Diarrhoea and diet
The passing of frequent, liquid stools, for which dietary management relies first on rehydration, then on choosing suitable fibre.
Diarrhoea is defined as at least three loose to liquid stools a day. It is acute when it lasts less than fourteen days (most often infectious in origin) and chronic beyond that, which then calls for a medical work-up.
The absolute priority is rehydration, because the loss of water and electrolytes is the real danger, particularly in children and older people. An oral rehydration solution, which combines water, sugar and salts in precise proportions, is far more effective than water alone: glucose is needed to carry sodium across the intestinal wall.
Not all fibre has the same effect, and this is where the classic mistake is made. Soluble fibre (pectin from cooked apple or banana, oats, white rice) forms a gel that slows transit and thickens stools: it is recommended. Insoluble fibre (bran, raw vegetables, fibrous vegetables, skins and pips) speeds up transit and makes things worse.
A few practical pointers: temporarily reduce lactose, as an irritated gut temporarily produces less lactase; avoid very sugary drinks, whose osmotic load draws water into the gut; and go back to normal eating as soon as possible rather than prolonging a restrictive diet, which delays repair of the gut lining.