Author: Leo Akin
What are Probiotics?
Probiotics are microbes that confer some health benefits on their hosts. For humans, the most important probiotics are the microbes living in the gastrointestinal tract and most of the probiotic microbes in the gut are bacteria. These gut microbes outnumber human cells by 10 to 1 and they are essential to our health especially to the functioning of the immune system. Gut probiotics fulfil specific roles too. For example, we need these microbes to synthesize vitamin K and to absorb certain nutrients. On the other hand, there are also pathogenic microbes in the gut. The probiotics keep the pathogens in check and this balance is achieved with a healthy gut flora. However, when it is destroyed, pathogens may predominate and then damage the lining of the gastrointestinal tract.
When a healthy gut flora is destroyed, the resulting dominance of pathogens can result in gastrointestinal infections, increased permeability of the gut (leaky gut syndrome) and disruption of the immune system. The loss of healthy gut flora has been identified as the one of the causes of a number of conditions ranging from inflammatory bowel disease toeczema. These conditions are easily treated by restoring healthy microbes to the gut environment. Probiotics are used to restore damaged gut flora. The most common probiotics used for this purpose are the bacteria belonging in the Lactobacillus and Bifidobacteria families. Probiotics are available as supplements but they can also be found in certain fermented foods such as yogurt. Their effectiveness and safety are well-established.
What are Prebiotics?
To improve the efficacy of probiotics, prebiotics are sometimes added. Prebiotics serve as food sources for probiotic bacteria. The ideal prebiotic must be indigestible to humans and yet be useful to the probiotics living in the gut. Because it is indigestible, the ideal prebiotic is safe for human consumption since it never reaches systemic circulation but rather eliminated by excretion. Prebiotics are commonly found in nature. They are found in certain plants and yeasts such as Aspergillus.
One of the most commonly used prebiotic is inulin. Inulin is a complex carbohydrate found in vegetables such as Jerusalem artichoke, chicory root and asparagus. Some of the other food sources of inulin include leek, garlic, onion, banana, wheat and barley. Structurally, inulin is a sugar polymer. Each molecule of the prebiotic is made up of 10 – 70 molecules of D-fructose. A shorter metabolite of inulin called FOS (fructooligosaccharide) is a common replacement for inulin in probiotic products. FOS is also referred to as oligofructan or oligofructose. It is made up of a maximum of 7 fructose molecules and is, therefore, produced from the breakdown of inulin.
Why You Should Avoid FOS and Other Prebiotics
Besides their main role as a food source for probiotic microbes, FOS and other commonly used prebiotics are also added to probiotics to serve as sweeteners. Because they are short-chain polymers of fructose, these prebiotics are much more easily broken down (compared to inulin and other complex carbohydrates). On one hand, this ease of degradation means that they can quickly release fructose (energy source) to probiotics. On the other hand, making fructose readily and easily available means that humans can also absorb it. Therefore, these short-chain probiotics may increase your caloric intake and raise blood sugar level.
However, prebiotics are dangerous for another reason that is also closely tied to one of their advantages. Prebiotics like FOS may serve as food sources for “good” bacteria but they are really simply food sources. This means that there is no guarantee that they are only feeding probiotics. They can also promote the growth of pathogens in the gut. Currently, there is evidence to indicate that certain pathogens can break down prebiotics in the same way that probiotics do. In addition, researchers believe that evolutionary competition will drive more pathogens to adapt prebiotics as food sources.
Examples of pathogens that can already digest prebiotics include bacteria such as Klebsiella and E. coli as well as yeasts such as Clostridium. These are some of the worst pathogens in the gut and they are only kept in check by probiotics. When prebiotics feed both pathogens and probiotics, it becomes even harder to restore a healthy gut flora. Furthermore, this means that probiotics and prebiotics have equal chances of predominating. In summary, prebiotics do not really improve the efficacy of probiotics in the long run. Any brief advantage enjoyed by probiotics will soon be reversed as pathogens take to prebiotics too.
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