Dec 18 2008

A New Analysis of Probiotics

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A few months ago I blogged about so-called “good” bacteria. We are colonized by friendly bacteria that do not cause infections or harm, and in fact serve vital functions.

One of the specific topics I covered was probiotics – use of friendly bacteria species to improve the bacteria in our guts to help stave off infection or otherwise promote GI (gastrointestinal) health. Based on the evidence at the time I was luke warm on probiotics – the concept is sound, but the evidence for specific benefits is preliminary.

A new study, actually a meta-analysis and review of existing studies, published in the American Family Physician, has altered my assessment to be more positive.

Kligler and Cohrssen reviewed dozens of studies, and also prior reviews, such as Cochrane reviews, which are the standard for evidence-based medicine. They conclude:

Probiotics are microorganisms with potential health benefits. They may be used to prevent and treat antibiotic-associated diarrhea and acute infectious diarrhea. They may also be effective in relieving symptoms of irritable bowel syndrome, and in treating atopic dermatitis in children.

In thinking about any medical treatment it is important to note that specific treatments need to be assessed as to their safety and effectiveness in treating specific conditions. It is important to avoid oversimplifications, such as “probiotics work” – work for what, and in what dose?

Unfortunately, there is a natural tendency to oversimplify – it is one way to have a sense of control over our complex and often overwhelming world. Simplification, in fact, is necessary. We need to approximate reality with rules and characterizations that are mostly true most of the time. Oversimplification, however, implies that this process is taken to the extreme of being wrong. This is dangerous, or at least wasteful, when it comes to medicine.

With regard to probiotics, what this review supports is that certain doses of specific species of bacteria can help reduce the risk of developing diarrhea and the severity of diarrhea if it does develop. The concept is that friendly bacteria form a carpet lining all our mucous membranes. This carpet of bacteria keeps out any invading infectious bacteria, or at least limits its ability to multiply. When bacterial numbers ar reduced by antibiotics, this opens the door for infections from either viruses or resistant bacteria.

Taking some probiotic during antibiotic use reduces the risk of infectious diarrhea. It seems that these probiotic bacteria can help replace the killed good bacteria and keep our infections. There is even a dose response effect – 10 billion colony forming units of bacteria are better than 5 billion colony forming units.

However, the probiotics must be taking within 3 days of starting the antibiotic and the benefits are short lived. This is because the bacteria in probiotic products (like yogurt) do not seem to set up shop – they don’t form permanent self-sustaining colonies in the gut.  So they only help if you are actively taking them in large amounts while you need them.

Another limitation of probiotics is that they contain only one or a few species of bacteria. Meanwhile, our guts contain hundreds of species forming a real ecosystem. Adding a couple of species does not have a significant benefit to the ecosytem, which will have to recover its full diversity on its own over time.

So probiotics are not a cure, but they can be an effective band-aid. They can help crowd out infectious organisms during antibiotic use. They also appear to be relatively safe, so there is little downside to taking them except for the expense.

There is also evidence, although of less quality according to this review, to support the use of probiotics to relieve the symptoms of irritable bowel syndrome and atopic dermatitis. The evidence for these indications is more preliminary.

Here comes the risk of oversimplification – there is already an industry of probiotic products based upon the claim that routine use of probiotics has health benefits. There is no evidence for this, however. Evidence for a short-lived benefit during antibiotic use cannot be used to support the routine use of probiotics in the healthy.

A Google search on “probiotics” brings up many legitimate health advice sites that give a reasonable review of the evidence. It also brings up the websites of companies selling probiotics – and there is a clear disconnect between the evidence-based information at, say, WebMD, and the marketing hype promoting probiotic products (no surprise there).

Getrightprobiotics, for example, claims:

Patented Bio-tract technology promotes a healthy digestive tract. Reduce lactose intolerance, diarrhea, constipation, IBS, IBD, and more.

The first claim is simply a “structure-function” claim – promoting a healthy digestive tract. There is no credible evidence or scientific consensus for this claim, but in the US companies are free to make such claims without any oversight or evidence.  Evidence for lactose intolerance and IBS are preliminary and lack consensus. For diarrhea, as I discussed above, the benefits are short-lived and only during antibiotic use.

But companies do not want people to use their probiotic products only for occasional short periods of time, they want them to use them every day. So that is the claim they make.

Perhaps the bigger problem, though, is that probiotics are regulated like supplements (which means hardly at all). Therefore it is very difficult to know how to apply the evidence to any particular product. Some information should be readily available on labels – what bacterial species are claimed to be present and it what amounts. The evidence suggests that at least 5 billion bacteria, or colony forming units (meaning live bacteria able to reproduce) are required for benefits, and 10 billion are better. But some product boast 4 billion bacteria – which sounds like a lot, even though it is a low dose.

There is also no standard quality control. Are the bacteria said to be present really in the product? How pure is the culture? Are they alive in the numbers claimed?

For pharmaceuticals when a patent expires and companies are able to produce generic alternatives, they have to do studies to demonstrate equivalence to the approved brand name drug – even though they are still producing the same active ingredient, the same molecule. There is no such requirement for probiotics.


Overall, I am actually supportive of the concept of probiotics. The theory is sound, it is likely a low risk intervention, and I think there is tremendous potential for the future. This latest review pushes me over the threshold of concluding that certain probiotics in sufficient doses are safe and effective for temporary prevention and treatment of antibiotic-associated diarrhea. There are other plausible indications with some positive evidence, but more study is needed.

However, the application of this scientific data is frustrated by an unregulated market for probiotics. The marketing claims being made go well beyond the evidence, emphasize continuous as opposed to as-needed use, and there is no standardization. Consumers are therefore not being well served. There is some independent analysis available, but this only looks at the content and quality of products, not health claims.

What we need is not only better quality control for products, but effective regulation of the health claims made for these products. And this regulation should be based upon clinical studies showing efficacy of specific products for specific indications or benefits.

Otherwise, use of probiotics by consumers is a crap-shoot.

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