Chances are excellent that when you hear or see the word "bacteria," the associations and terms that come immediately to mind regarding these single-celled organisms are more or less the opposite of what you'd want in, say, a best friend or roommate: "disease," "infection," "sick," "bad."
This is perfectly warranted. Micro-organisms – bacteria, viruses, a few fungi and a scattering of protozoans, for example – are responsible for countless millions of human and domesticated-animal deaths over the course of history, right up to the present day.
In recent decades, however, microbiologists have been closely examining the role of bacteria in promoting, rather than destroying, health under certain conditions. These "good" bacterial cells – and often, the products in which they are included – are called probiotics, and they are all the rage as the second decade of the 21st century winds to a close.
How Do Bacteria Help Us?
First, understand that whether you like to think about it or not, your gastrointestinal (GI) tract is about the most bacteria-riddled environment imaginable. There are up to around 100 billion micro-organisms, or microflora, living along its length, starting right in your nose and mouth.
Most of these bacteria, which are simpler than human cells, reproduce by binary fission and represent about 500 distinct bacterial species, live in the human body the large intestine, which is considerably shorter than the small intestine ("large" in this context refers to diameter). E. coli is a rather notorious natural intestinal resident. A large number of helpful, or at least harmless, bacteria are also present on your skin.
If you want to live completely free of bacteria, then you need to find a way to exist on Earth without carbon, nitrogen and the ability to fully digest what you eat. Even if you don't yet know a great deal of biochemistry, chances are.
Bacteria... to the Rescue?
While the habitation of the body by pathogenic species of bacteria (that is, those known to cause disease) is a clearly unwanted circumstance, other species are not merely harmless, but helpful to human health – good bacteria. In fact, more of them are beneficial or neutral than harmful, but it is far easier to tell when harmful bacteria are causing problems in your gut than it is to discern their health benefits, including:
- Combating the activity of pathogens
- Aiding the digestive system
- Bolstering immune system function
As a result, some scientists and health advocates have argued that the proliferation of these micro-organisms should not only be tolerated, but encouraged through supplementation, in the same general way traditional antibiotics are used to reduce or eliminate harmful bacterial cells.
How Organisms Interact
When the presence of two types of organisms in the same environment is beneficial to one species while having no effect on the other, this is known as commensalism. This is contrasted with parasitism, in which one species benefits to the direct detriment of another, and mutualism, in which both species in the ecosystem derive a benefit.
Many of the bacteria living on or within the body exemplify this kind of arrangement; the bacteria obviously benefit from the situation because they enjoy free shelter of a sort, like the American "hobos" of the 19th and 20th centuries riding in empty train boxcars, whereas the host simply doesn't notice.
"Friendly" Microflora Examples
As previously stated, microflora can have specific benefits for both the host and bacterial species. Some of the specific known and purported activities of these "friendly" microflora, and by extension of the probiotics that feature them, include:
Treatment of Everyday Health Conditions
Obesity, depression and constipation are targets of probiotic foods and therapy. It's believed that delivering bugs orally into the GI tract could influence the behavior of that GI tract is perhaps intuitive. Some bacteria, after all, can cause diarrhea so severe that it is possible to die from dehydration (the toxin produced by the bacteria that cause the disease cholera, seen mostly outside the United States, is a prime example).
Whether the balance of microflora in your gut can really have a direct effect on mood remains an open question.
More Thorough Digestion of Certain Foods
The human diet typically boasts a number of elements that would be very difficult, if not impossible, for the unaided digestive tract alone to reduce to sizes that allow them to be absorbed. The cellulose in plant fiber, for example, is a mechanically hardy substance that no one would confuse with anything edible if he or she discovered it in isolation.
Thus, probiotics contribute to sound digestive health.
Production and Assimilation of Critical Micronutrients
Without GI flora, gut health would suffer, as the body would be unable to maintain sufficient levels of vitamin K, which is essential for proper blood clotting. (Think "K" for "koagulation," as the Germans spell it.) In addition, bacteria are required to synthesize biotin, a member of the B-vitamin family that is a cofactor in reactions that extract energy from macronutrients such as proteins and fats.
In addition to the trillions of bugs swarming around in everyone's GI tract, some 200 species of bacteria inhabit the skin. Because this organ is in continuous contact with the outside world, it encounters countless potential pathogens and is usually the first part of you to do so.
The normal microflora living silently on your skin in impressive numbers make it difficult for potential pathogens to gain a foothold there. In short, the enemy of your enemy is your friend.
Priming the Immune System
Exposure to bacteria that are not pathogenic, but that contain antigens on their surfaces sufficient to provoke a mild response from the white blood cells in your body, is one of the many ways your system begins to build resistance to bugs and other external threats early in life.
Why Do We Need Probiotics?
Think of yourself as the main ingredient in a roving stew of different chemicals and living things interacting with one another all day and all night. Or, if that seems a little rough, fancy yourself as being the gracious host of a party for tiny countless creatures, some of which can get out of hand and require you to intervene.
Up front, know that the consensus today is that if your system is already in balance in terms of the microflora on and inside you, then taking probiotics won't help and in fact may even hurt. In this way, then, probiotics are not materially different from any number of standard supplements and medications.
For example, you can take iron supplements that can help you conquer anemia. But if you take these supplements when your iron levels are already normal or above normal, you could damage your internal organs.
By the same token, taking certain steroids or other hormones can be medically necessary for those whose bodies fail to make them in adequate amounts (think diabetes and insulin), but people who take these to achieve supra-maximal levels for the purpose of improved athletic performance run the risk of not only sanctions from sports' governing bodies, but serious health complications as well.
Who (Maybe) Needs Probiotics
The main reason most people come to legitimately need probiotic foods or supplements – which are still widely relegated to the world of alternative medicine – is because they have been taking antibiotics for bacterial infections. On the surface, this perhaps seems ironic, but it actually makes sense.
If you take a given antibiotic medication and it does its job of wiping out the problem-causing invaders, there is an excellent chance that the drug has, in a sweep of collateral damage, also disrupted the balance of harmless or useful living organisms in your gut.
Probiotics can also be useful in even more "niche" situations, such as to prevent an intestinal infection called necrotizing enterocolitis in premature infants in the hospital setting, where bugs tend to run rampant even when the medical staff is careful. Also, some probiotics may help relieve the symptoms of irritable bowel syndrome (IBS), and inflammatory bowel disease (IBD), which are not only uncomfortable but can wreak havoc on people's lives by continually sending them to the bathroom during work and other activities.
So What Are Some Common Probiotics?
According to the 2012 National Health Interview Survey, about 4 million American adults, or 1.6 percent if the adult population, reported taking probiotics of some sort. This is increased about four times since a similar survey taken five years earlier. Global sales were approximately $35 billion in 2015, a number that was expected to almost double to $66 million by 2024.
Two of the most common probiotics are the Lactobacillus and Bifidobacterium species, such as L. rhamnosus and B. longum. (Taxonomy tip: These are the genus names, which is why they are capitalized, unlike the species name. See Homo sapiens for an especially close-to-home example.)
Another common but less popular organism is S_treptococcus_ thermophillus. Lactobacilli are found as active cultures in yogurt, and all of these can also be taken as over-the-counter (OTC) supplements for "general health," a practice that may be ill-advised in the absence of an indication for taking them.
Do Probiotics Work?
It's important here to keep in mind a number of caveats already mentioned.
That being said, yes, probiotics may work if you take the right one and you have a good reason for doing so. That may sound terribly convoluted and wishy-washy, but again, this makes them little different from any other OTC or prescription health aid. Simply put, you shouldn't take them blindly; at a minimum you will be wasting your money, and moreover, you invite problems in so doing.
A few of the conditions for which there is favorable data, post-antibiotic therapy and IBS, have been mentioned already. Perhaps the best established results to date have been seen with the use of Lactobacilli species to treat diarrhea in infants and children (not adults, however). Some data suggests that they may help in constipation, Crohn's disease and ulcerative colitis. They have shown at least some promise in maintaining urogenital health as well.
Personal Testimonials Are Not Evidence
Some of the perceived benefits of probiotics are, inevitably the result of a placebo effect whose magnitude typically cannot be measured. More importantly, the effect of a given probiotic preparation on someone else's body may not represent the effect the same probiotic has on your own physiology, yet another reflection of how medical therapy works in general.
In addition, the fact that someone you know swears by probiotics is not in itself a reason to embrace them yourself. Also, apart from the question of whether probiotics do what their proponents claim they do, some of these agents, rather than being merely inert, may actually cause harm, with their side effects often being fairly predictable based on the known actions of these substances.
Reasons to Exercise Caution
In 2018, researchers linked the use of probiotic supplements to "brain fogginess" and abdominal bloating. That same year, scientists found that consuming generic probiotics after a course of antibiotics could delay, rather than enhance, the return to normal levels of desirable gut bacteria.
The greater picture suggests that person-to-person variation in response to common probiotics may vary more widely than previously believed, and that in some folks, the bacteria in probiotics fail to even colonize the GI tract at all.
On the whole, while it is a reach to assert that probiotics are always ineffective in the absence of a strong indication for using them, most of their renown may arise from marketing efforts, rather than science. This is a good thing to keep in mind when it comes to any OTC product that seems to be trendy; don't dismiss its potential out of hand, but certainly investigate anything you elect to put in your body for health reasons.
- Scientific American: Do Probiotics Really Work?
- National Center for Complementary and Integrative Health: Probiotics: In Depth
- Harvard Medical School: Health Benefits of Taking Probiotics
- Science Daily: Human Gut Study Questions Probiotic Health Benefits
- Clinical and Translational Gastroenterology: Brain Fogginess, Gas and Bloating: A Link Between SIBO, Probiotics and Metabolic Acidosis
- Live Science Health: Could Humans Live Without Bacteria?
- National Center for Complementary and Integrative Health: 1.6% of U.S. Adults (3.9 Million) Used Probiotics/Prebiotics
About the Author
Kevin Beck holds a bachelor's degree in physics with minors in math and chemistry from the University of Vermont. Formerly with ScienceBlogs.com and the editor of "Run Strong," he has written for Runner's World, Men's Fitness, Competitor, and a variety of other publications. More about Kevin and links to his professional work can be found at www.kemibe.com.