Butyrate
A short-chain fatty acid produced when gut bacteria ferment fibre, the main energy source for the cells of the colon and a key player in the gut barrier.
Butyrate is a short-chain fatty acid (SCFA) produced in the colon when certain bacteria ferment fibre and resistant starch. Together with acetate and propionate, it makes up most of the SCFAs that result from this fermentation.
What sets it apart is that it is used on the spot: it supplies up to 70% of the energy of colonocytes, the cells lining the colon. These cells therefore do not rely on blood glucose but on a metabolite made by bacteria. It is the clearest illustration of the mutual dependence between a host and its microbiota.
This mechanism shows that fibre does more than keep you regular. It is often presented as a simple bulking agent. In reality, part of its value lies in feeding the bacteria that produce butyrate, which strengthens the tight junctions of the gut barrier and has a local anti-inflammatory effect.
The best sources are not food in the direct sense, because butyrate is produced, not eaten. What matters is therefore the substrates: resistant starch (potatoes or rice cooled after cooking), pulses, oats, under-ripe banana, and fermentable fibres such as inulin. The postbiotics and SCFA entries explain this framework in more detail.