Isotonic drinks – what are they?

Every year I have the same problem with dehydration; I simply forget to drink enough. It doesn’t matter whether it’s a 200km bike ride (ridden on just 1.5litres) or just working in front of the computer – the same thing can happen easily enough, I forget to drink.

This lack of fluid can frequently lead to the most intense, head-splitting, agonising head-aches (I was once given an MRI scan as they thought there was possibly a brain haemorrhage happening!). They are horrific!

I try to remember to drink more, but over a period of a few days it can add up if I don’t keep up the routine. And sometimes when I do remember to drink I find that I’m drinking a diuretic drink anyway





adjective: diuretic

 (chiefly of drugs) causing increased passing of urine.

Both caffeine and sugar cause dehydration. Caffeine is a diuretic and causes an increase in urine volume. High concentration of sugar is drawing off water because your kidneys try to expel the excess sugar out of the blood. When you drink a caffeinated drink to quench your thirst, you will actually become thirstier.


I’ve been drinking Erdinger AlkoholFrei recently and wanted to take a closer look at what it proclaims to do to the body, in particular its isotonic nature.erdinger case

What is an Isotonic drink?  – Isotonic drinks have the same osmotic pressure as blood. Put simply, this means that the number of particles dissolved per liter of beverage is approximately the same as in blood plasma.

As a result, isotonic drinks can be absorbed into the blood particularly fast – handy for post-activity rehydration or simply to catch up if you’ve forgotten to drink that day….

I found it super interesting, and almost against what we tell kids, that water isn’t necessarily the best drink to have when we are dehydrated, water is absorbed passively into the blood, which as it suggests can be a relatively slow process, whereas the addition the of sodium and glucose can speed it up through active transport mechanisms (3-4 times faster!).

This meant for me that if I felt myself developing a migraine, then guzzling down a couple of litres of water may be long-term beneficial, but in the short-term it may not stop the migraine from developing in the first place, in this instance an isotonic drink may have a faster, more effective, reaction.

Isotonic drinks are particularly good for those who engage in endurance sports (activities that last longer than an hour), and whilst I wouldn’t carry a can of Erdinger in my water bottle on the bike, a tablet that can be dropped into the water can be handy for mineral replacement when out.

Those minerals are needed because we sweat them out as part of the body’s cooling system (sweat goes onto the skin, evaporates, and cools us down). However, that sweat contains salt and other good things – ever seen a salty cycling jersey after a hot day’s ride? – which the body needs, and insanely we can use up to 2.5 litres of liquid per hour during intense competition! This fluid loss causes the blood to thicken and, in-turn, makes it harder for the heart to work effectively (causing it to pump faster to compensate). And that’s why we are always told to drink more when exercising – and the reason why you see the pro’s out riding constantly taking sips from their bottles – this little and often approach both keeps the blood happy, but also doesn’t stress the digestive system.

According to research, a sodium intake of about 450 mg or more per hour of exercise is needed to maintain plasma volumes and plasma sodium levels. This amount can be easily achieved by beverages with a good balance of carbohydrates and electrolytes.

Now what is super fascinating is something that we see cyclists and other athletes engage in after a long rough race…the can of coke! Apart from not being good for you in general, it is not recommended that we compensate for a lack of fluids by drinking soft drinks such as coke after exercise, mainly due to them being hypertonic

“A hypertonic liquid has a higher concentration of solutes than blood plasma. It is only slowly absorbed as the liquid must first be diluted by the body. Soft drinks are therefore absorbed slowly and thus counterproductive with regard to fluid intake”

So why do they do it? almost certainly it’s that sugar kick, and probably to some degree, also a psychological benefit (even if there’s no real physical one)

Check out the coke stacks on the bottom left shelves.
Check out the coke stacks on the bottom left shelves.

On my trip to Team Sky one of the things that made me chuckle (obvs I didn’t mention it to them) was the big stack of coke bottles that they had on the shelves – so despite their attention to marginal gains etc(and if I recall, I think Sky have even gone so far as to say that they don’t drink Coke) the staff and riders still have ready access to it at the end of a stage (there’s also some research that caffeinated soft drinks in particular may even lead to mineral loss via urine when consumed after sports (Friedrich, 2009)).

This brings me back to Erdinger Alkoholfrei, pitched as an isotonic thirst quencher for athletes, made without chemical additives and brewed within strict Bavarian purity laws, Its combination of ingredients and their qualities make it a solid choice for a recovery drink. Its isotonic qualities put it smack in the middle of the isotonic range (Drinks between 246-334 mosmol/l (= 290 mosmol/l +/- 15%) are referred to as isotonic. Drinks which are significantly lower than 245 mosmol/l are referred to as hypotonic, while those significantly above 335 mmol/kg are referred to as hypertonic  – Erdinger comes in at 289mmol/kg).

We all know it’s important to stay hydrated, especially if you are engaging in sport or physical activity, and whilst water will do a great job at keeping you hydrated during exercise, an isotonic drink will certainly do a better job post-exercise, with the addition of minerals and glucose ensuring that the recovery process is kick-started as rapidly as possible. Wifey is always super skeptical of sports drinks and their ilk, however after reading the label on the side of the bottle, she was not only happy for me to drink it, but she was also keen to quaff it after her own runs – this is pretty major in our house as she literally doesn’t believe in sports drinks, refusing to take a recovery drink even after doing a 30k run!

What I found of interest from reading and preparing this post was the difference in absorption rates of fluids, so that some are better for rehydrating than others – this is obviously important for me when trying to stave off migraines! erd test

In the spirit of full disclosure, Erdinger have sent me a crate of Erdinger Alkoholfrei in the past, however no money has exchanged hands for writing this.

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