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Over the past decade, probiotic dietary supplements have become a multi-million dollar industry, consumed by nearly 4 million adults and prescribed by nearly 60% of health care providers. Yet the scientific community knows little about how they work or not.
But that will probably change thanks to two consecutive studies published Thursday in Cell, which call into question the benefits of highly marketed probiotic products.
"People have been providing a lot of support for probiotics, even though the literature underlying our understanding is very controversial," said Eran Elinav, lead author and immunologist at the Weizmann Institute of Science in Israel. I wanted to know if probiotics such as those you buy at the supermarket colonize the GI tract as they are supposed to do and if these probiotics have an impact on the human host. "
What are probiotics?
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Probiotics are living microorganisms, often marketed and sold in foods (such as yogurt) and dietary supplements. While most people think that bacteria are "bad" (causing disease), many bacteria play a vital role in our survival. Count among them the bacteria that line the digestive tract and help break down and absorb food, thus fighting infections.
Probiotics are designed to mimic and enhance the effects of these "good" bacteria, considered bacteria that can "rebalance" your system. The claims of the probiotic industry range from cold prevention to the treatment of allergic disorders such as atopic dermatitis. As they are marketed as dietary supplements and not as drugs, the US Food and Drug Administration (FDA) has never approved probiotics for the prevention or treatment of health problems.
Based on these new studies, the path to health claims seems more rock
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While the vast majority of previous studies on probiotics relied on stool analysis to get an idea of the individual's intestinal microbiome, Elinav's research team examined, with an endoscope, the bacteria present. in the colon even in mice and humans.
After 25 healthy volunteers consumed a generic probiotic containing 11 strains of "good" bacteria, they all contained probiotic bacteria in the stool, which the research team was waiting for. But when doctors performed endoscopy to evaluate their intestines, they found that probiotics had actually been "blocked" only in a few people.
"Although all of our volunteers consuming probiotics showed probiotics in their stool, only some of them showed them in their intestines, where they should be," said Eran Segal, a computer biologist at the University of Ottawa. Weizmann Institute. .
If probiotics are not in the colon, it's hard to pretend that they are doing good.
One of the most common uses of probiotics is to fight diarrhea that sometimes occurs after the use of antibiotics. Antibiotics kill the "bad" bacteria that cause the disease, but in the process, many "good" colon bacteria are also sacrificed – hence diarrhea and poor absorption of key nutrients from foods. That's why some doctors ask their patients to take probiotics with a series of antibiotics or right after, to prevent the complete loss of "good bacteria". These providers believe that the use of probiotics in healthy adults is not always effective. at least relatively risk free.
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The researchers asked volunteers to complete a course of broad-spectrum antibiotics and examined their intestines after also taking probiotics. Probiotics actually "colonized" their gastrointestinal tract, but they did it at the expense of the normal intestinal microbiome, delaying by several months the return to its normal pre-antibiotic state.
This is not evidence of danger, but it is known that decreased microbial diversity after antibiotics may result in increased susceptibility to a multitude of chronic and infectious diseases. Thus, the low level of diversity allowed by probiotic colonization and the delay they cause in returning a person's intestinal microbiome to the pre-antibiotic state suggests that probiotics may not be harmless, as most seem to be think it.
Dr. Nicky Mehtani is a medical specialist in internal medicine and a member of the ABC News Medical Unit.
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