and overall quality of life, but the effect was small.
While this is promising, “gut health” in general is a buzzword that means very little. Because probiotics are not stringently regulated, the claim “improves gut health” may come from mere reports from individuals of increased bowel regularity or decreased gastrointestinal symptoms, but these reports were not rigorously investigated or determined to be due to the probiotics at all. Currently, there seems to be more hype than evidence in probiotic claims.
Indeed, many of the popular species of bacteria used in probiotic supplements, such as some strains of Bifidobacterium or Lactobacillus, aren’t natural inhabitants of the gut at all. Because they don’t typically live in the intestine, they may be killed by other native species of bacteria or by the host’s immune system. And while there may be some probiotics on the shelf that contain some actual gut natives, that’s probably not something most people are researching before they buy them.
There’s also promising research to suggest that certain types of probiotics could be tailored to treat certain health issues.
One successful use of probiotics has been in the elimination of recurrent infection by the gut bacterium Clostridium difficile, or C. diff. This is an infection that someone might get during a hospital or nursing home stay, but it’s also something that could be lingering in your gut normally and then get out of control after a course of antibiotics (which kill off the neighboring bacteria that normally keep it in check). It’s a hard to treat and even deadly infection, killing about 30,000people each year from complications of severe, long-term diarrhea, according to the Centers for Disease Control and Prevention (CDC).
Severalstudies have demonstrated the effectiveness of a probiotic mixture in curing C. Diffinfection through a fecal microbiota transplant (FMT). Because this starts with gut bacteria in their natural matrix (in other words, poop), it has a better chance of surviving in the gut. Plus, in the case of a poop transplant, you’re working with an already complex ecosystem of hundreds of species of bacteria, rather than a single strain. That said, this is obviously not the same as taking a probiotic supplement by mouth.
Another study shows promise in colonizing the guts of newborn babies. A recent clinical trial of newborns in India had to be halted halfway through enrollment because the probiotic supplementation was so successful, it was thought to be unethical to continue giving the other group a placebo. In this case, investigators used the species Lactobacillus plantarum, chosen because previous species they had tested (Lactobacillus GG and Lactobacillus sporogenes, both commonly used as probiotic supplements in India) showed almost zero gut colonization. Tests showed that L. plantarum, isolated from the stools of volunteers, effectively attached to gut cells, and when given to babies with a dose of sugar, reduced the incidence of newborn sepsis by 40 percent.
That may be the future of probiotics: carefully choosing and even engineering types of bacteria that are already well-established gut organisms and tailoring them specifically for certain types of health problems. Fecal donations could be encouraged and curated to see whose “poop profile” fits a particular condition, and stool could be frozen into capsules to minimize the “ick factor” of the procedure (which is usually done by mixing stool with saline and transplanting it via colonoscopy). Similar mixtures of bacteria could be added to the skin or the vagina for those who suffer from conditions like atopic dermatitis or bacterial vaginosis.
We’re not there yet, but we’re inching closer. In the meantime, save a few bucks and just buy the regular brownies.
Tara Smith, Ph.D. is an infectious disease epidemiologist and associate professor at the Kent State University College of Public Health.