Short chain fatty acids are fatty acids with fewer than six carbon atoms, the smallest members of the fatty acid family. They include acetate, propionate, and butyrate, and their fame comes from the gut: colonic bacteria ferment dietary fibre into these acids, which feed the cells lining the colon, butyrate being their preferred fuel, calm inflammation, and influence metabolism and immunity throughout the body. This is the main mechanism by which fibre protects against bowel disease. Short chain fatty acids also occur in foods: butter is rich in butyric acid, which gives it part of its flavour, and vinegar is essentially dilute acetic acid. Small molecules, outsized importance.