Recommended daily allowance (RDA) for microbes?
By Prof. Colin Hill, Alimentary Pharmabiotic Centre, Food for Health Ireland, University College Cork
In this months’ issue of The Biochemist (August 2018) I explored the concept of whether or not there could be a health benefit to ingesting large numbers of safe microbes in our diet (see the open access article here). This was an effort, though I should stress not a scientifically rigorous effort, to consider the long history of encounters between humans and ingested microbes.
This opinion piece was prompted by a series of open questions which have often puzzled me. Why is so much of our immune system focussed on the gut? Why not simply let the microbes and food constituents pass through and get digested without such strict surveillance? Surely it would be more metabolically favourable to only react to those microbes that breach our epithelial barriers? Why does our enteric nervous system devote so much of its resources to the gut? Why is there a generally beneficial effect of many probiotics across so many health conditions? Why is mother’s milk designed to promote the growth of microbes?
Could the solution to all of these questions be down to a very simple answer? Because the gut ‘expects and requires’ constant encounters with microbes for full functionality. Given that humans evolved into a microbial world, and that we have consumed a diet rich in microbes for most of our evolutionary history, it makes sense that our enteric systems would be designed to appropriately deal with microbes of all types, selecting out those which can cause damage and destroying them, accommodating those which will become part of our microbiomes and letting the rest pass through. Surely we are monitoring and controlling our ‘microbial’ organ in the same way that our eukaryotic organs are monitored and controlled.
Could it be that the rise in autoimmune diseases could be, at least in part, due to an immune system primed to expect more microbes than it currently sees? Should we recommend that a daily dose of safe microbes should be included in dietary guidelines – in the form of more safe raw foods, more fermented foods and more probiotics? It must be emphasized that some serious pathogens must be controlled or eliminated from food – not ALL live microbes are safe. But the goal can be to process only when needed for safety reasons, so foods can be a source of the safe microbes they harbour.
Lots of questions, and not many answers. But I for one am taking account of this concept in my daily diet and am deliberately eating more microbes – I’ll let you know how it goes!