Ask Dr Gary: DIY tonic works wonders

A lot of miserable-looking kids come to the emergency department with fevers and mild dehydration. They have a cold or flu, are not drinking enough and are losing more fluid than normal because of their fever or diarrhoea.

Their lips and tongues are dry and they are listless or irritable.

Two hours later, after little more than a cup of Pedialyte from the nurse at the front door, many of them look like new - smiling, playful and happy.

Their parents apologise for bringing them in, then ask for Pedialyte.

Today, I'm going to share a secret about that $15-a-litre wonder called Pedialyte: you can make it yourself almost free.

Take a litre of water and add six teaspoons of sugar and half a teaspoon of salt. Add some (as an option) pink colouring or bubble gum flavouring from a drink-mix powder and you have Pedialyte's equal.

The secret is in the sugar which gets absorbed by the small intestine very quickly.

And for every one glucose molecule that gets absorbed, 300 water molecules come along, too. The result is fast rehydration that tastes good to kids.

Now's a good time to mention that most soft drinks and sports drinks are not optimised to rehydrate you - they're optimised to sell well.

Most soft drinks contain high-fructose corn syrup, which is nowhere near as readily absorbed as glucose. Compared with Pedialyte, most so-called sports drinks have three times more sugar and half as much salt.

This is despite studies showing that such excessively high concentrations of sugars slow down water absorption.

Another case where it is better and cheaper to make it yourself.