Many of us are drawn to health claims about probiotics’ promise of improved gut health, stronger immunity, and even clearer skin. You’ve likely seen them everywhere, on yoghurt containers, in dietary supplement aisles, and even in skincare products. But as you contemplate whether to add that kombucha or probiotic supplement to your cart, you might wonder: do these products actually work? Are they worth the investment?

Understanding what probiotics are, when they’re beneficial, and who should take them can feel overwhelming amid marketing claims and conflicting advice. Today, we’re exploring the scientific evidence behind probiotics: what they are, how they function in your body, and what research actually tells us about their effectiveness.

What Are Probiotics?

Simply put, probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit on to you. These beneficial bacteria and yeasts are similar to the microorganisms already living in your gut, which make up your gut microbiome.

Your digestive tract contains trillions of bacteria, both beneficial and harmful microbes. The beneficial bacteria help digest food, destroy disease-causing cells, and produce vitamins. Should this delicate balance be disrupted by poor diet, stress, illness, or antibiotics—it could lead to digestive issues, immune problems, and other health concerns. Antibiotics can disrupt this balance, leading to conditions such as antibiotic-associated diarrhoea, where probiotics have been shown to help restore gut health.

Probiotics aim to restore this balance by introducing beneficial microorganisms into your gut. They’re commonly found in fermented foods like yoghurt with active cultures, kimchi, and sauerkraut, but are also widely available as dietary supplements in multiple forms, from oral supplements to powders and liquids.

How Do Probiotics Work?

Probiotics exert their health benefits through several mechanisms, which vary depending on the specific probiotic strains and species. Some common ways probiotics influence your health include:

1. Maintaining your gut barrier integrity: Probiotics can strengthen the intestinal wall, preventing harmful substances from crossing into the bloodstream.

2. Reducing activity of harmful microorganisms: They either compete with harmful bacteria for nutrients or provide antimicrobial effects to reduce the growth of potentially harmful bacteria.

3. Enhancing the immune response: Probiotics can influence your body's immune system, potentially reducing inflammation and improving immune function.

4. Aiding in digestion: Certain probiotics help break down food components and synthesise vitamins.

5. Producing beneficial substances: Many probiotics produce short-chain fatty acids that support gut health and function. Short-chain fatty acids are beneficial compounds produced during digestion that nourish and support your gut lining. 

Gut Health and the Microbiome

The gut microbiome is a bustling ecosystem of trillions of microorganisms residing in your gastrointestinal tract. This complex community plays a pivotal role in maintaining your overall health, influencing everything from digestion and immune function to the production of essential vitamins. When the balance of these gut microbes is disrupted—a condition known as dysbiosis—it can lead to various health issues, including irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), and even obesity.

Probiotics come into play by introducing beneficial microbes into your gut, helping to restore balance and support a healthy microbiome. A well-balanced microbiome is crucial for a robust immune system and disease prevention. By maintaining a healthy gut, you can enhance your overall well-being and reduce the risk of various health conditions.

Probiotics and Prebiotics

Probiotics are live microorganisms that, when taken in adequate amounts, confer a health benefit to the host. These beneficial microbes can be found in various forms, including dietary supplements and fermented foods like yogurt, kefir, and sauerkraut. On the other hand, prebiotics are non-digestible fibers that serve as food for these beneficial microbes, promoting their growth and activity in the gut.

When combined, probiotics and prebiotics create synbiotics, which enhance the health benefits of both. This synergistic effect can lead to improved digestion, better immune function, and overall enhanced gut health. Incorporating both probiotics and prebiotics into your diet through foods and supplements can provide a powerful boost to your gut microbiome.

The Scientific Evidence: Where Probiotics Show Promise

With research into the gut microbiome still in its infancy, increasing evidence suggests that both commercial and clinical use of probiotics is outpacing the science. Despite their widespread popularity, the scientific evidence for probiotics varies significantly depending on the specific condition and probiotic organism type. Here's what systematic reviews and meta-analyses tell us about some common uses:

Antibiotic-Associated Diarrhoea

One of the most well-established benefits of probiotics is preventing diarrhoea caused by antibiotics. Antibiotics can disrupt your gut microbiota by killing both harmful and beneficial bacteria, often leading to diarrhoea in up to 30% of patients.

Multiple systematic reviews and meta-analyses have shown that certain probiotics, particularly Lactobacillus rhamnosus GG and Saccharomyces boulardii, can reduce the risk of antibiotic-associated diarrhoea. For the best results, research suggests starting probiotics within two days of beginning antibiotics.

However, taking probiotics after antibiotic treatment is an increasingly common practice that may require more careful consideration. Research investigating the recovery of the gut microbiota after antibiotic treatment found that probiotics might hinder rather than aid this process.

Irritable Bowel Syndrome (IBS)

IBS affects approximately 10-15% of the global population, causing symptoms like abdominal pain, bloating, and altered bowel habits. Research indicates that in people with IBS, populations of beneficial bacteria like Lactobacillus and Bifidobacterium decrease, while inflammatory bacterial species increase.

Probiotics have been found to reduce IBS symptoms, albeit modestly and without a consistent positive effect on quality of life. A systematics reviews found that multiple probiotic strains appear to be more effective than single-strain products; effects vary by individual, and finding the right probiotic might require some trial and error.

It takes at least 4 weeks to experience changes to your gut microbes, so one could try probiotic supplementation for up to 12 weeks and discontinue if there is no improvement in symptoms. Different probiotic strains may be more effective for specific IBS symptoms. Some might help with bloating, while others may better address abdominal pain.

Inflammatory Bowel Disease (IBD)

For people with inflammatory bowel diseases (IBD) such as Ulcerative Colitis or Crohn’s disease, the evidence for probiotics is mixed.

Some research suggests that certain probiotic treatments, particularly VSL#3 (a multi-strain preparation), may help maintain remission in Ulcerative Colitis when used alongside conventional treatments. However, there is insufficient evidence to support their use in Crohn’s disease. Randomised controlled trials continue to explore this area, and guidelines from clinical infectious diseases specialists generally recommend probiotics only be used as complementary and integrative health approaches rather than as primary treatment.

Infectious Diarrhoea

While some meta-analyses have suggested that probiotics might help reduce the duration of infectious diarrhoea, particularly in children, clinical trials have cast doubt on this conclusion. These trials used probiotics available over the counter and showed no significant difference from placebo in the duration of diarrhoea and vomiting, suggesting that the benefits of probiotics for infectious diarrhoea may be less substantial than previously thought.

Where Evidence Is Limited or Mixed

Despite popular health claims, scientific evidence for probiotics is limited or inconsistent for many conditions:

Weight Management and Obesity

There is limited evidence of probiotics' impact on body weight and obesity as their effects are dependent on several factors, including the probiotic strain, dose, and duration, as well as your age, sex, and body weight. While some animal studies suggest that certain strains of Lactobacillus and Bifidobacterium might influence weight regulation, human clinical trials show inconsistent results.

Cholesterol Levels

There is insufficient evidence to demonstrate the role of probiotics in binding to cholesterol in the intestine or producing compounds that regulate cholesterol metabolism. Some small studies suggest that Lactobacillus acidophilus and certain other strains might modestly reduce total and LDL cholesterol levels, but larger, well-designed trials are needed to confirm these effects.

Mental Health and the Gut-Brain Axis

The connection between gut health and mental wellbeing has sparked interestin using probiotics for conditions like anxiety and depression. While preliminary research is promising, high-quality evidence from clinical trials is still lacking, and more research is needed before specific recommendations can be made.

Urinary Tract Infections

Some evidence suggests that certain Lactobacillus strains might help prevent recurrent urinary tract infections in women, but the evidence is not strong enough for most medical societies to recommend their routine use for this purpose.

Choosing the Right Probiotic

If you're considering probiotics, keep these factors in mind:

1. Strain Specificity

The effects of probiotics are strain-specific. Different strains, even within the same species like Lactobacillus casei or Lactobacillus acidophilus, can have vastly different effects on human health. Look for products that list the complete scientific names (genus, species, and strain) of the probiotics they contain.

For example, instead of just "Lactobacillus," look for something like "Lactobacillus rhamnosus GG" or "Bifidobacterium lactis BB-12".

2. Quality and Viability

Probiotics must be alive to provide health benefits. Look for probiotic products that guarantee the number of viable microorganisms through the end of the product's shelf life, not just at the time of manufacture. Some products may require refrigeration to maintain viability of the live bacteria.

3. Potential Risks

For most healthy people, probiotics are generally safe with few side effects beyond mild digestive symptoms like upset stomach or flatulence. However, people with compromised immune systems, critical illnesses, or certain medical conditions should consult a healthcare provider before using probiotics.

The ubiquity of probiotic products might suggest they are harmless, but some safety concerns have been raised, including the risk of contamination, possibility of bacteraemia (particularly in immunocompromised individuals), and even potentially fatal disease in vulnerable populations. Adding to these concerns, clinical trials of probiotics have not consistently reported safety outcomes.

Food vs. Probiotic Supplements

While oral probiotic supplements are convenient, probiotic-rich foods provide not only beneficial microorganisms but also additional nutrients and dietary fibre. Foods like yoghurt with live cultures, kefir, sauerkraut, kimchi, and other fermented foods can be valuable additions to a balanced diet.

Commercially available probiotic 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 gut microbiota.

Regulation and Safety

Probiotics are regulated by the FDA as dietary supplements, which means they do not require the same rigorous proof of safety and efficacy as medications. However, the FDA mandates that probiotic products be labeled accurately, providing clear information about their ingredients and potential health benefits.

For most people, probiotics are generally safe and come with few side effects, such as mild digestive symptoms like upset stomach, diarrhea, gas, and bloating. However, individuals with compromised immune systems or serious health conditions should consult a healthcare provider before taking probiotic supplements. While probiotics offer numerous health benefits, it’s essential to choose high-quality products and use them appropriately.

Fermented Foods and Probiotics

What are Fermented Foods?

Fermented foods are those that have undergone a natural process of breakdown by microorganisms, such as bacteria or yeast. This fermentation process not only preserves the food but also creates beneficial compounds, including probiotics. Examples of fermented foods include yogurt, kefir, sauerkraut, kimchi, and kombucha. These foods have been consumed for centuries and are rich sources of probiotics and other health-promoting compounds.

Probiotics in Fermented Foods

Fermented foods contain a variety of probiotic strains, such as Lactobacillus and Bifidobacterium. The probiotic content can vary depending on the type of food, the fermentation process, and storage conditions. Regular consumption of fermented foods can provide a range of health benefits, including improved digestion, enhanced immune function, and better mental health. By supporting the growth of beneficial microbes in the gut, fermented foods can promote overall health and well-being. Plus, they are a delicious and convenient way to incorporate probiotics into your diet.

By understanding the science behind probiotics and making informed choices, you can harness the potential health benefits.

The Science Is Still Evolving

While the logic behind probiotics might seem sound, we still have a long way to go before understanding the complexity of the gut microbiome and the effects—both good and bad—that probiotics might have. All individuals have a unique gut microbiota, and the effects of different bacteria on different people are likely to be highly variable.

In one study, they found that probiotic colonisation occurred in highly individualised patterns, with some people's gastrointestinal tracts rejecting probiotics and others accepting them. This suggests that many individuals taking probiotic supplements might not be getting any benefit, and that probiotic use might even need to be personalised for optimal benefits.

The Bottom Line

Probiotics offer promising benefits for specific gastrointestinal disorders, particularly antibiotic-associated diarrhoea and certain symptoms of IBS. However, evidence from clinical trials is mixed and often of low quality, but findings from studies suggest that probiotics can provide benefits in some specific contexts.

If you're considering taking probiotics for a specific health condition, consult with a healthcare professional who specialises in digestive health to help you navigate the complex world of probiotic research.

Remember that probiotics work best as part of a holistic approach to health. A diet rich in diverse plant foods, adequate fibre, regular physical activity, sufficient sleep, and stress management all contribute to a healthy gut microbiome and overall wellbeing. These microorganisms thrive on different nutrients, particularly fibre and plant compounds found in fruits, vegetables, wholegrains, nuts, and seeds. By consuming a varied diet rich in these nutrients, you're naturally cultivating a diverse and resilient gut community, which may offer more consistent benefits than probiotic supplements alone.

Think of probiotics not as a magic bullet, but as one tool in your wellness toolkit—potentially beneficial in the right circumstances, but most effective when combined with other healthy lifestyle practices. Those looking to support their gut microbiota might be better served by consuming a healthy, varied diet while rigorous clinical trials continue to examine how probiotics effect human health

References

1. International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nat Rev Gastroenterol Hepatol. 2014.

2. Suez J, et al. Post-antibiotic gut mucosal microbiome reconstitution is impaired by probiotics and improved by autologous FMT. Cell. 2018.

3. Ford AC, et al. Efficacy of prebiotics, probiotics, and synbiotics in irritable bowel syndrome: systematic review and meta-analysis. Am J Gastroenterol. 2014.

4. Freedman SB, et al. Multicenter Trial of a Combination Probiotic for Children with Gastroenteritis. N Engl J Med. 2018.

5. American Gastroenterological Association. Clinical Practice Guidelines on the Role of Probiotics in the Management of Gastrointestinal Disorders. Gastroenterology. 2020.

6. Zmora N, et al. Personalized Gut Mucosal Colonization Resistance to Empiric Probiotics Is Associated with Unique Host and Microbiome Features. Cell. 2018;174(6):1388-1405.