Probiotics or Prebiotics: which would Darwin choose?
“Darwin” you are probably wondering, “what does he have to do with this?” A better choice might have been the Nobel prize-winning Russian zoologist Elie Metchnikoff (though few would recognize his name). He, like Darwin, exerted almost clairvoyant-like insight into biology and medicine, and his observation that many Bulgarians who consumed foods fermented with Lactobacilli bacteria lived, on average, to 90 years of age, effectively minted him as “The Father of Probiotics”.
Élie Metchnikoff (1845-1916)
As for Darwin, a boat named after a dog and some swimming lizards on the Galapagos Islands is usually what comes to mind. And a pesky little book he wrote 150 years ago that people in Kansas can’t seem to get comfortable with. None of which on the surface appear to have anything to do with probiotics and prebiotics. However, Darwin’s wide-ranging worldview, experiments, and writings embraced the diverse disciplines of natural history, ecology, ethology, anthropology, genetics, and of course, evolution, making his potential take on it all interesting.
Metchnikoff was only fourteen years of age when Darwin made his big splash with his tome on evolution in 1859. By the early 1900s his bioprospecting in Bulgaria was driving the rise of a modern yogurt industry on the proposition that Bacillus bulgaricus, now called Lactobacillus bulgaricus, could transform the “toxic flora of the large intestine into a host friendly colony of B. bulgaricus.” Like Darwin, and armed with the advantages of Darwin’s wide-reaching theories, Metchnikoff’s writings were as equally multi-disciplinary covering embryogenesis, pathology, and most importantly, inflammation and immunity.
But I like to think, if the advantages and transfer of knowledge were reversed, and it was Darwin who was armed with in some kind of crystal-ball-time-machine-thingy that provided him access to early twentieth-century knowledge of a practical scientist and pondering philosopher such as Metchnikoff, could he have made more of the tiny microbes and their implications for human health? Would Darwin have eagerly pursued and promoted probiotics as Metchnikoff had, or would he have thought more of prebiotics? (In order for Darwin to have considered prebiotics, he would have to set his time machine dial a little farther ahead, to 1995, when the concept was first introduced. But you get the idea. Keep reading).
According the World Health Organization, probiotics are live microorganisms which when administered in adequate amount confer a health benefit on the host. As for prebiotics, these are a selectively fermented ingredient (fiber) that results in specific changes in the composition and/or activity of the gastrointestinal microbiota, thus conferring benefit(s) upon host health. In other words, probiotics are live microbes and prebiotics are food for microbes.
Since probiotics have been on the research radar for nearly a century now, the published literature is massive, mostly paid for by industry, and not always conclusive. For prebiotics, having only been a concept since 1995, the literature is less extensive, but also mostly paid for by industry, and more often than not, more definitive.
The idea behind probiotics is fairly straightforward and aims to reinstate, more or less, balance in your intestinal flora and improve whatever aberration is bothering you. This runs the gambit from eczema, irritable bowel disease, mood and so on. Probiotics’ weakness, in spite of overall positive results in some dose specific studies, is determining which micro-organisms are best and in which combination. The issue of dosage is also important and always complicated by degradation from things like manufacturing, shelf life and acidic human stomachs, all of which tend to reduce probiotic numbers before they can reach their target (the human colon more often than not). While “5 Billion Probiotic Cultures” on the label sounds great, those could fit on the tip of a pen. How many actually reach your colon where they might do some good? Manufacturers are working hard to address these issues as a more discerning public gets wearier of claims on food and supplement packages.
From the perspective of someone like Darwin, he would likely question the ability of a single strain of bacteria to impact on the vast inner ecosystem of the human gut. While we have recently only discovered that extraordinary diversity and richness of the human gut microbiome, Metchnikoff-era folks had some basic idea of the diversity of microbial life. A simple thought experiment Darwin may have undertaken may have been the analogy to a tropical rainforest, with its thousands of species of trees, flowering plants, mammals, birds, fish, reptiles, amphibians all encased in a warm and wet organic blanket topped with a canopy. The human gut is also warm and wet and home to tens of thousands of species and subspecies. Taking a probiotic – of any strain – and hoping it modifies your inner ecosystem in any meaningful way would be akin to planting a single species of flower on the forest floor at the base of a 200 foot tall tree and thinking this tiny contribution will tip the ecological balance. Maybe? But it would be fleeting at best and confined to a tiny plot of the forest floor.
This fleeting problem is what got the good folks over at Danone in trouble with their commercials of Jamie Lee Curtis peddling the magic elixir Activia. Seems in order for the product to have any effect, it needed to be consumed multiple times a day, a tiny detail that Jamie forget to tell us. The $21M fine leveed by the FTC should help them remember to include that particular point from now on.
Darwin may also have thought that the concept of prebiotics was interesting, but may have asked, “why only stimulate the growth of a certain group of bacteria?” – similar to the rainforest analogy above. A nice body of literature clearly demonstrates that prebiotics, such as the special inulin and oligosaccharides (fiber) from chicory roots (the most commonly used prebiotic fiber), selectively promote the growth of bifidobacterium and other lactic acid bacteria, a group of bacteria that seem to be associated with reducing infection from pathogens, improved gut permeability, increased calcium absorption and so on. Importantly, a true prebiotic is selective, in that it does not promote the growth of less desirable bacteria like Clostridium.
As with probiotics, a certain daily dosage is necessary to achieve a bifidogenic affect, which appears to be around 4-8g a day. Unless you take a prebiotic supplement or fortified food – which the industry would like you to do – your best bet would be common foods like Jerusalem artichokes, dandelion greens, onion, garlic, leek, and asparagus. Although fibers with special prebiotic effects are found in more than 30,000 plants worldwide, most we can’t find at our local grocery store (e.g., Yam Daisy) and the prebiotics occur in such small quantities as to be almost meaningless. If you are feeling enthusiastic, you could achieve a bifidogenic affect from peeling back and downing 1.5 to 2 pounds of bananas. A little less than 2 ounces of leek or garlic would do the trick as well.
From Darwin’s ecological perspective on the world, he may have not advocated for either. His research into earthworms, which resulted in the publication in 1881 of his book The Formation of Vegetable Mould Through the Action of Worms, with Observations on Their Habits, which apparently sold as many copies as On the Origin of Species, may have also contributed to this conclusion as well. Unencumbered at his time in history by the free market machine of the modern world, he may have asked the obvious question of, “If the microbes of interest are already in you, why not just feed them and the other potentially beneficial microbes the diet they were likely selected upon over time, evolutionary time.”
Working from Metchnikoff’s observation that societies that consume fermented products seemed to live longer, Darwin may have reasoned that while bacteria in milk is interesting, maybe it’s the totality of the natural environment of those milkers and fermenters – dirt, dung, cowshed and all – that support a time-honored symbiotic relationship with all microbes, not just the easily isolated Bacillus bulgaricus. His own well-documented ill-health and homeopathic remedies, along with his observations of the symbiotic relationship between earthworms, soil and agriculture, may have pushed him closer to our modern concepts of the Hygiene Hypothesis and Germ Theory for disease.
He may have also reasoned that as species change habitat and thus diet, they either adapt or die, but that evolution and adaptation take time, also leading to the observation that biodiversity in ecological systems result better functioning and stable communities. In the case of prebiotics, why just one, why not ingest a diversity of natural foods (fibers) that would promote diversity in the human-microbe ecosystem. This would broaden the definition of a bifidogenic or positive affect and free it from the bounds of regulatory or industry definition.
I suspect that the very nature of probiotics will change, including who gets to sell them, what form they are delivered in and definitely the associated health claims. There is already regulatory rumbling, spurred on by the pharmaceutical industry, that probiotics should be regulated and held to the same clinical trial standards as other subsistences (drugs) used to treat or attenuate disease. It is likely that probiotics will become cocktails of dozens if not hundreds of long-term community strains, delivered as a fecal transplant in capsule. Dubbed fecal microbiota transplantation, or fecal bacteriotherapy, the practice is showing some amazing results treating infections of the large bowel. So rather than plant a single daisy at the base of a 200 foot tree, plant entire fields seeded from the nursery of a healthy donor’s intestinal tract. However, these precision probiotics of the future still do not address the basic problem of why a particular person is out of balance in the first place.
The same goes for the concept of prebiotics. A nifty concept that has drawn much needed attention to the ability to modulate ones intestinal flora with diet, it would be unfortunate if consumers didn’t seize on this information and take the next logical step and improve overall intestinal balance by increasing the quantity and diversity of dietary fiber in their diet through whole foods. We will likely see more synbiotics as well – combinations of prebiotics and probiotics.
None of this suggest that yogurt with its billions of live cultures is a bad thing, or that a pizza crust fortified with prebiotic fiber should be avoided. With the avalanche of studies linking an imbalance in our gut microbiome to disease, and our ability to regulate this with diet and lifestyle in some positive ways well within our grasp, we are presented with our very own Bulgarian-moment circa 2012. The health of the planet is in free fall. If we don’t start paying attention to some basics of human ecology, evolution, anthropology, and natural history, then we all might end up getting nominated for the Darwin Awards.