The effect of probiotics largely depends on the bacteria that are already in the stomach, researchers have discovered, through samples taken from people’s stomachs.
The researchers sought to find out how much probiotics change the composition of microbes in the stomach and what chemical compounds they produce.
Probiotics are edible live microbes—mostly bacteria—that can provide health benefits. They can be found in or added to foods like yogurt, taken as dietary supplements, or added to drugs.
For a microbe to be considered a probiotic, it must survive the acid environment of the stomach and it must boost the number of good bacteria in the gut. Also, probiotic microbes may grow colonies by attaching to tiny hairs that exist in the intestines. They can produce certain substances, such as a vitamin or chemical compound that can kill disease-causing bugs, such as diarrhea viruses.
Probiotics are sometimes sold as supplements. RomarioIen/Shutterstock
This relatively new field of study has so far been limited to scientists analyzing the bacteria in stool samples of people in an effort to learn what effects probiotics have on the types of microbes in our gut.
But this approach doesn’t reveal whether microbes are forming colonies or causing changes in the digestive tract. To answer these questions, scientists in Israel found 15 volunteers to undergo two invasive colonoscopy and endoscopy procedures, one at baseline and another during consumption of probiotics or placebo.
Their data revealed that the bacteria measured from stool samples isn’t very representative of what goes on in the whole gut. That is likely because the microbes measured in stool samples are more like those from the lower part of the gut than those higher up in the gut, closer to the small bowel.
The researchers found that many of the good microbes that were eaten as probiotics didn’t attach to the tiny hairs in the gut and simply traveled through the stomach to be excreted. In other words, the amounts of these bacteria in feces weren’t representative of how many good bacteria actually managed to stay alive inside the person’s gut.
However, they were able to confirm that probiotic supplements did change the chemical compounds that are produced in the gut.
The most important finding to come out of this study is that the response to probiotics changes among individuals, and that any health effects will depend on the bacteria already present in the gut.
The authors conclude that the one-size-fits-all approach to probiotics isn’t ideal and that it would be better to tailor probiotics to individuals, depending both on the health benefits they need, and on the microbes already living in their guts.
Are Probiotics Worth Taking?
Does taking probiotics do any good? The short answer is yes—but it could be better.
Some colleagues and I recently searched the scientific literature and found 313 good quality clinical studies and randomized controlled trials involving almost 50,000 people where researchers had investigated the health benefits of taking probiotics or taking a placebo.
Our analysis showed that taking probiotics can help prevent diarrhea, bronchitis, and eczema. Probiotics also seem to reduce heart disease risk and reduce substances in the blood that have to do with inflammation.
So while probiotics rarely permanently change the microbe composition of the gut, they can affect health, perhaps by improving our immune system or producing beneficial chemicals. And if it becomes possible to tailor probiotics to an individual’s characteristics, then probiotics may actually be much more effective than they are now.
