What’s the story on probiotics?

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Dear Cecil: I’ve been hearing a lot about probiotics lately. I can see where the concept might be a good idea, but I have one question: After you’ve taken a probiotic supplement and established a colony of good bacteria in your intestinal tract, why do you have to keep taking it (other than to maintain someone’s boat payments)? Shouldn’t the colony you’ve established be self-sustaining? Ken Sweetman


Illustration by Slug Signorino

Cecil replies:

Not possible, my friend. At any rate not easily. I’m afraid probiotics have been a bit oversold.

Your digestive tract is a teeming zoo of more than 100 trillion bacteria cells representing hundreds of different species and in the aggregate weighing an average of seven pounds. A teaspoonful of probiotic supplement, if we may trust a random online promotion, contains 4 billion organisms. In other words, the bacteria in your gut outnumber those in the spoon 25,000 to 1. The chances are strong the newly introduced microbes won’t establish anything of importance, let alone a colony, during their transit down your alimentary canal. At best they may provide some ephemeral benefit, although there’s no guarantee of even that.

For those new to the concept, probiotics are foods or supplements containing viable “good” bacteria and yeasts meant to help digest food, protect against dangerous bacteria, and build up the immune system. Some assert that a deficit of beneficial bacteria can lead to serious GI trouble including irritable bowel syndrome, infectious diarrhea, necrotizing enterocolitis, and ulcers.

Scientists have long known the bacteria in a healthy digestive tract differed from those in someone who was ailing. A century ago some proposed that rather than live with a gut full of bad bacteria, one might eat certain foods to modify one’s microbial demographics. Milk products, yogurt especially, provide probiotic benefits, but on the whole (the theory goes) our modern diet is deficient in helpful bacteria in part as a side effect of modern cleanliness: we encounter fewer bacteria of any kind due to pasteurization and other food processing, as well as drugs, additives, and so on that suppress normal bacteria.

There’s some truth to this. A round of antibiotics can kill off your intestinal flora, necessitating (at minimum) frequent trips to the loo. If this happens to you — and it happens to about a third of those so treated — there’s a roughly 40 percent chance probiotics will ease your distress. Likewise, someone whose bacteria reservoir has been reduced after having a section of their gut surgically removed may be advised to consume yogurt or probiotic supplements to help make up the deficit.

But these are exceptional cases, and the evidence suggests it’s chiefly in the exceptional cases that probiotics may be of use rather than as a preventive measure. One thing about gut bacteria: when their little lives are troubled, they let you know. Diarrhea is the least of it. Some examples of instances in which probiotics have proven helpful:

  • Pouchitis, an inflammation of the gut tissue in colostomy patients, responded well to probiotic treatment, with an 83 percent reduction in occurrence.
  • Probiotics significantly reduce the frequency of ulcerative colitis attacks.
  • Children susceptible to eczema saw significantly fewer outbreaks through age four when treated with probiotics.

OK, eczema prevention is a non-obvious benefit of goosed-up gut bacteria. On the whole, however, evidence for the broader benefits of probiotic supplements is limited. For instance, a study of overweight adults who drank fermented milk containing probiotic bacteria found they lost both fat and weight relative to control subjects. But the study was small, with just 43 subjects.

Even in some conditions where you’d figure they’d help the most — e.g., those directly involving the gut and the bacteria therein — probiotics provide little or no value. A meta-analysis of research involving eleven different types of probiotic bacteria and eight different gastrointestinal diseases (including the pouchitis success story mentioned above) professed to show probiotics improved both prevention and treatment by 42 percent. However, generalizing across a broad range of conditions, goals, and therapeutic agents is inherently iffy. Examples of intestinal ailments where high hopes for probiotics have gone bust include necrotizing enterocolitis, sometimes seen in premature infants who lack protective bacteria; irritable bowel syndrome; and Crohn’s disease.

That hasn’t stopped some from promoting probiotics as a Crohn’s cure. Claims that probiotics can help fight hypertension, HIV/AIDS, and cancer are likewise unsupported.

Disappointed? You needn’t be. Let me tell you about extreme probiotics, more commonly known as fecal transplantation. It’s pretty much what it sounds like. Stop making eww noises: fecal transplants have been shown to be effective in treating Clostridium difficile disease (CDD), a complication of gut bacteria loss due to antibiotic use that as of 2007 was killing more than 14,000 Americans a year. Needless to say, the procedure is more involved than swallowing a few pills, and no one would suggest it as a preventive measure. But if you honest to God need to establish a self-sustaining colony of good bacteria in your gut — indisputably the number-one thing on your to-do list if you have CDD — here’s a treatment that works.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.