What 100 Trillion Microorganisms Want You To Eat — Part Three: Postbiotics
I want to complete my series of articles on foods that are important for a healthy gut microbiome by talking about the third and most recently recognised member of the family: postbiotics. These are compounds produced by beneficial bacteria as they break down fermentable fibre — in other words, the ‘end products’ of probiotic activity that support digestion, immunity, and overall good health.
Unlike probiotics, which are live bacteria, there are several different categories of postbiotics, all of which are non-living:
Organic acids such as the lactic acid or acetic acid found in yoghurt, kefir, fermented vegetables, and aged cheese, which aid digestion overall.
Short-chain fatty acids such as butyrate, propionate, and acetate.
Vitamins such as vitamin K2, which plays a critical role in ensuring that calcium is deposited in your bones rather than your arteries, and certain B vitamins — specifically B12, folate, and biotin.
Bacteriocins, which are antimicrobial compounds that help keep pathogenic bacteria in check.
Enzymes. Beneficial gut bacteria produce a range of enzymes that support digestion and nutrient absorption — breaking down compounds that your own digestive system cannot, and making certain nutrients more bioavailable.
Cell wall fragments from bacteria such as lactobacillus or bifidobacteria, which also provide antimicrobial benefits.
Signalling molecules including neurotransmitters like serotonin, 90 percent of which is actually made in our gut.
Postbiotics can be produced in two distinctly different ways — in our gut itself, as byproducts of the fermentation of certain fibres found in prebiotic foods, and in fermented and cultured foods, which may be either raw or cooked. Kefir, for example, which we know as a probiotic food because of its beneficial bacteria, also contains postbiotics in the form of lactic acid. In the same way, traditionally made, long-fermented sourdough bread also contains postbiotics, as even though the live lactobacillus bacteria are killed during baking, the inactivated bacterial cells and their beneficial byproducts remain. The same applies to any fermented or cultured food that has been cooked or heated: miso stirred into a hot soup, fermented vegetables added to a warm dish, or aged cheese stirred through a sauce. The live cultures may be gone, but the beneficial components remain and can still confer health benefits. I find this fascinating as I had always assumed that heating probiotic foods was a definite no.
We actually touched on postbiotics in my first two articles when we discussed butyrate, which is one of the more important ones. This is because butyrate (and to a lesser extent propionate and acetate) helps to keep our immune system strong by feeding colonocytes, the cells that form the barrier between our gut and our bloodstream. A strong gut barrier protects against undigested food, pathogenic bacteria, and other metabolic waste products finding their way into the blood, which can contribute to conditions such as irritable bowel syndrome. Butyrate also helps stabilise blood sugar, support healthy weight, and even regulate mood through the gut-brain axis.
Bringing it all together
One of the things I find most compelling about the prebiotic-probiotic-postbiotic picture is how nicely it all connects together. If you eat a wide variety of fibrous foods your beneficial bacteria will be well fed. If you eat lots of fermented and cultured foods, you replenish and diversify those bacteria. And when both of those things are happening consistently, your microbiome will then produce a rich array of postbiotic compounds e.g. butyrate, vitamins, bacteriocins, enzymes and signalling molecules, all of which will support your health in ways that extend far beyond digestion.
It is, in other words, a system. And like most biological systems, it rewards consistency rather than perfection. You don’t need to overhaul your diet overnight or take an array of supplements. In fact, if you are new to all of this, you may wish to introduce fermentable fibre slowly into your diet to avoid digestive discomfort as your body adapts. The most important thing is just to feed your 100 trillion microorganisms as well as you can, and then let them do what they have evolved over thousands of years to do.