New research has found that taking probiotics seemed "useless in many cases" and could have adverse side effects when taken after antibiotics.
Experiments conducted in the bowels of people discovered that the ability of probiotics to increase the number of good bacteria in the intestine depends on the bacteria that are already present in the intestine.
Instead of examining faeces or stool samples, researchers in Israel, for the first time, took samples from inside the bowels of 25 people by using a tube.
Generic priobiotic strains were administered to one group and a placebo was administered to the other. The results were taken before and during the two months after taking the probiotic or placebo.
The results showed that the new samples were much more representative of the amount of good bacteria that remain alive in a person's gut.
The authors of the research published in the journal Cell We recommend that the use of probiotics be tailored to people based on the bacteria that are already in the gut and their health needs.
"If some people resist and only some people allow it, the benefits of standard probiotics that we all take can not be as universal as we once thought," said study co-author and immunologist Eran Elinav.
"These results highlight the role of the intestinal microbiome in driving very specific clinical differences between people."
In a second study, conducted by the same research group, 21 people received a course of antibiotics and then divided into three groups.
The first group received no treatment, the second group used generic probiotics and the third group was treated with a faecal microbiome transplant using their own bacteria, which had been collected before taking the antibiotic.
The second group achieved immediate results with the antibiotics clearing the way for probiotics to colonize the intestine easily, but the process of returning the intestinal microbiome to a normal state took months.
"Contrary to the current dogma that probiotics are harmless and benefit everyone, these results reveal a potentially new adverse side effect of the use of probiotics with antibiotics that could even have long-term consequences," Elinav said.
"On the contrary, the replenishment of the intestine with the microbes themselves is a personalized treatment designed by mother nature that led to a total reversal of the effects of antibiotics."
The coauthor and computational biologist Eran Segal said that the study shows that the universal consumption of probiotics should be moderate.
"This opens the door to diagnoses that would take us from a universal empirical consumption of probiotics, which seems useless in many cases, to one that adapts to the individual and can be prescribed to different individuals depending on their initial characteristics."
Probiotics can be found in supplements and fermented foods such as pickles, kimchi, sauerkraut and yogurt, as well as in cheese and chocolate.
A review of 313 randomized controlled trials, published in BMH in June, it was found that taking probiotics helped prevent diarrhea, bronchitis and eczema.
The studies also noted improvements in reducing the risk of heart disease and reducing the markers of inflammation in the blood.