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Running in the Heat – Hydration and Nutrition basics

Running in the Heat – Hydration and Nutrition basics

What to eat and drink when humidity is all around

This information is paraphrased from an article written by Rin Cobb, a Sports Dietitian specialising in endurance nutrition and published on the UK-based RunUltra website. Rin provides valuable insights into dealing with nutrition and hydration when training or competing in hot weather, particularly hot, humid weather such as we experience in coastal regions each summer. Do you know how to estimate your sweat loss?
Heat and humidity combined may not only affect your running performance but your health too through varying degrees of heat illness including heat exhaustion, exertional heat stroke, heat cramps and heat syncope (fainting). Unsurprisingly, both dehydration and hyperthermia are the key culprits. Eating and drinking adequately makes the difference.
There is no one size fits all recommendation with regards to how much you should drink when exercising so you need to try and work out what your own body needs under different conditions. Some of you may already estimate your own sweat rate but if not here’s how to go about it:
Estimating fluid loss/sweat rate:

  • Weigh yourself after emptying bladder just before going for a run
  • Weigh yourself after emptying bladder when you finish
  • Difference in weight plus any fluid drunk during run

Example: 0.5kg loss in 1hr run + 500ml fluid intake = 1kg/L sweat loss/hour
If you can work out what your fluid losses are then this will give you a guide to how much you need to replace per hour. Additionally it can also help you work out how much to drink after you’ve finished a run, which when you have a limited amount of time to recover and replace fluids should be 1.5 times your losses to account for regular toilet trips.
A more crude, less practical way to see if you’re well hydrated during a race, is to check the colour of your pee. The lighter it is, the better hydrated you are and aiming for straw-coloured pee is desirable.
While there are several strategies for maintaining hydration during exercise it is advisable to try to drink little and often as the gut can struggle to absorb and use large volumes of water in one go.
Sodium is the main electrolyte lost through sweat, whilst potassium, magnesium and chloride are lost in much smaller quantities. You’ll generally find sodium added to sports drinks ans electrolyte tablets but this isn’t only to replace losses but also helps the gut absorb fluid better and can make you feel more thirsty, thus encouraging you to drink more. (here we inject a note of caution to Rin’s information; over-hydration (Hyponatremia) is often considered medically to be more dangerous to your health than dehydration, so it is important to monitor your sodium intake carefully. We will provide more on the symptoms and dangers of hyponatremia in a seperate post so please keep watching for new articles).
As the temperature rises, so will your bodies use of carbs for fuel. Even for a catered race or long training session taking some carby snacks, which you’ve tried and tested is a good idea.
Using sports drink powders with added electrolytes is a practical all in one option which provides carbs for fuel, fluid to rehydrate and electrolytes to replace losses and help your body absorb the fluid better; et voila! Just be sure to check powders have enough sodium if not using additional electrolyte products with the optimal amount being 0.23 – 0.58g sodium per litre or 0.57 – 1.45g salt per litre.

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