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Not having a decent answer for this question led me to reach out to Mark Davis, ND, to see if he could offer an explanation. Dr. Davis practices in Maryland these days at the IBD Specialty Center (http://ibdspecialty.com/) in Bethesda, Maryland. He pointed out that there are a growing number of published clinical trials that report positive effects from taking dead probiotics, that is studies that used heat processed lactobacilli that could not grow in the gut.17-22 In most, though not all studies, these dead bacteria retained their therapeutic effects. Lactobacillido not need to grow, to have an effect. This is not how we have been describing how this works.
That bears repeating: Lactobacillineed not be alive to work. They need not colonize the patient's gut. If they don't have to be alive to work, there must be some factor within their 'bodies' or within their fragments, some factor X that triggers a response. Think of all the effort you and your patients have put into keeping those products refrigerated over the years; it may not have mattered.
Dr. Davis provided me a useful analogy in an email:
…so if its abundance is so tiny, how does Lactobacillus help? First of all, it doesn't seem implausible at all. Ultra-wealthy people are an inordinately small part of our population but they have a lot of influence on how society works. Politicians too, and doctors. There are all sorts of categories of humans that make up a tiny part of the population but influence the whole population for the better. So what's the mechanism of action?... I've thought that the way that other microbes in the gut and our own immune system are reacting to (probably proteins in) probiotic bacteria may be more important than the actual work the probiotic bacteria themselves are doing.
Maybe Dr. Davis is correct; maybe he's not. The thing is that we take it for granted that these probiotics help a wide range of conditions and yet if we stop and look carefully, we really do not understand how or why lactobacilli do what they do.
For many years I used a simple analogy with patients to explain why lactic acid-producing bacteria were so beneficial: it's like preserving vegetables by canning – the whole Mason jar, pressure cooker production:
All foods can be divided into one of two categories when canning. They are either ‘'acid-safe' or 'non acid-safe'. Foods that are acidic, say tomato products, whole tomatoes, puree or sauce, have a low pH and are acid-safe. You cook them up, pour the stuff in clean jars and put a lid on it. Period, done. Dangerous bacteria cannot grow in an acid environment. Foods with a higher pH are not so safe. With non-acid foods you pack the food into sterile jars, then heat process it in a pressure cooker in the hope of sterilizing it and once done, throw the contents in the compost out of fear of botulism. The difference is pH. Pathogens don't survive long in acid. Same thing happens in your gut. Probiotics lower the gut pH and keep out unwanted bacteria.
It sounds good but is obviously not accurate. If dead bacteria still have effect, this whole image we have of the tiny amounts of lactobacillithat we take as probiotics supplements repopulating the gut with their offspring is not what happens. Instead some surviving constituent of these bacteria drastically shift populations of other bacteria as they pass through the gut. What is this 'factor'?
When Columbus reached the New World, he thought he had reached India. He was totally wrong of course. I suspect that our understanding of gut microbiology may be as accurate as any map Columbus might have drawn of the world. He was missing a few key facts, there was that whole North America business. Lactobacilli may be our equivalent of Columbus and the East Indies. We may be more certain of where we are than we should be….
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Jacob Schor, ND, FABNO