Do probiotics work?


Walk past the dairy case or health food section of any grocery store and you’ll see a variety of yogurts, milk, shakes and even granola bars that say they contain probiotics. These “good” bacteria are added to foods to promote a healthy environment of microorganisms in the digestive tract, supposedly to aid in digestion and promote good gastrointestinal health. Are these claims based in real science, or are they just another food fad to squeeze money out of consumers?

We spoke to Stefano Guandalini, MD, Section Chief of Pediatric Gastroenterology, Hepatology, and Nutrition and Medical Director of the Celiac Disease Center at the University of Chicago, about probiotics and prebiotics, the precursor that provides fuel for the supposedly beneficial bacteria. He and his colleagues published a review paper recently looking at various studies and clinical trials that used pre- and probiotics to treat symptoms of inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS) in children. The following is an edited version of that conversation.

Stefano Guandalini, MD

Many people are familiar with the term probiotics, but what are prebiotics?

Prebiotics are basically the metabolic fuel for probiotics. It’s a term that encompasses a number of mostly carbohydrates that are present in vegetables and grains, for instance in wheat, artichokes, legumes, etc. They are only partially digested by the human intestinal tract, so they reach the colon where they are fermented by bacteria. We have trillions of bacteria happily living in our colon, and they ferment these substrates. They’re happy with them, and so they thrive. The idea of taking prebiotics is that you can encourage the growth of good bacteria in the gut by providing them the food they like.

Can you do that by changing your diet? Or is there a pill you can take?

You can do in both ways. If your diet is rich in things like onions, garlic, wheat, legumes and artichokes, then you ingest a lot of prebiotics already. But there are also chemically identifiable supplements that also serve the same purpose.

Are prebiotics effective for treating digestive diseases?

In theory these are a good way of promoting a healthy microflora in your gut, and one would expect beneficial effects, but in reality it has been quite disappointing. There’s not a lot of practical use for prebiotics as we speak, in terms of clinical effectiveness. The only niche in which we found them to be successful is as an additive to formula for premature babies, because human milk actually contains plenty of prebiotics. Other than that, there hasn’t been much practical use. In fact, in our review, we saw that prebiotics have been tried for treating irritable bowel syndrome, but actually with mostly negative results.

With inflammatory bowel disease, it’s likely different. Several preparations have been tried with mixed results, but again, nothing sticks out as important or with clinical relevance. So in spite of good conceptual reasons to expect good results, they have not been proven very effective.

How are probiotics different from prebiotics?

Probiotics are microorganisms that, if ingested in adequate amounts, confer a health benefit to the host beyond the nutritional value. In practical terms, it’s a class of mostly live bacteria that have been studied for a long time and found useful for treating or preventing a number of clinical conditions.

Our review paper focuses on the efficacy of probiotics for IBS and IBD, including both ulcerative colitis and Crohn’s disease. For IBS, we have some good evidence in adults that some probiotics actually seem to be effective in relieving some of the symptoms, mostly the bloating and abdominal pain that accompanies IBS, especially when there is either diarrhea or constipation that goes along with it.

And in the case of ulcerative colitis, there is a growing body of evidence supporting the efficacy of some specific strains as an adjuvant in the course of the therapy. Crohn’s disease is different, however. People have tried multiple ways of addressing the problem with different strains of probiotics, different clinical settings, different endpoints, but none of the researchers were able to show any efficacy with probiotics in Crohn’s disease patients.

You can go into any grocery store and find yogurt and other foods that have probiotics added to them. Do those products do any good?

Not all probiotics are equal, that’s an important thing to stress. People think they can walk into a store and pick any probiotic from the shelf and they’re just the same. That is not the case. Different probiotics have different strains and concentrations of bacteria that have different properties. Only a minority of them has been tested properly in clinical trials to find if they were indeed effective.

In reality, yogurt by definition has to have two strains of bacteria—Lactobacillus bulgaricus and Streptococcus thermophilus—to create the yogurt. However these strains do not pass the gastrointestinal tract intact. They are destroyed by the acidity of the stomach and the enzymes of the pancreas, so nothing reaches the colon and it’s not beneficial. However, like you said, some yogurts are now enriched with other live bacteria of different strains. Some of them indeed include strains that survive the passage through the intestinal tract and then can be beneficial, and some make that claim but they don’t, and it’s hard for the general public to discriminate. Activia, for instance, is one of the good preparations. These yogurts actually do have strains of live Bifidobacteria that have been studied and may be beneficial. Yakult, containing well-studied strains of Lactobacilli, is another one that does the same.

Is a food product the best way to treat symptoms of IBS or IBD, or do you need a special preparation in a pill?

The best way is to use specific strains that have been validated through clinical trials and published in peer-reviewed journals to show efficacy, and if possible reproduced by different groups using the same preparations. So the list of probiotics that have gone through this process is actually very short:

  • There is a product called Align, based on a specific Bifidobacterium, which is mostly for adults with IBS.
  • For infants and colicky babies there is some proof of effectiveness for a product called Biogaia, which has the bacterium Lactobacillus reuteri in it.
  • Then we have Culturelle with Lactobacillus GG, another one with a long record of scientific, well conducted studies, which has been found effective in treating diarrheal diseases.
  • Florastor, which contains a yeast [Saccharomyces boulardii] instead of bacteria, is also effective in treating and preventing antibiotic associated diarrhea. Children who get antibiotics often develop diarrhea, and in many cases that can be prevented by the use of Florastor.
  • Finally there is a preparation called VSL #3, which is a highly concentrated preparation of 8 different strains of probiotics. This has received a great deal of attention by the scientific world to treat a number of conditions. It seems to be effective for ulcerative colitis, both in adults and children, and it has been found effective in irritable bowel syndrome as well.

Outside of this incredibly short list, however, there is nothing else. There is no other probiotic that has been found to be effective in rigorous, controlled clinical trials. This is not to say they aren’t working, it’s just to say we don’t have any scientific proof yet.

Are probiotics safe?

One thing that all these probiotics have in common is that they are relatively safe. They are very tolerable and basically create no side effects. One caveat is for premature babies and people with profoundly depressed immune systems. Some of these preparations might be contaminated by yeasts, which can be dangerous in those cases. But with these two exceptions, probiotics have been used in large amounts for generations now. So they are safe, but if there is no clear cut indication, I wouldn’t necessarily recommend them. That’s a question I often get from patients, “Could we use probiotics?” And if it’s not to treat a specific condition and they just think it will improve health, I tell them it’s not necessary.

Where is the research on prebiotics and probiotics headed?

It’s interesting. There was a boom for years and then it died down quite a bit. From a laboratory standpoint, we don’t understand a lot about how the probiotics work. So I think the attention of scientists now is more focused on understanding the mechanisms of the interactions between these bacteria and the host, which are different between different individuals. Each one of us has a unique composition of intestinal flora. The same probiotics may have a different effect for you and me, because they interact with trillions of other bacteria, which are different for each person. So all of these nuances are going back to basic science before moving further to the clinical arena.

That seems to be a theme of microbiome research. Everyone agrees on its profound effect on our health, but getting to where you could change something meaningfully to treat a disease is a different thing.

Right, we are not there yet. It’s very complicated. As we have said many times, the genome of the microbes is thousands of times more complex and more numerous than the human genome. When we are talking about personalized medicine, we are really talking about the microbiome: how to understand all the subtle interactions with the human host, and how to possibly exploit this for health reasons. It’s an incredibly interesting area, and my colleagues here at the University of Chicago, David Rubin, Eugene Chang, Cathryn Nagler, Bana Jabri and others are actively working on this. We aren’t there yet, but we will. I have great enthusiasm in this. I think this is the medicine of the future.

About Matt Wood (429 Articles)
Matt Wood is a senior science writer for the University of Chicago Medicine and editor of the Science Life blog.

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