Rehydration drinks: the St Mark’s and Oxford recipes

Rehydration drinks are often called sugar-salt or carbohydrate-electrolyte solutions. Two of the published recipes can be made at home, and both end with the same instruction: chill, flavour as desired, and sip throughout the day.

Shop-bought sachets

In the short term, commercially available solutions such as Dioralyte can be used, and similar pharmacy products may be suitable too. There is an important caveat: to reach the right concentration — more concentrated than the fluid in the body’s cells, so the body absorbs it — they need to be made double strength, two sachets in a glass of water. They should not be taken in that form for long, as they are too high in potassium.

Two things already in the kitchen

• Good quality coconut water — not coconut milk — is described as a good hydrator: a high concentration of simple sugars, electrolytes and minerals, more concentrated than the fluid in the body’s cells.
• Low fat cow’s milk is also named as a good hydrator, and one usually already at home, with the exception noted for people who are lactose intolerant.

Why sipping, not gulping

Both recipes end with the same instruction — sip throughout the day — and it is not a stylistic flourish. The whole mechanism these drinks rely on is concentration: a fluid more concentrated than the fluid in the body’s cells is drawn in, taking salt and water with it. Drinking a litre at once does not raise the concentration in the small intestine for any longer than drinking it steadily does, and steady is what keeps absorption going.

When to reach for one

The situations where salt and water go out faster than usual: output that is very watery or loose, hot weather, physical exercise, vomiting, or already feeling extra thirsty. Two more get added for travel — too much alcohol accelerates dehydration, and coffee is a diuretic that can deplete reserves.

When output is high there is a ratio worth remembering: restrict oral fluids to 1.5 litres per 24 hours, avoiding caffeine, fruit juice and alcohol — and make one litre of that an oral rehydration solution. That is a much larger share than most people would guess, and it is the point where a home-made solution stops being a novelty and starts being the main drink of the day.

The other half of the same advice is not to drink your way out of trouble the other way. The advice is firm that you should not try to regulate output by cutting down on fluids, because you may become dehydrated: use a rehydration solution when necessary instead.