No man is an island. If anything, every man is a sentient, mobile farm for the countless quadrillions of bacteria that colonize us. And by introducing the right bacteria into that equation, you can give your body one heck of a boost.
Every person on this planet could reasonably be considered a superorganism given that the number of microbes attached to us outnumber our own cell count 10 to 1, and routinely mix their genomes with our own. Each of us is a unique ecosystem with a unique blend of microbes coating their skin, mucus membranes, and gastrointestinal tracts.
Your gut alone hosts more than 100 trillion individuals from more than 500 species (half the body's total). Most of those actively work for your mutual benefit by keeping pathogens in check, helping break down food, and augmenting nutrient absorption, host cell development, and immune system function. You know, stuff that keeps you alive.
And how have we shown our thanks to these innumerable symbiotic helpers? From the advent of penicillin until the late 1990s, the medical community has waged a scorched earth campaign against microbes, applying antibiotics like napalm to patients' intestinal tracts. Which is great for killing off the disease-causing intruders, but those chemicals destroy beneficial microbes as well (often resulting in a wicked case of antibiotic-associated diarrhea). But a new spate of research suggests that instead of wholesale microbial genocide, we might be able to control the spread of harmful bacteria, eat more efficiently, and generally be healthier by actively ingesting copious amounts of the good kind, known as probiotics. Here's what we know so far.
Your gastrointestinal (GI) tract is not your own. It contains a menagerie of microorganisms working in conjunction with your body's own cells to process food and assist the immune system. Studies have suggested that we inherit many of these colonies from our mothers during our transit through the birth canal and via the ingestion of breast milk.
But while we know some of those bacteria are good and some are bad, we still don't have a solid definition of what constitutes a "healthy gut." While international organizations like the International Human Microbiome Consortium are studying the role that microbes play in our daily lives and how our bodies interact with them, we're still not entirely sure what they do, how they do it, or what the "optimal" mix of bacterial species would be (if there even is one). Heck, scientists can barely agree on even how the good bacteria beat out the bad—it could be by altering the microecology of the intestines (lowering the pH for example), producing natural antibiotics that poison the bad strains, or simply outcompeting them for food resources. We just don't know.
With so much left to discover about probiotics, the FDA has yet to weigh in on their safety which is why they're currently marketed as dietary supplements with the standard "has not been evaluated" warning. As such, any claims to their effectiveness should be taken with a grain of salt.
Probiotics are defined by the Food and Agriculture Organization of the United Nations (FAO) as "Live microorganisms which when administered in adequate amounts confer a health benefit on the host" and are most commonly found in fermented dairy products. That Activa yogurt Jamie Lee Curtis keeps going on about is loaded with Lactobacillus acidophilus, perhaps the most well known probiotic. Lactobacillus casei, Lactobacillus bulgaricus, Streptococcus thermophilus, Bifidobacterium, as well as certain strains of yeast, are all commonly used for human consumption.
People have been using probiotics since the advent of yogurt, though it wasn't until the start of the 20th century that Russian scientist and Nobel laureate Élie Metchnikoff first isolated a beneficial bacterial strain and suggested using probiotics to battle the effects of aging, which he attributed the growth of naturally occurring proteolytic bacteria such as clostridia and their production of toxic substances like ammonia while digesting proteins. He believed that these byproducts changed the basic function of the GI tract and resulted in the symptoms of old age.
Metchnikoff based this hypothesis on his observations of populations in Bulgaria and Russia that subsisted largely on fermented milk products (yogurt and cheese) and routinely outlived populations that did not. Metchnikoff suggested that the lactic acid loving bacteria in the milk products would take hold in the imbiber's gut, lowering the pH through their normal metabolic activities and prevent the growth of "harmful" proteolytic bacteria. And with that, he founded a new school of microbiology as well as a new business of selling a diet of sour milk fermented a bacterial strain dubbed "Bulgarian Bacillus."
Since probiotics are regulated as a food rather than a drug in the US, manufacturers can claim just about any benefit from probiotic bacteria that they wish so long as the include the FDA warning (which seems a pretty major loophole and a disservice to the American public by the agency charged with protecting its health).
However, a number of legitimate, peer-reviewed scientific studies have examined the bacteria's effects on the human GI tract with mixed results. The measurable benefits imparted by oral administration of the bacteria appear to be slight and temporary at best (conversely, fecal transplants have been shown to be a more permanent solution, though that procedure has yet to pass FDA certification). Either way, there is a growing body of results that suggest their effectiveness at treating any number number of GI diseases even if they don't provide causal evidence.
Antibiotic-associated diarrhea (AAD), for example, is caused when a course of antibiotics scrubs your intestines of all bacteria. This "changes carbohydrate metabolism with decreased short-chain fatty acid absorption" according to a meta-analysis study published in the Annals of Internal Medicine. The result: diarrhea, gas, and cramping. But ingesting probiotics such as Lactobacillus rhamnosus could help temporarily replace those decimated cultures until your natural contingent of bacteria grows back while keeping pathogenic bacteria in check.
Studies of vaginal yeast and urinary tract infections have also suggested a negative correlation with probiotic levels—the more good bacteria people have, the fewer infections they seem to get. Other studies have shown that ingesting certain active strains can increase a person's lactose tolerance, help control inflammatory bowel disease, and even stimulate production of IgA-producing plasma cells, T lymphocytes and Natural Killer cells.
Unfortunately, for these studies to be considered scientifically valid (and gain FDA approval), they must be conducted through randomized, double blind, placebo-controlled trials. Something nobody's quite figured out how to do yet.
Define safe. Yes, probiotics are found naturally occuring in our digestive system and have been part of European folk medicine for centuries. However, in some cases, these bacterial cures have killed.
In one such case, patients suffering from severe acute pancreatitis in a Dutch Pancreatitis Study Group trial were fed a mixture of six supposedly harmless probiotic strains. which promptly increased the patient death rate. Another study at the University of Western Australia administered probiotics vs a placebo to a group of 178 kids in their first six months to see if doing so could reduce their rate of childhood allergies. Quite the opposite, the kids that received probiotics were more likely to develop an allergy later compared the control group. Obviously, much more research is needed to determine how these cultures work for children and the seriously ill, so you probably shouldn't be feeding your kids or elderly parents probiotic supplements without first consulting a certified physician (sit down, Dr. Oz).
The real question is does it actually work? The answer is a resounding "sorta." Probiotic treatments can't permanently replace naturally occurring cultures and numerous studies have shown that the elevated levels of good bacteria drop back down to their original levels within a few days of stopping the treatment. Plus there's the whole problem with even getting viable probiotic cultures into your large intestines in the first place. Remember, the stomach is far too acidic for these bacteria survive (which is why they don't naturally occur there) so ingesting and expecting a majority of them to somehow survive until they reach their intended destination is just foolish.
So yes, probiotics are relatively safe, assuming you're a full-grown, healthy adult with an uncompromised immune system and the blessings of your primary care physician. For everybody else, you're probably best of waiting for the scientific community to finish weighing in. [FDA - IHMC - Web MD - Wikipedia - On Health - NIH - Harvard University - CDRF - CAST - Dannon - FAO (pdf) - Top art: Jill Chen / Shutterstock, State of the Gut: AP Photo/CDC / Janice Haney Carr, Pills: Mircea BEZERGHEANU / shutterstock, ]