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Probiotic Supplements - The Reality of Preventive Supplementation

A Review of the Paper "A Review of Probiotic Supplementation in Healthy Adults: Helpful or Hype?

02/01/2019 - Product Review Newsletter #322

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Virtually since its inception, Probiotic Select has been one of our best-selling products.  While many purchasers employ Probiotic Selectas part of an interventive program to address a clinical concern, which is, more often than not, related to GI dysfunction, there is no question that many if not most purchasers of Probiotic Select use the product as a preventive measure to avoid dysfunction.  While there is no question that a massive volume of information in print and on the Internet advocates preventive use of probiotic supplements, does published research support this common practice?  Of course, one easy answer to this question relates to the use of probiotic supplements to reduce or prevent GI-related side effects from oral antibiotics, which is well supported by several studies.  However, beyond that, is there any real benefit for basically healthy individuals who have no acute health concerns to ingest probiotic supplements for sometimes months and years, as is often the case?

As you will see, the recently published paper "A review of probiotic supplementation in healthy adults: helpful or hype?" by Khalesi et al (Khalesi S et al. Eur J Clin Nutr, Vol. 73, pp. 24-37, 2019) suggests that the answer is yes, at least some of the time.  Interestingly though, as will be highlighted, the benefits generally do not occur for the reason most people believe.  More on that later.


The first quote I would like to feature from this paper points out that, even though much published research exists on the benefits of probiotic supplementation with ailing populations, very little exists on the use of probiotic supplements with healthy individuals:

"While research has demonstrated positive effects of probiotic consumption on several health outcomes, the majority of the published literature is in populations with underlying pathologies.  Evidence supporting the health-promoting effects of probiotics in healthy adults is limited and less consistent."

To ascertain this aspect of probiotic use, Khalesi et al conducted a review of the literature using the following protocol:

"Studies were included if they (1) were experimental trials, (2) included adults, aged 18 years and older, (3) used live bacteria (probiotics), (4) included healthy adults, and (5) had accessible full-text publications in English.  Healthy adults were defined as individuals with no reported status of chronic or acute diseases, including cardiovascular disease (CVD), obesity (body mass index (BMI) ≥ 30 kg/m2), liver disease, cancer, psychological disorder, etc.  Adults who reported having symptoms consistent with the common cold, who were overweight (BMI 25-29.9 kg/m2) or smokers, were not included.  Studies were excluded if probiotic treatment was mixed with other ingredients, or if pregnant women or both healthy and unhealthy adults were included as participants in one group."

Relevant studies published between 1990 and August 2017 were considered.  In all, 45 studies were included in the Khalesi et al review. 

The impact of probiotic supplements on gut microflora populations

In terms of the impact of probiotic supplements in healthy populations, it is my guess that the authors began here as this is, as you will see, where the biggest misconceptions reside in terms of why most people ingest probiotic supplements preventively.  As you are undoubtedly aware, it is the opinion of many, if not most, in both the healthcare community and the population at large that quality probiotic supplements will make permanent, beneficial changes to resident microflora.  In partial agreement, Khalesi et al state:

"Changes in the concentration and composition of intestinal microorganisms would suggest that probiotics are effective, at least in terms of colonization."

However, contrary to the belief of many, as I mentioned, the authors also reported the following:

"It also appears that changes in the gut microbiota of healthy adults following probiotic supplementation are temporary and return to pre-treatment levels within 1-3 weeks once supplementation has ceased."

Next, the authors discuss another popular misconception about the need for probiotic supplements to establish gut colonization to be effective.  This is also not true:

"...colonization may not necessarily be required for changes in the gut microbiota.  The passage of probiotic bacteria (e.g., bifidobacterial) itself through the gut may be sufficient to reduce colonies of pathogenic bacteria by reducing their adhesion and competitive nature."

Interestingly, what can make somewhat permanent changes to resident gut microflora is what is often included in probiotic supplements, including Probiotic Select - prebiotics:

"Evidence suggests that prebiotic consumption can improve the fecal count of beneficial bacteria (especially bifidobacteria) and maintain gut health."

Nevertheless, when dysbiosis is present, as with diarrhea, prebiotics alone are not enough:

"When gut microbiota dysbiosis exists (e.g., diarrhea), prebiotics alone may not be able to return gut microbiota to its equilibrium."

In this situation where dysfunction exists, as suggested above, probiotic supplements demonstrate legitimate benefit:

"...probiotics have proven beneficial effects when dysbiosis exists."

Before leaving this discussion on the controversy about the impact of probiotic supplements on resident microflora, I would like to present one additional quote that addresses the sometimes passionate assertion by supplement companies, clinicians, and the general public that organisms in probiotic supplements must enter the distal small intestine and large intestine in a viable state to be effective.  While this is certainly preferred, is it absolutely necessary in order for probiotic supplements to demonstrate benefit?  Khalesi et al state:

"Although viability is acknowledged as a prerequisite for the health benefits of probiotics, few interventions have reported the viability of probiotics during the period of supplementation.  Evidence suggests that non-viable probiotic strains may also confer some positive health outcomes..."

Please note again the preceding quote.  While it makes sense that viable organisms will be beneficial, very few studies on the clinical impact of probiotic supplements, even though they reported positive outcomes, actually investigated whether the organisms in the supplements were indeed living.  It was just assumed they were living based on the positive outcome.  In fact, as suggested in the above quote, it is very possible that positive results were obtained by non-viable organisms.  What does this reality mean in terms of the Moss Nutrition product, Probiotic Select?   Moss Nutrition takes every possible measure to maintain optimal organism viability in Probiotic Select.  However, there is no question that minor decreases in viability may occasionally occur, most often due to increases in temperature during shipping in the summertime.  Does such an occurrence render the product "dead" and "worthless" as believed by many?  As suggested by Khalesi et al, research points out that this belief has no scientific basis.

Clinical impact of probiotic supplements in healthy populations - immune support

A common reason probiotic supplements are ingested preventively is to support immune function.  Does clinical research support this reasoning?  Published research on the subject examined by Khalesi et al considered two clinical entities - influenza and the common cold.  Concerning influenza, the research was conflicted:

"...the effect of probiotic supplementation on immune responses against influenza infection in heathy adults is less consistent."

In contrast, research on probiotics and the common cold are encouraging:

"Overall, it appears that probiotic supplementation in healthy adults can improve immune function and the immune response to common cold infections."

Clinical impact of probiotic supplements in healthy populations - lipid profiles and cardiovascular disease risk

Some have suggested that probiotic supplements can help optimize LDL, HDL, and triglyceride levels.  According to Khalesi et al, this is not true:

"There is insufficient evidence to support the role of probiotics to improve blood lipid profile."

Clinical impact of probiotic supplements in healthy populations - GI discomfort

As noted by the authors, it is well recognized that probiotic supplements can be very beneficial for the optimization of GI function in ailing populations:

"Benefits of probiotic supplementation in the treatment and management of many types of diarrhea and constipation have been reported in unhealthy populations."

However, what about the basically healthy individual who experiences occasional GI dysfunction due to stressful situations or short-term dietary indiscretions?  Research does demonstrate that probiotic supplements can also be helpful in these situations:

"Overall, it appears that probiotic supplementation may be effective at improving stool consistency, bowel movement, and reducing irritation caused by abdominal bloating."

Ironically, in contrast to what is seen in unhealthy, chronically ailing patients, i.e., IBS, in healthy populations no one really knows what the mechanism is for the positive effects of probiotic supplements:

"The relevant mechanisms of probiotics in this action remain unclear.  However, fermentation of non-digestible carbohydrates and production of short-chain fatty acids (SCFA) and carbon dioxide, removal of other intestinal gases, and the anti-inflammatory effect of probiotics have been suggested as possible mechanisms."

Clinical impact of probiotic supplements in healthy populations - female reproductive system health

There has been the suggestion over the years that probiotic supplementation via vaginal suppositories or even oral administration can help optimize vaginal health.  Khalesi et al begin their discussion on this subject by pointing out the following:

"From birth until after puberty, lactobacilli are the predominant microorganisms populating the vaginal microbial environment.  However, after puberty the microbial environment changes due to menstruation, hormonal changes, intercourse, infections, and hygiene.  This often results in a vaginal environment that is not predominant in lactobacilli bacteria for the majority of women, increasing susceptibility to urogenital infections such as urinary tract infection and bacterial vaginosis."

Can probiotic supplementation demonstrate benefit?  The authors point out:

"Four studies (five trials, one study had two arms) have examined the effects of oral supplementation or vaginal suppositories with lactobacilli as a means of improving the vaginal environment.  Among these, four trials have suggested there was a significant increase in the level of vaginal lactobacilli.  Supplementation with L. acidophilus, L. rhamnosus, or L. fermentum increased vaginal lactobacilli levels in healthy women.  The increase in vaginal lactobacilli populations seems to prevent and reduce the incidence of vaginal infections in otherwise healthy adult women."

Clinical impact of probiotic supplements in healthy populations - psychological health

As noted by Khalesi et al, psychological stress can have a profound impact on gut microflora:

"Psychological distress can reduce the number and diversity of intestinal microorganisms by changing intestinal transit time, acidity, mucus secretion, stress hormones, and immune response."

With this in mind, does research suggest that probiotic supplements might be helpful with psychological symptoms in healthy adults?  The authors comment:

"Collectively, evidence from these studies suggests that probiotic supplementation may improve psychological symptoms in healthy adults."

Some final, big picture thoughts

I would like to finish this review by pointing out two key points made by Khalesi et al:

Preventively, probiotic supplementation in healthy populations needs to be taken continuously to demonstrate benefit.

"...supplementation with probiotics may need to be an ongoing process in order to maintain gut microbiota changes in healthy adults.  Gut microbiota is sensitive to multiple factors, such as lifestyle, aging, and disease.  Even in apparently healthy individuals, changes in diet quality and alcohol intake can significantly affect gut symbiosis.  A diet poor in fruit and vegetable intake (as a good source of prebiotics) may not provide the food required for probiotic survival and maintenance.  This may explain the constant need for probiotic food and supplements to maintain gut symbiosis and health."

Probiotic supplementation in healthy populations can have a significant impact in optimizing immune function in relation to upper respiratory infections

"The current review also suggests that probiotic consumption in healthy adults may improve immune function, particularly in response to common upper respiratory infections; reducing their incidence and/or symptom severity.  This is particularly important since improved immune function via probiotics may reduce the antibiotic needs in infections, thus reducing the risk of antibiotic resistance - one of the greatest global threats of the present decade.  Probiotics may enhance the immune response by activating T lymphocyte cells, increasing NK cell activity and anti-inflammatory cytokines (e.g., IL-12 and IL-14).  These findings are in agreement with a recent meta-analysis (including both healthy and unhealthy populations) indicating that probiotic consumption may have a protective effect against the common cold."

Unfortunately, along with the tremendous increase in interest and usage of probiotics among both the health care community and the general public has come some major misconceptions about their properties, their clinical effects, and the mechanisms underlying these clinical effects.  I hope you will agree that this very timely and important paper goes a long way to help everyone, from manufacturers like Moss Nutrition to clinicians and end users, gain a better understanding about the reality of the strengths and limitations of probiotic supplements such as Probiotic Select