Myths about probiotics debunked

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Written By:

Katie Stone - Naturopath

Medical Reviewer:

Kari Asadorian - BSN, RN

Edited By:

Jamie Hope - Methyl-Life® Founder

Last updated: April 8, 2026

Probiotics don’t have an impact on health

MYTH

Probiotics are clinically defined as “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host”.¹ Numerous clinical studies have demonstrated that probiotics can have significant impact on health when used in specific formats and dosages.

Probiotics are thought to exert beneficial effects by providing protective barriers, enhancing immune responses and clearing pathogens in the gastrointestinal tract. Meta-analyses on the efficacy of probiotics have shown that probiotics are effective in preventing and treating Irritable bowel syndrome (IBS), Helicobacter pylori infection, antibiotic associated diarrhea (AAD), and many common gastrointestinal diseases.²

A 2025 meta-analysis of clinical trials conducted over the past 10 years found that the majority of recent studies supported the efficacy of probiotics in mitigating symptoms of anxiety, depression and cognitive function. Individuals with mild symptoms may experience greater benefits from taking probiotics. A significant body of evidence supports a decrease in inflammatory markers linked to probiotic consumption.³

Yogurt, sauerkraut and kombucha provide enough probiotics/ You can get all the probiotics you need through food

MYTH

Fermented food products such as yogurt, kombucha and kefir are often promoted as containing “probiotic cultures” and “gut-friendly bacteria”. However, while these foods may be a valuable source of vitamins and minerals, the quantity and quality of their probiotic bacteria will not provide that of a probiotic supplement. Claims regarding their probiotic content are rarely backed by clinical evidence.
Fermented foods are largely unregulated and there are no specific standards regarding the viability of their probiotic content or whether they contain probiotics (as per their clinical definition) at all. Recent studies have highlighted that many food products make inaccurate claims about the probiotic microorganisms they contain.^4,5

All probiotics are equal

MYTH

Probiotics may share some characteristics, but different species and strains have different functions. Each of the most commonly used species in supplement products (Lactobacillus, Bifidobacterium, Bacillus, Streptococcus, Enterococcus and yeasts such as Saccharomyces) has unique properties, and specific strains within those species are effective in supporting certain health conditions.

For example, Lactobacillus mainly colonize the oral cavity, gastrointestinal tract and vagina, where they ferment refined sugars to create lactic acid.⁶ Within this genus, the strains Lactobacillus rhamnosus and Lactobacillus acidophilus have demonstrated significant benefits in improving the immune system response and in treating yeast infections.⁷

Bifidobacterium is another genus commonly used in probiotics. It mostly resides in the colon, where it produces short-chain fatty acids (SCFAs), an important energy source for cells.⁸ The strain Bifidobacterium longum has demonstrated efficacy in reducing symptoms of irritable bowel syndrome (IBS).⁹

The species Streptococci reside in the oral cavity and play an important role in dental health.¹⁰

You only need probiotics if you’re taking antibiotics

MYTH

Probiotics are often recommended when taking antibiotics as they help to protect and restore gut flora during and after antibiotic use. Numerous clinical studies show that probiotic supplementation alongside antibiotics prevents many of the disruptions to gut microbial diversity and composition and restores beneficial species, as well as reducing the incidence of antibiotic-associated diarrhea.^11,12

However, the gut microbiome is affected by many factors besides antibiotics, including diet, stress, nutritional deficiencies, smoking, toxins, health conditions, medications and more. Probiotics can help to restore imbalances caused by these stimuli and maintain the composition of the microbiome, which contributes to overall wellbeing.

All probiotics need to be refrigerated

MYTH

Some probiotics do require refrigeration to maintain their viability. However, many species are shelf-stable and only need to be kept in cool, dry conditions (under 25 degrees Celsius, as specified by the manufacturer on the label).

The body will get used to probiotics and they will no longer work

MYTH

Probiotics are live bacteria, so they are only able to function temporarily. When ingested, they travel through the digestive system, supporting other bacteria living in the gut. A 2023 study found that Lactobacillus and Bifidobacterium were found in feces while being taken as supplements and for a short period after the supplementation ended.¹³ They are unable to provide permanent effects, which is why consistent supplementation may be necessary.

As long as the digestive system is exposed to the harmful effects of poor diet (processed food, sugar, trans fats), stress, alcohol, medications and other lifestyle factors, it will need the support of probiotic supplementation.

The more billions, the better

MYTH

Probiotic bacteria are only effective if they are live and active. High numbers of probiotic bacteria can include both live and dead and damaged microorganisms. Even if a product claims to contain 150 billion bacteria, these are unlikely to be effective if they are not guaranteed to be live colony-forming units (CFUs).¹⁴

The efficacy of a probiotic is more accurately determined by the diversity of strains it contains, rather than by a high concentration of a single strain. Studies show that a multistrain probiotic - one that contains several strains that work synergistically - provides more effective and more consistent benefits than a single-strain probiotic.¹⁵

An effective probiotic should show evidence that it contains live bacterial strains that have been tested in human clinical trials, and that the bacteria will survive the passage through the gut.

Don’t take probiotics with antibiotics

MYTH

Taking a probiotic with antibiotics is highly recommended. Antibiotics are designed to kill harmful bacteria but can also reduce beneficial gut bacteria. This can lead to dysbiosis (an imbalance of healthy bacteria) along with symptoms such as bloating, reduced immune function and antibiotic-associated bacteria.

Taking a probiotic with an antibiotic can help maintain populations of healthy bacteria in the intestines while supporting the integrity of the gut lining. Probiotics can also “crowd out” potentially harmful bacteria by competing with them for nutrients and preventing them from growing or spreading.

Look for a probiotic product that is clinically proven to survive alongside antibiotics (this will be stated on the label). Research has shown that the strains Saccharomyces boulardii and Bifidobacterium animalis ssp. lactis BB-12® can withstand antibiotic treatment, supporting the balance of healthy bacteria in the gut and reducing the incidence of antibiotic-associated diarrhea.^16,17

The more strains, the better

MYTH

This is not necessarily true, as viability often has greater impact than the number of strains.
Multiple strains can indeed provide greater health benefits, as different species have different properties. However, as mentioned previously, live probiotics are better able to interact with resident bacteria and actively compete with pathogenic bacteria for nutrients and binding sites on the intestinal walls.¹⁸

Look for a probiotic product that contains both multiple strains and a high number of CFU (colony-forming units).

Sourdough is a good probiotic

MYTH

Sourdough bread is not a source of probiotics. Although the starter culture for the bread contains probiotic yeast and bacteria including Lactobacillus brevis, these probiotics do not survive the high temperatures of baking.
However, sourdough may contain some beneficial byproducts created during the fermentation. These are called ‘postbiotics’ and include compounds such as short-chain fatty acids (SCFAs), peptides, amino acids, flavonoids and other nutrients that may support digestion and gut health.¹⁹