One of the first-ever human studies on probiotics was conducted in 1922, and since then, probiotic research has exploded. The implications for human health, however, are still uncertain.
To explore potential benefits and how far they extend, researchers at the University College Roosevelt in the Netherlands undertook an analysis of all the studies on probiotics registered between 2005 and 2024 in ClinicalTrials.gov.
Speaking at the congress, Ger Rijkers, professor emeritus in biomedical and life sciences at the university, explained the findings.
Conducting the research
Using the search term ‘probiotics’, the researchers identified 2,496 potential studies for their review. After excluding research that did not meet the inclusion criteria, 504 publications were read and reviewed.
Guidance from EFSA was used to decipher clinical outcome parameters, with studies assessing for changes in stool frequency or type, according to the Bristol Stool Chart, included in the review.
In total, 405 different outcome parameters were identified, with most of the studies focusing on improving gastrointestinal symptoms (n=148). This was followed by studies on infants (n=49) and metabolic disorders (n=40).
In addition to the pre-defined clinical outcomes, the studies had to show a significant improvement in quality of life for the patient.
“We did this because the most recent insights say we must determine a ‘minimal clinically important difference’,” Professor Rijkers explained.
From the patient’s perspective, this is defined as a meaningful change in quality of life (e.g. a reduction in symptoms), whereas, for physicians, this could indicate a beneficial change in treatment or the prognosis of the disease.
Vast majority of probiotic studies show clinical benefits
Of the included studies, 52% reported a positive primary outcome, 20% had a positive secondary outcome, and 26% saw no change. A very small number reported a negative effect (2%).
“This means an amazing 72% of the reported clinical studies for probiotics have a positive effect both clinically and for quality of life measures,” Professor Rijkers said.
Studies analyzing metabolic outcomes had the most positive effect overall at 87%, followed by gastrointestinal outcomes at 68%.
The researchers then compared studies analyzing single-strain probiotics and multi-strain probiotics. Perhaps surprisingly, they found no significant differences.
“There is absolutely no difference in the clinical effect in both cases,” Professor Rijkers said. “If you add another strain, it doesn’t make it better […] So this is food for thought for future design of clinical studies.”
Finally, the researchers analyzed whether there have been any improvements in the success rates of clinical studies with probiotics over time.
They found that 75% of studies between 2013 and 2021 reported a positive outcome, which is significantly higher than studies from 2005 to 2012 at 64%.
This suggests that probiotics are potentially becoming more efficacious and providing more benefits for consumers as the research landscape evolves.
