7 Nutrition Tips for Exercising in the Heat
Nov 11, 2021
It’s getting hot here in Australia! Training in the Aussie summer can be challenging.
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) when we exercise?
- Redistribution of blood flow away from the GIT towards working muscles and peripheral circulation (to cool you down)
- Results in decreased perfusion (less blood flow) of organs in the abdominal cavity causing GIT ischemia (lack of oxygen)
- 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
- Supressed gastric emptying (less efficient compared to normal), digestion and absorption
The longer & more intense the exercise, the worse these responses are.
Here are 7 strategies to manage exercise in the heat from a nutrition perspective:
1. Heat Acclimation
- Exposure to a hot environment over a 7 to 14-day period
- Expands plasma volume, enhances our fluid balance and reduces our heart rate so that we have a decreased rate of perceived exertion in the heat
- In a hotter environment, we sweat more. Interestingly, sweat sodium concentration decreases to conserve sodium
- It’s not necessary to overload on sports drink/salt tablets as this messes up your body’s natural ability to adjust
- Rate of decay once heat acclimatised of 2.5% per day without heat exposure
- Ideal situation = go to a hot race early and adapt to the conditions 2 weeks before your race
2. Drink a sodium-containing sports drink
3. Keep pace with your sweat losses
- Sweat rates are highly individual and range from 400-500ml/hour to 3-3.5L/hour
- Keep pace to prevent dehydration of no more than 2% body weight where performance can be negatively impacted. For ultra-endurance events, this percentage may be higher
- It’s not necessary to replace 100% of sweat losses
- Over drinking can lead to hyponatremia (low sodium) which can be fatal
4. Keep your fluids cool – internal cooling
- Helps to keep our core temperature down below 39°C
- Fluids that are less than 22°C will increase their palatability
- Fluids less than 10°C have additional benefits with internal cooling
- Practically, it can be difficult to keep fluids cold. Try freezing your bottles overnight and adding ice to your run flasks when available
The following 3 strategies require professional assistance to avoid adverse effects
(i.e. don’t try this yourself at home!)
5. Acute sodium loading
- There is no benefit in sodium loading for multiple days before arriving a hot environment.
- But there is a benefit to acute sodium loading in the 1-2 hours before race start
- If you want an evidence-based plan that's specific for you then book in for a consultation
6. Acute sodium loading + glycerol
- Glycerol was removed from the WADA banned list in 2018
- It assists with fluid retention by expanding plasma volume and decreasing urine output
- Alters thermal sensation in our mouth by activating our oral pharyngeal cold receptors
- Creates a feeling of coolness
- Use a commercial product – don’t mix your own! Risk of toxicity and can be fatal
They are my seven nutrition tips for exercising in the heat. I hope that there are some really practical take-homes for you, including making sure you understand your individual sweat needs, particularly in a hot environment. Keeping your fluids cool, whether that's freezing bottles or putting ice in your flask while you're running. Making sure you keep on top of your hydration heading into your race. Using some sports performance strategies like acute sodium loading to help with managing your hydration before you even start the race.
If you are interested in getting an understanding of YOUR sweat needs, book in for a sweat test. Head to www.dietitianapproved.com/sweattesting
To go deeper, listen to the Triathlon Nutrition Academy Podcast Episode 16: ‘7 Nutrition Tips for Exercising in the Heat for more!
Listen in wherever you listen to your podcasts 🎧