Probiotics and Prebiotics: Do You Really Need Them? A Geriatrician Explains
Understanding gut health, beneficial bacteria, supplement labels, and what the science actually tells us.
During a recent class I was teaching on healthy aging, several students asked me about probiotics. Should they be taking one? Which brand is best? What is the difference between 10 billion and 50 billion bacteria? And what about prebiotics? Are those something we should be taking too?
These are excellent questions, especially considering how many products are marketed to us every day promising better gut health, improved immunity, less bloating, and even better brain function.
Walk into almost any pharmacy, and you'll find shelves filled with probiotic supplements. Some contain billions of bacteria. Others advertise 20 or 30 different strains. Some include prebiotics, and others claim to support the gut-brain connection.
And the prices can vary tremendously.
But here's something I want everyone to understand.
More bacteria does not necessarily mean a better probiotic. More strains do not necessarily mean better results. And not everyone needs to take one.
As a geriatrician, I spend a great deal of time reviewing medications and supplements with my patients. One of the questions I frequently ask is whether something is actually helping, whether there is evidence to support its use, and whether the potential benefits outweigh the risks.
Probiotics and prebiotics deserve that same consideration.
First, what exactly is the Gut Microbiome?
Our bodies contain trillions of microorganisms, including bacteria, viruses, and fungi. Many live in our gastrointestinal tract, where they collectively form what we call the gut microbiome.
These microorganisms play important roles in digestion, nutrient metabolism, intestinal barrier function, and regulation of the immune system.
Our gut microbiome also interacts with other systems in the body, including the nervous system. This is one reason researchers have become increasingly interested in the relationship between gut health, inflammation, metabolism, and cognitive function.
But there is an important distinction.
Knowing that the gut microbiome influences our health does not mean that taking a probiotic supplement will automatically improve our health.
These are two very different things.
Does Our Gut Microbiome Change as We Age?
Yes, although aging itself is only part of the story.
Our gut microbiome changes throughout life, influenced by diet, medications, physical activity, medical conditions, antibiotic exposure, and our environment.
In older adults, these changes may become particularly relevant because of factors such as:
Reduced dietary variety or inadequate fiber intake
More frequent antibiotic exposure
Multiple medications
Chronic medical conditions
Changes in gastrointestinal motility
Frailty, hospitalization, or changes in living environments
Researchers are studying whether some of these changes contribute to inflammation, metabolic dysfunction, frailty, and cognitive decline.
However, much of this research is still developing. We should be careful not to confuse an association with proof that a supplement can prevent or treat a disease.
What Are Probiotics?
Probiotics are live microorganisms that, when administered in adequate amounts, have been shown to provide a health benefit.
That last part is important.
Just because something contains live bacteria does not automatically make it a
beneficial probiotic.
Different microorganisms have different effects, and even closely related strains may
not provide the same benefits.
Some probiotics contain bacteria, while others contain yeast.
For example, Saccharomyces boulardii is a probiotic yeast that has been studied for certain gastrointestinal conditions.
Should Everyone Be Taking a Probiotic?
My answer is no.
For most generally healthy adults, there is not enough evidence to recommend taking a probiotic supplement every day simply to improve overall health.
That does not mean probiotics are useless. Certain strains may be beneficial for specific conditions.
The key is understanding what you are trying to treat or prevent.
For example, someone who develops diarrhea while taking antibiotics may have a different reason to consider probiotics than someone experiencing chronic constipation or bloating.
And a person who is immunocompromised or medically fragile may face risks that someone who is otherwise healthy does not.
I encourage my patients to think of probiotics as a potential targeted intervention rather than something everyone should automatically add to their daily routine.
When Might Probiotics Actually Help?
Let's look at some of the conditions people commonly ask about.
Antibiotic-Associated Diarrhea
Antibiotics can be lifesaving, but they can also disrupt the balance of microorganisms in our intestines. But some people develop diarrhea during or after antibiotic treatment.
Research suggests that certain probiotic strains, including Lacticaseibacillus rhamnosus GG and Saccharomyces boulardii, may reduce the risk of antibiotic-associated diarrhea in some populations. However, the benefits are not consistent across all age groups or medical conditions. Evidence of benefit in adults older than 65 is less convincing than in younger populations. Not everyone taking antibiotics needs a probiotic, and the decision should account for individual risk factors.
Clostridioides difficile (C. diff)
C. difficile is a bacterium that can cause serious diarrhea and inflammation of the colon, particularly after antibiotic exposure. Researchers have studied certain probiotic formulations to prevent C. difficile infection in people receiving antibiotics. Professional guidelines differ in their recommendations. The American Gastroenterological Association conditionally supports certain formulations for prevention in selected circumstances, while other guidelines recommend against routine probiotic use for this purpose. The evidence remains uncertain. Importantly, probiotics are not an established treatment for an active C. difficile infection and should never replace appropriate medical treatment.
Irritable Bowel Syndrome (IBS)
Some studies suggest that certain probiotics may improve symptoms such as bloating, abdominal discomfort, or irregular bowel movements. However, results have been inconsistent. The American Gastroenterological Association has concluded that there is insufficient evidence to recommend probiotics routinely for IBS outside clinical trials.
This is a good example of why we should not assume that all probiotics have the same effects.
Constipation
Constipation becomes increasingly common with age, often because of medications, reduced mobility, inadequate fiber or fluid intake, and changes in gastrointestinal function. Some studies suggest that particular Bifidobacterium strains may modestly improve bowel movement frequency or stool consistency. But the research is mixed, and probiotics are not considered a first-line treatment for most people with chronic constipation.
Before recommending a supplement, I would want to understand what is contributing to the constipation. Is it a medication? Is the person getting enough fiber? Are they physically active? Are they drinking an appropriate amount of fluid? Could there be an underlying medical condition? Sometimes the answer has very little to do with taking more bacteria.
Brain Health and Dementia
This is an area that has generated considerable interest.
You may have heard of the gut-brain axis, which describes the complex communication between our gastrointestinal tract, nervous system, immune system, and brain.
Researchers are investigating whether changes in the gut microbiome contribute to neuroinflammation, mood disorders, cognitive decline, and neurodegenerative diseases.
It is fascinating research, but we need to be careful about how we interpret it.
At this time, there is not sufficient high-quality evidence to recommend probiotic supplements for preventing Alzheimer's disease or other dementias. I would be very cautious about any supplement marketed as a way to prevent or reverse cognitive decline.
What Do 10 Billion, 30 Billion, or 100 Billion CFUs Actually Mean?
This was one of the most interesting questions my students asked.
When you look at a probiotic bottle, you will often see a large number followed by the letters CFU.
CFU stands for colony-forming units.
This laboratory measurement estimates the number of viable microorganisms capable of forming colonies under specific testing conditions.
For example:
1 billion CFU means approximately 1 billion colony-forming units.
10 billion CFU means approximately 10 billion.
50 billion CFU means approximately 50 billion.
100 billion CFU means approximately 100 billion.
You might assume that 100 billion would be ten times better than 10 billion.
But that is not how probiotics work.
A higher CFU count does not automatically translate into better results.
A probiotic's effectiveness depends on the specific microorganism, its strain, the dose studied, and the condition being addressed.
In some cases, a product containing one well-studied strain may be more appropriate than a supplement containing dozens of strains and a much higher CFU count.
There is another detail worth knowing.
Some products advertise their CFU count at the time of manufacturing. However, the number of viable organisms may decline during storage.
Ideally, the manufacturer should guarantee the stated CFU count through the expiration date, assuming the product is stored properly.
What Do All Those Different Bacterial Names Mean?
This is where probiotic labels become especially confusing. You may see names such as Lactobacillus, Bifidobacterium, or Saccharomyces boulardii. These names identify different groups of microorganisms. But there is another important distinction.
A probiotic can be identified by its genus, species, and strain.
Think of it as identifying a particular individual within a much larger family.
For example:
Lacticaseibacillus rhamnosus GG
Lacticaseibacillus is the genus.
rhamnosus is the species.
GG identifies the specific strain.
You may still see this organism listed under its older name, Lactobacillus rhamnosus GG.
That strain designation matters because much of the research on probiotics is strain-specific.
Two products containing bacteria from the same species may not have the same clinical effects. This is one reason I encourage people to look beyond the front of the bottle.
What About the Different Probiotic Brands?
Let's look at several recognizable products.These examples are for education, not endorsements or recommendations to purchase a particular brand.
Brand | Commonly associated microorganism | What to understand |
Culturelle | Lacticaseibacillus rhamnosus GG | A strain studied for certain types of antibiotic-associated diarrhea |
Align | Bifidobacterium longum 35624 | A strain studied for digestive symptoms, including some IBS symptoms |
Florastor | Saccharomyces boulardii CNCM I-745 | A probiotic yeast studied for antibiotic-associated diarrhea |
Visbiome | A specific multi-strain bacterial formulation | Studied particularly in certain gastrointestinal conditions, including pouchitis |
Other multi-strain products | Various combinations of microorganisms | Benefits depend on the exact strains, formulation, and condition |
Some brands sell several different formulations. Ingredients and doses can change, so it is important to read the label on the actual product. One product may contain a single strain, while another contains several strains. That does not automatically make one superior to the other. The question should always be whether the particular product has been studied for the condition you are trying to address.
What Are Prebiotics, and How Are They Different From Probiotics?
One of the things I want people to understand is that probiotics and prebiotics are not the same thing.
Probiotics are live microorganisms that can provide health benefits. Prebiotics are substances that beneficial microorganisms in our bodies use to support their growth or activity.
I like to explain it this way.
Think of your gut as a garden. Probiotics are like adding certain beneficial plants to that garden, while prebiotics are like providing the nutrients that help the garden thrive.
And here's something that may surprise you. You don't necessarily need to take a probiotic supplement to support the bacteria already living in your intestines.
You may be able to support them through the foods you eat.
Where Do Prebiotics Come From?
Many prebiotics are types of dietary fiber, although not all dietary fiber qualifies as a prebiotic.
Some common sources include:
Food | Prebiotic or fermentable components |
Garlic and onions | Fructans, including inulin and fructooligosaccharides |
Leeks and asparagus | Inulin-type fructans |
Oats and barley | Beta-glucans and other fermentable fibers |
Beans and lentils | Resistant starch and fermentable oligosaccharides |
Slightly green bananas | Resistant starch |
Cooked and cooled potatoes or rice | Resistant starch |
Chicory root | Inulin |
Not every fiber in these foods meets the formal definition of a prebiotic, but these foods can help support a diverse and healthy gut microbiome.
What Are the Benefits of Prebiotics?
When certain gut microorganisms ferment prebiotic fibers, they produce compounds called short-chain fatty acids.
One of these, butyrate, is particularly interesting because it serves as an important energy source for cells lining the colon and helps support intestinal barrier function.
Prebiotics may also influence bowel regularity, mineral absorption, and aspects of metabolic and immune function.
However, the benefits depend on the specific prebiotic, the amount consumed, and the individual. We cannot assume that every prebiotic supplement will improve every aspect of gut health.
Should You Take a Prebiotic Supplement?
Not necessarily.
For many people, I would start with food.
Eating a variety of fiber-rich plant foods provides more than just prebiotics. These foods also contain vitamins, minerals, and other compounds that support overall health.
If your diet is low in fiber, increasing your intake gradually may be a reasonable starting point.
But there is an important caution.
Prebiotics can also cause gas, bloating, and abdominal discomfort, especially when introduced too quickly.
People with irritable bowel syndrome, significant bloating, or sensitivity to fermentable carbohydrates may find that certain prebiotics, particularly inulin and fructooligosaccharides, make their symptoms worse. And for people with suspected small intestinal bacterial overgrowth, I would recommend discussing prebiotic supplements with their physician before starting them.
What About Synbiotics?
You may also see products labeled as synbiotics.
These contain both live microorganisms and substances intended to support beneficial microbial activity.
The idea is to combine the microorganisms with a substance they or other beneficial microorganisms can use.
It sounds appealing, but once again, combining ingredients does not automatically make a product more effective.
The specific formulation needs to be studied for the intended health benefit.
A Quick Comparison
Probiotics | Prebiotics | |
What are they? | Beneficial live microorganisms | Substances used by beneficial microorganisms |
Main purpose | Introduce specific microorganisms | Support microbial activity |
Examples | Certain Lactobacillus and Bifidobacterium strains | Inulin, FOS, GOS |
Food sources | Yogurt with live cultures, kefir | Garlic, onions, asparagus, certain fibers |
Supplements available? | Yes | Yes |
Potential downsides | Bloating, gas, rare serious infections | Bloating, gas, abdominal discomfort |
What About Yogurt, Kefir, Sauerkraut, and Other Fermented Foods?
Fermented foods can be a valuable part of a healthy dietary pattern.
Examples include:
Yogurt containing live and active cultures
Kefir
Kimchi
Refrigerated, unpasteurized sauerkraut
Miso
Tempeh
However, not every fermented food contains live microorganisms when it is consumed, and not every live microorganism qualifies as a scientifically established probiotic.
Some products are heated or pasteurized after fermentation, which can eliminate live cultures.
Still, fermented foods can contribute nutrients and dietary variety, and some may provide beneficial live microorganisms.
I generally encourage people to consider their overall dietary pattern rather than relying on a single supplement to improve gut health.
For many older adults, getting enough dietary fiber, maintaining adequate nutrition, and eating a variety of plant foods may be more useful starting points.
Of course, people with swallowing difficulties, food intolerances, dietary restrictions, or certain medical conditions may need individualized recommendations.
Can Probiotics Actually Be Harmful?
Yes. And I think this is one of the most important parts of the conversation, especially for older adults.
We often assume that because a supplement is natural, it must be safe.
But natural does not always mean harmless.
For most healthy people, probiotics are generally well tolerated. However, side effects and more serious complications can occur.
Common Side Effects
Some people experience:
Increased gas
Bloating
Abdominal discomfort
Changes in bowel movements
Diarrhea or constipation
These symptoms may be temporary, but they can also indicate that a particular product is not well tolerated.
If symptoms worsen after starting a probiotic, I would not recommend simply continuing it indefinitely in the hope that things will improve.
More Serious Risks
Although uncommon, probiotics have been associated with serious infections, including bacteria entering the bloodstream, known as bacteremia, and yeast entering the bloodstream, known as fungemia.
These complications are particularly concerning in people who are severely ill or have weakened immune systems.
I would be especially cautious in people who:
Are receiving chemotherapy or other significant immunosuppressive treatments
Have a severely compromised immune system
Are critically ill or hospitalized with a serious illness
Have central venous catheters
Have significant intestinal barrier damage or certain serious gastrointestinal disorders
Are medically fragile with multiple complex conditions
For example, Saccharomyces boulardii is a yeast. Although it may have benefits in selected situations, cases of serious bloodstream infections have been reported, particularly in hospitalized or immunocompromised patients.
This is not meant to frighten people. These complications are uncommon, but they are important.
For an older adult with several medical conditions, I would never assume that adding another supplement is automatically beneficial.
There are also quality concerns.
In the United States, most probiotic supplements are regulated as dietary supplements rather than medications. They generally do not undergo the same premarket approval process required for prescription drugs.
Products may differ in quality, strain identification, viable organism counts, and manufacturing standards.
This is another reason to discuss supplements with a healthcare professional rather than relying solely on advertising or online reviews.
Can Probiotics or Prebiotics Make Bloating or Small Intestinal Bacterial Overgrowth Worse?
Sometimes.
People with chronic bloating, abdominal discomfort, or suspected small intestinal bacterial overgrowth, commonly called SIBO, should be particularly careful about experimenting with multiple probiotic or prebiotic products.
Probiotics can increase gas or bloating in some individuals, although they do not necessarily cause SIBO.
The evidence regarding probiotic treatment for SIBO is limited and inconsistent.
Some products also contain prebiotic fibers, such as inulin, which may increase gas production in susceptible individuals.
If you already struggle with significant bloating or unexplained gastrointestinal symptoms, I would recommend discussing those symptoms with your physician before adding a probiotic or prebiotic supplement.
The goal should be to understand what is causing the problem, not simply to keep adding supplements.
Why Is It So Important to Talk With Your Doctor Before Taking a Probiotic?
I want to emphasize this point because I think it is often overlooked.
Probiotics are widely available without a prescription, and many people assume that means they are safe for everyone.
But supplements can have risks, and those risks may be greater in people with certain medical conditions.
As we age, we are more likely to develop chronic illnesses, take multiple medications, or experience changes in our immune system.
A supplement that may be relatively low risk for one person could be inappropriate for someone else.
For example, someone who is undergoing chemotherapy, taking immunosuppressive medications, recovering from a serious illness, or living with a central venous catheter may be at greater risk of complications from live microorganisms.
Even for otherwise healthy individuals, a probiotic may cause gastrointestinal symptoms or simply provide no meaningful benefit.
Another concern is that people sometimes use supplements to manage symptoms that deserve a medical evaluation.
Persistent diarrhea, unexplained constipation, abdominal pain, weight loss, or changes in bowel habits should not automatically be treated with an over-the-counter product.
Sometimes these symptoms are related to medications, nutritional deficiencies, infections, inflammatory conditions, or other medical problems.
And occasionally, they can be signs of something more serious.
I would much rather identify the underlying cause of a symptom than have someone spend months trying different supplements while an important medical condition goes unrecognized.
This is why I encourage people to discuss probiotics and prebiotics with their physician before starting them.
Your doctor can help determine whether there is a reasonable indication, whether a particular product has evidence supporting its use, and whether the potential benefits outweigh the risks in your individual situation.
Five Questions to Ask Before Buying a Probiotic or Prebiotic
Before spending money on one of these supplements, I encourage you to consider five questions.
1. Why am I taking it?
Is there a specific medical condition or symptom you are trying to address?
2. Is there good evidence for the particular product?
Research involving one probiotic strain or prebiotic ingredient cannot automatically be applied to another.
3. Do I understand what is actually in the product?
For probiotics, look for the specific strains, CFU counts, expiration date, and storage instructions. For prebiotics, look at the type and amount of fiber or other active ingredients.
4. Could this supplement be harmful given my medical conditions or medications?
This is particularly important if you are immunocompromised, medically fragile, or living with several chronic conditions.
5. Have I discussed it with my physician or another qualified healthcare professional?
Your clinician can help determine whether there is a reasonable indication, which product has supporting evidence, and whether the potential benefits outweigh the risks.
If you and your clinician decide to try one, establish what improvement you are looking for and when you will reassess whether it is helping.
There is no reason to continue spending money indefinitely on something that has not demonstrated a meaningful benefit.
My Approach as a Geriatrician and Lifestyle Medicine Physician
When someone asks me whether they should take a probiotic, I usually start by asking why.
Are they experiencing diarrhea? Constipation? Bloating? Are they taking antibiotics? Are they trying to improve their immune system? Or did they simply see an advertisement suggesting that everyone should take one?
Those are very different situations.
I also want to know what medications they take, what medical conditions they have, and whether they are already taking several supplements.
One of the principles I emphasize in geriatric medicine is that more treatment does not always mean better treatment.
Sometimes the most useful thing we can do is simplify.
That applies to prescription medications, over-the-counter products, and dietary supplements.
As a lifestyle medicine physician, I also encourage people to look at the bigger picture.
Are they eating a variety of plant foods? Are they getting enough fiber? Are they physically active? Are they sleeping well? Are they managing their chronic medical conditions?
We have substantial evidence supporting fiber-rich dietary patterns for cardiometabolic and gastrointestinal health. We have much less evidence that everyone benefits from taking a daily probiotic or prebiotic supplement.
Before adding another product, I would rather understand what someone is already doing to support their health.
The Bottom Line
The gut microbiome is an exciting area of medical research, and I believe we will continue to learn a great deal about its relationship with aging, inflammation, metabolic health, and cognition.
But we need to distinguish between promising science and proven clinical benefits.
Probiotics are not all the same. Higher bacterial counts do not necessarily mean better results. More strains do not necessarily mean a better product. And probiotics are not appropriate for everyone.
Prebiotics can help support beneficial microorganisms already living in our gut, but not everyone needs a prebiotic supplement, either.
Some products may help in certain circumstances, while others offer little proven benefit and can occasionally cause harm.
For me, this conversation is part of a much broader approach to healthy aging.
I encourage people to focus on the foundations of health, including nutrition, movement, sleep, social connection, and managing chronic medical conditions.
Those foundations are central to the HEALTH Framework I teach through GeriAcademy.
And remember, supporting your gut microbiome does not necessarily require buying a bottle of bacteria.
Sometimes it begins with what is already on your plate.
A final reminder: Before starting a probiotic or prebiotic supplement, particularly if you are an older adult with chronic medical conditions, speak with your physician or another qualified healthcare professional. Even supplements sold without a prescription can carry risks.
Medical Disclaimer
This article is intended for educational and informational purposes only. It is not medical advice and should not be used to diagnose, treat, or prevent any medical condition.
The information presented is not a substitute for individualized medical evaluation or treatment by your physician or another qualified healthcare professional.
Probiotic and prebiotic supplements may not be appropriate for everyone. Probiotics can cause adverse effects, including rare but potentially serious infections, particularly in people with weakened immune systems or certain medical conditions. Prebiotics can also worsen gastrointestinal symptoms in some individuals.
Always speak with your physician before starting a probiotic or prebiotic supplement, especially if you have chronic medical conditions, take prescription medications, have a weakened immune system, or have recently been hospitalized.
Do not delay medical evaluation of persistent or concerning symptoms because of information presented in this article.
The mention of specific probiotic brands is for educational purposes only and does not constitute an endorsement or recommendation.
References and Further Reading
National Institutes of Health, Office of Dietary Supplements. Probiotics: Fact Sheet for Health Professionals.https://ods.od.nih.gov/factsheets/Probiotics-HealthProfessional/
National Institutes of Health, Office of Dietary Supplements. Probiotics: Consumer Fact Sheet.https://ods.od.nih.gov/factsheets/Probiotics-Consumer/
Su GL, et al. AGA Clinical Practice Guidelines on the Role of Probiotics in the Management of Gastrointestinal Disorders. Gastroenterology. 2020.https://doi.org/10.1053/j.gastro.2020.05.059
Hill C, et al. Expert Consensus Document: The International Scientific Association for Probiotics and Prebiotics Consensus Statement on the Scope and Appropriate Use of the Term Probiotic. Nature Reviews Gastroenterology & Hepatology. 2014.https://doi.org/10.1038/nrgastro.2014.66
Gibson GR, et al. Expert Consensus Document: The International Scientific Association for Probiotics and Prebiotics Consensus Statement on the Definition and Scope of Prebiotics. Nature Reviews Gastroenterology & Hepatology. 2017.https://doi.org/10.1038/nrgastro.2017.75
Swanson KS, et al. The International Scientific Association for Probiotics and Prebiotics Consensus Statement on the Definition and Scope of Synbiotics. Nature Reviews Gastroenterology & Hepatology. 2020.https://doi.org/10.1038/s41575-020-0344-2
National Center for Complementary and Integrative Health. Probiotics: Usefulness and Safety.https://www.nccih.nih.gov/health/probiotics-usefulness-and-safety
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