BY: DR. JASON BUSH
Solubility – the ability to mix completely into water without settling out – is a curious property when it comes to prebiotics. On one hand, soluble prebiotic supplements can be easily added to beverages or foods. They are also resistant to factors like heat and pressure used in modern food manufacturing processes, meaning that they are naturally present in many fruits and vegetables even after we cook them. But on the other hand, soluble prebiotics can create liquid imbalances in the intestines and this pressure can cause discomfort in the form of bloating. Combined with rapid fermentability, solubility limits the applicability of FODMAP prebiotics in sensitive individuals.
Whether a prebiotic is soluble or insoluble can also affect how it is fermented by the gut microbiome. In order to break down insoluble prebiotics, the healthy bacteria need to first attach themselves to the prebiotic. In a sense, this makes insoluble prebiotics a ‘destination’ for probiotics, causing them to group together. This can be beneficial because different bacteria work together to make the most of the prebiotic fermentation process, ultimately creating beneficial metabolites that positively influence our own physiology.
Insoluble prebiotics tend to be relatively large, and since the process generally involves ‘unwinding’ the molecules before they are fermented, these prebiotics are broken down over a longer period of time. As the contents of the large intestines slowly progress, this means that insoluble prebiotics are fermented along the length of the colon, likely prolonging and thoroughly distributing the beneficial effects.
How and where soluble prebiotics are fermented is more complex, and further research exploring the physical consequences of prebiotic solubility is needed. Insoluble prebiotics may fit less seamlessly into beverages and other food items, but their ability to bring probiotics together and provide prolonged fermentation are intuitively good reasons to consider adding more insoluble prebiotic fiber to your diet.