ems sports nutrition: Nutrition rule 2

Hydration as a concept appears simple but is difficult to properly explain, and one of the most important things to get right - the body is far more sensitive to hydration than food. However, you can be dehydrated without being thirsty and vice versa - and drinking lots of plain bottled water is not necessarily the way forward.

The reason why hydration is so important is that water not only forms 60% of your body mass, but water a key role in your body processes on many levels - primarily:

As a solvent: the body uses water (via liver and kidneys) to wash away the by-products (e.g. lactic acid, ammonia, and other toxins).
As part of the energy cycle - Water saturated muscles burn energy more efficiently.
As a temperature regulator - e.g. through sweating.

Dehydration on the other hand has lots of nasty effects, first of all being dizziness, nausea, headaches, tiredness, irritability, sunken features (particularly the eyes), dry mouth and throat, and skin that becomes loose or flushed. Thus it is something to pay attention to whether you are exercising or not.

For the keen sportsmen reading – it is worth noting that one of the reasons on long training exercises your heart rate rises after 45 minutes or so is actually dehydration not tiredness. Even a small drop in body fluids and electrolytes can lead to a lower circulating blood volume. That makes your heart pump harder to maintain adequate blood flow to your vital organs and your body is less able to control blood pressure, distribute nutrients and eliminate waste.

How much should you drink?

The British Dietetic Association (BDA) recommends six to eight glasses of fluid a day, which is about 1.2 litres, as does the Food Standards Agency. However that 1.2 litres includes the water in your food and is an average figure based on the British climate and takes into account an average body volume. You will need more fluids if you are exercising (somewhere between 500ml and 1.0 litre per hour of exercise), or in a hot climate, or if you have a large body volume. Rough guideline as follows:

Weight		Training level/litres fluid
(Stone)	(Kg)	Low intensity	Medium	High
8st 3	52	2.2	2.3	2.4
8 st 9	57	2.2	2.4	2.6
10st 10	68	2.2	2.4	2.8
12st 7	80	2.3	2.5	3
14st 3	91	2.3	2.6	3.2

When should you drink?

The feeling of thirst is activated 1.) when the total body water level is reduced, and 2.) by low sodium levels. Even slight dehydration reduces the blood volume triggering thirst. But thirst is sensed only after dehydration is evident, or can be a counter indicator, making thirst a poor indicator that it's time to drink more water. One good rule of thumb is to pay attention to your lower lip - if its nice and full then you are properly hydrated, if its all puckered up then you are most likely dehydrated. Other is to check the colour of your urine, gross I know, but it should be the colour of straw (supplement effects aside) rather than the colour of Fanta, as one friend charmingly put it.

What should you drink

Plain water, especially bolted down rather than sipped, will go straight through you, and will not actually contribute to your body’s hydration. If you are consuming a great deal of plain water (upwards of 2 litres a day depending on activity level) then you are possibly creating a vicious circle (see below).

Ideally what you are looking for is something with a bit of sugar and a bit of salt, or sodium to be more precise. Sports drinks are ideal – but squash, tea (green, herbal or normal), coffee (caffeine issues accepted), diluted fruit juice (to avoid the blood sugar spike) will all do fine. None of this is to say that you shouldn’t drink plain water, especially when you are eating a meal which will provide the electrolytes for you – its just a question of what makes it easiest for your body to get hold of.

One last thing - taste and hardness aside – bottled water is a wheeze in most 1st world countries where the quality of public supply is often better controlled than bottled (need I remind you of the Coca Cola/Dasani/Thames-water-in-a-bottle fiasco http://www.timesonline.co.uk/article/0,,1-1023319,00.html). That said, for those of us living in London – the tap water does taste pretty foul.

Electrolytic level/Isotonic vs Hypotonic vs Hypertonic Sports Drinks

There are two key issues with drinking plain water, firstly its harder for your body to absorb, and secondly it actually dilutes the electrolytes (salts) in your body, diluting your body's fluids. If you drink too much water, two things will follow:

Firstly, drinking too much water will leads to increased urination, causing dehydration, then thirst, and round you go in a vicious circle.
Secondly, when excessive amounts of water have been consumed, your kidneys will not be able to eliminate all the excess water from your body, so the electrolyte/mineral content of your blood is diluted. This will firstly result in increased urination, but will also result in extreme circumstances in a condition called hyponatremia (low sodium levels - endurance athletes see below).

Isotonic drinks contain the same number of particles per kilogram as your blood and so are quickly absorbed, and carry electrolytes with the fluid – hence why it is what you should be on the look out for. Isotonic sports drinks (e.g. Lucozade Sport, Isostar, Powerade, Gatorade and, believe it or not, Sprite, SIS PSP22 http://www.scienceinsport.com/PSP22.htm ) are designed to replace carbohydrates as well as fluid and contain 5 - 8g sugar/100mls and a little added salt. You can make your own isotonic drink as follows:

a. Dissolve 60g glucose or sugar in 1 litre water or low calorie squash and add 1/5th teaspoon salt
b. Mix 500ml fruit juice and 500ml water and add 1/5th teaspoon salt
c. Mix 200ml fruit squash and 800ml water and add 1/5th teaspoon salt Hypotonic drinks (less than 3g carbohydrate per 100ml) also enhance water absorption but provide minimal energy.

These can also be used before, during and after exercise and may be useful if you are limiting your energy intake or have to drink very large amounts of fluid daily. e.g. Dexters, Lucozade Hydro Active, SIS Go http://www.scienceinsport.com/Go.htm)

Hypertonic drinks are more concentrated (more than 10g carbohydrate per 100ml). These drinks should not normally be drunk during exercise for although they will provide energy they will delay the absorption of fluid into your body and may contribute to dehydration. They can be useful for energy replacement after exercise, rather than fluid replacement. These have a place in particular if you have a high calorie intake requirement eg SIS PSP22 and Rego http://www.scienceinsport.com/rego1.html

Comment: I actually get along much better with Hypotonic rather than Isotonic, which I tend to find too sugary and at times make me nauseous. But then I’m always cutting weight rather than trying to maintain it so it’s a choice I can make, and that’s probably a very girlie comment. When you’re competing, you’re going to be better off with Isotonic drinks, and if you find the sugar too much, then wash your mouth out with plain water after drinking an Isotonic drink. If you’re training very hard, then you will need to use Isotonic when you are training, and Hypertonic straight after (or alternatively jam sandwiches will do the same job) to replace your glycogen stores to avoid the black hole of ‘glycogen depletion’ (eg you’ve run out of fuel, so dizziness, weakness, disorientation, never fun).

Hyponatreamia

A quick comment on Hyponatremia to finish up - this is a rare condition, where the sodium levels in your blood fall critically low, either through dilution or depletion. Most people would be sick before reaching it by dilution, but it is a risk for endurance athletes such as marathon, triathlon and iron man competitors who are exercising heavily over long periods. This particularly true on a hot day when athletes are also rapidly losing salt through sweat (e.g. Marathon de Sable competitors) - note in these circumstances this is a sodium concentration issue rather than a hydration issue. There's a couple articles at the bottom under the heading "hyponatremia" with some suggestions if you think this may be a problem for you. The jury is still out on the use of salt tablets – but it does seem to be a way forward if you suck them until the salt craving goes away. Complications have been linked to mono-sodium glutamate intake (or yeast extract – watch out for that one). This is really revolting stuff and it will make you feel foul even if you’re not exercising – so packet watch on anything that is (supposed) to taste meaty or savoury, or frankly, is mass produced.

Hydration Links

http://row2k.com/columns/index.cfm?action=read&ID=20

http://www.telegraph.co.uk/fashion/main.jhtml?xml=/fashion/2005/11/20/stjoshi20.xml

http://www.ft.com/cms/s/c3a1a262-1e18-11db-9877-0000779e2340.html

http://www.bda.uk.com/Downloads/FluidBalance.pdf