Israeli Scientists Question the Benefits of Probiotics

For a long time, it was believed that probiotics, which are live micro-cultures – bacteria and yeasts – found in some foods and included in dietary supplements, improve gut function and prevent the development of various diseases. They are among the most consumed dietary supplements in the world – more than 60% of doctors in last year's survey admitted that they prescribe them to their patients.

A recently published study by Israeli scientists on the benefits of probiotics, which have not actually been proven by medicine, questions the widespread idea that regular intake of "good" bacteria may have any health benefits and indicates that under certain conditions they may even cause harm. In two different studies, the results of which were published in the latest issue of the scientific journal Cell, scientists from the Weizmann Institute showed that the intake of 11 of the most common strains of probiotics, tested on mice and humans, was in most cases "slightly more than useless".

The First Study

The experiment involved 25 healthy volunteers who were divided into two groups: one group was given a preparation containing 11 strains of probiotics for four weeks, while the other received a placebo. Before the study began, each participant underwent an endoscopy of the upper gastrointestinal tract and a colonoscopy; three weeks later, they underwent these examinations again to determine the impact of the live micro-cultures and placebo on their bodies.

During the study, the team of scientists led by Professor Eran Elinav from the Department of Immunology and Professor Eran Segal from the Department of Computer Science and Applied Mathematics attempted to determine whether the "good" bacteria would establish colonies in the gut and whether any changes would occur in the activity of the microbiome – the collection of tens of trillions of microorganisms known as gut flora.

According to a press release, they found that in each specific case, probiotics colonized the gut differently: in some people, they left almost immediately, providing no benefit, while in others they established colonies and took hold.

"The results we obtained suggest that the same 'good' bacteria cannot be universal and suitable for everyone, – says Professor Elinav. – Therefore, probiotics should be selected individually for each person, taking into account the characteristics of the body and its needs at a given moment. And we even figured out how to conduct this personalized selection."

According to the scientists, based on the results of the study, they metaphorically divided the volunteers participating in the experiment into two groups: "persisters," whose gut accepted the probiotic micro-cultures, and "resisters," whose bodies expelled the received bacteria. They note that it is possible to determine whether a person is a "persister" or a "resister" by examining their baseline microbiome and gene expression profile. The former showed changes in the composition of gut flora and gene expression profile after taking probiotic preparations, while the latter did not.

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The Second Study: Probiotics After Antibiotics

In the second study, Israeli scientists examined the effect of probiotics after a course of antibiotic treatment. They administered broad-spectrum antibiotics to 21 volunteers, who underwent endoscopy of the upper gastrointestinal tract and colonoscopy at the end of the experiment to track changes that occurred in the gut and its microbiome.

The volunteers were divided into three groups. One group was simply observed, allowing their microbiome to recover on its own, another group took a mixture of 11 strains of "good" bacteria for a month, and the third group underwent restorative treatment using an autologous fecal microbiota transplant created from their own bacteria, a sample of which was taken from them before the start of the antibiotic course.

The researchers admitted they were surprised to find that in the group taking the probiotic mixture, the colonizing micro-cultures established well in the gut but significantly slowed the recovery of the composition of "good" bacteria in the gut microbiome. In contrast, those treated with fecal transplantation had their gut microbiome restored within a few days.

"The results of our study revealed a new and potentially dangerous side effect of taking probiotics after a course of antibiotic treatment, which may have long-term consequences. Conversely, personalized treatment involving replenishing the gut microbiome with its own bacteria will not have the negative consequences associated with medications. Contrary to the common belief that probiotic preparations are harmless and beneficial for absolutely everyone, we have proven that their prescription must be strictly individual," concluded Professor Segal.

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