Probiotics: But not useful?

Studies question the efficacy of probiotic agents

Probiotic foods and dietary supplements are designed to promote healthy intestinal flora - but their benefits are controversial. © M_a_y_a / istock
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Because of beneficial bacteria: Probiotics may not be as healthy as you thought. No two studies suggest that the benefits of such remedies could be very limited. Accordingly, the microorganisms contained in the products do not settle in the gut of any human successfully. The negative effects of taking antibiotics do not seem to be able to compensate for probiotic drugs - on the contrary, they may even be counterproductive.

Whether as yogurt or in the form of capsules and powder: Probiotics enjoy great popularity. The bacterial strains contained in them should settle in the digestive tract, provide for a healthy intestinal flora and so can prevent a variety of complaints. But how useful is the intake of such funds really?

"Scientific data on this are scarce and sometimes very contradictory, " says Eran Elinav from the Weizmann Institute of Science in Rehovot, Israel. The immunologist and his colleagues have now taken a closer look at the effectiveness of probiotics. They wanted to know: Do the microorganisms from yoghurt and co get into the intestine - and if so, what influence do they have?

Successfully settled?

For their study, the scientists performed colonoscopy on 15 healthy volunteers, taking samples to determine the composition of the microbiome. The participants were then divided into two groups: one was given a conventional probiotic with eleven different bacterial strains, the other a placebo. Over a period of two months, the researchers then observed what happened through the intake in the gastrointestinal tract.

It turned out that while the microorganisms successfully settled in some subjects, this did not work for others at all. For whom the probiotics were effective and who did not, it was even possible to predict, as the team noted: The success was dependent on the original composition of the microbiome as well as certain gene expression patterns in the gastrointestinal tract. display

In the stool, but not in the gut

In addition, the investigations revealed that the bacteria found inside the body did not always agree with what was found in the participants' stool: "We have been able to detect the probiotics in the stool in all the test persons, but only in some of the intestines there where they go, "says Elinav's colleague Eran Segal.

This is an important finding because studies to date have often used stool samples to study the microbiome instead of measuring the bacterial community directly in the gastrointestinal tract. According to the researchers, this means that some of the results of recent years regarding the efficacy of probiotics could be misleading.

No universal benefit

"Our work shows that the benefits of probiotic food and nutritional supplements are not as universal as thought, " says Segal. But that's not all: in a second study, the scientists found that probiotics are more than ineffective under certain circumstances they can even be counterproductive.

In this study, researchers looked into the question of what the use of probiotic drugs after taking antibiotics brings. This measure should help to restore the disturbed by the drugs intestinal flora faster. But does that work too? The team initially administered 21 antibiotics to 21 subjects and then randomly assigned them to one of three groups. Part of the participants were not treated at all, part of them received the probiotic from the first study and another part of the body's own bacteria in the form of a stool transplant.

Negative effect

Surprisingly, it turned out that after the antibiotic had eliminated all of the body's own bacteria in the intestine, the microorganisms from the probiotic settled successfully in all volunteers. These foreign bacteria, however, apparently prevented the composition of the intestinal flora from returning to its normal state, even months later.

The subjects who had received the stool transplantation were quite different: The intestinal flora recovered significantly faster with them within a few days and returned to normal, as the researchers report. "According to the current dogma, probiotics are harmless and useful to everyone. However, our findings point to a potential undesirable side effect that may even have long-term consequences, "says Segal.

"In contrast, treatment with the body's own bacteria could be more useful - a personalized probiotic developed by Mother Nature, " the researcher concludes. (Cell, 2018; doi: 10.1016 / j.cell.2018.08.041 and doi: 10.1016 / j.cell.2018.08.047)

(Cell Press, 07.09.2018 - DAL)