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7 Nutrition Tips for Exercising in the Heat

May 13, 2021
 

With Cairns Ironman just around the corner, I’m deep into writing race nutrition plans for our athletes. This morning on Coffee & Questions I wanted to share with you some strategies to assist with training and racing in the heat.

One of the biggest impacts of heat exposure when exercising is its effects on the gut. This is exacerbated when our core temperature gets >39°C

 

What happens to the gastrointestinal tract (GIT)?

  • Redistribution of blood flow away from the GIT towards working muscles and peripheral circulation
  • Results in decreased perfusion of organs in the abdominal cavity causing GIT ischemia (lack of oxygen)
  • PLUS sympathetic activation – fight or flight response – you don’t want to spend energy digesting food when you’re trying to run away from a lion
  • Suppressed gastric emptying, digestion and absorption

 

All of this happens with exercise – the longer and more intense – the worse it is. And it is exacerbated by heat exposure

  • We rely more heavily on muscle glycogen in the heat – reliance on anaerobic metabolism where less oxygen is available
  • Higher carbohydrate needs

 

So what do we do about it?

 

Here are my 7 strategies to manage exercise in the heat (from a nutrition perspective)

 

1. Heat acclimation

Exposure to hot over 7-14 day period. 10-14 days optimal
Expands plasma volume – enhanced fluid balance – reduced HR – decreased rate of perceived exertion

Increased sweat rate – but interestingly sweat [sodium] decreases to conserve

Sweat sodium loss is the same or lower following acclimation

 

IT MAKES NO SENSE to start sucking back heaps of sports drink when you head north

All you’re doing is messing up your body’s natural adjustment

Increase sodium too early, increase filtration in the kidneys

Rate of decay ~2.5% per day without heat exposure

 

2. Drink a sodium-containing sports drink

Better PV retention
Sports drink was originally designed to drives thirst – increases ad libitum fluid intake

  

Reminder – don't simply do what a packet tells you to – generally it's marketing designed to help you buy more of their product or stick with their brand

Seek professional advice when it comes to training and racing nutrition to find a holistic plan that's practical and evidence-based.

 

HOW MUCH SODIUM do you need?

It depends – you need to understand how you sweat.

You shouldn’t just take salt tablets because your training buddy told you to

Develop an Individualised protocol based on your sweat testing results in the same environmental conditions

If you're interested in doing sweat testing, learn more about how it works and when our next session is HERE

 

3. Keep pace with your sweat losses 

  • Highly individual
  • Do sweat testing to understand how you sweat, build your gut tolerance to meet your needs
  • Prevent dehydration to the point where performance is affected
  • Don’t OVERDRINK – risk of hyponatraemia (low sodium)

 

4. Keep your fluids cool – internal cooling

<22°C will increase palatability – you’re more likely to consume

<10°C – additional benefit but NOT LIKELY TO BE PRACTICALLY POSSIBLE IN CAIRNS (without outside help)

  • Freeze water bottles overnight
  • Add ice to your flasks as you run
  • PLUS chuck ice down your top for an external cooling strategy

 

5. Acute sodium loading

There is no benefit in salt loading for multiple days before when you go to a hot environment

There is a benefit to acute loading – 1-2hrs prior to the race start

Highly individual – I’m not going to tell you how to do it in this forum as it’s not something to mess with

If you want an evidence-based plan specific to you – you can book a consultation with me HERE

  

6. Acute sodium loading + glycerol

3-carbon alcohol taken off the WADA banned list in 2018

Assist with fluid retention pre-event – expands PV and decreases urine output

This is a sprinkles on the icing on the cake strategy - nail all of the others above first before doing this one with a professional qualified to give you the right advice

 

7. Menthol - NOT ONE TO MESS WITH 

Alters thermal sensation in the mouth

Activates oropharyngeal cold receptors – increases the threshold temperature for their activation – creates a feeling of coolness

DEFINITELY – test first

Use commercial products – risk for toxicity

 

Again, this is a sprinkles on the icing on the cake strategy – there are 5 strategies listed above to trial before you would even consider this one!

 

If you want help putting into practice any of the strategies above, or are looking for a Sports Dietitian to help you with training and racing nutrition, learn how you can work with me HERE

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