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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

TRANSCRIPT

 

7 Nutrition Tips for Exercising in the Heat

 

Good morning and welcome! This morning I want to talk to you about my tips for exercising in the heat because I'm deep in the middle of writing nutrition plans for the Cairns Ironman Race Nutrition Plans and there's a bunch of people competing. There’s a few nutritional strategies that are really important if you're trying to exercise in the heat. I really want to share some of those with you.

This is definitely for all the Cairns Ironman or 70.3 athletes. But also just generally, if you're exercising in the heat, like here in sunny Brisbane, all of these strategies can come into play for you as well. As we head into winter, it's not as useful, but I think for those heading to Cairns doing the Ironman, this would be super important for you. Particularly, because it's so much cooler down here.

I'm in Brisbane at the moment and our average temperatures are around 10°C to 23°C maximum throughout the day and our humidity is only about 50%. If you're down in Melbourne, I've got a couple of clients in the Melbourne region heading up to do Cairns, it's even colder there around 9°C. Going from a cool environment to a hot environment, that's something to really consider because Cairns is going to be hot. Their temperature averages at the moment are minimums of 20s and up to 30°C in the day, but the humidity is quite high. So you come out of the airport and the heat just smacks you in the face. It's really important to understand that, if you've not been up there and done the race before, and if you have, you know exactly what I'm talking about.

The humidity is also really high up there too and ranges from 60 to 85%, depending on what the temperature is. As the temperature is cooler in the morning, the humidity is higher and as the temperature of the day arises, the humidity drops. So having that in the back of your mind for your race as well. In the morning, it would be cooler, but the humidity is much higher and as the day heats up, the humidity drops. It's understanding what your hydration needs are through that temperature range as well. Keep in mind that you're going from a cooler environment to a hot one. It’s really important to do a few things heading into the race to make sure you set yourself up for success.

 

What happens to the gastrointestinal tract (GIT)?

One of the biggest impacts of heat exposure, when you exercise, is its effects on the gut. We know that it's exacerbated by core temperatures that are greater than 39°C. Any of your nutritional strategies to manage that heat will evolve around trying to keep that core temperature below 39°C. We'll talk through some of those later. Before I get into some of the practical stuff, I want to talk you through what actually happens. I think that's really important to understand – what is actually happening to your body in the heat so that your nutritional strategies and what you do, are designed to set up minimizing the impact of that.

When our body heats up and we’re exercising in a hot environment, blood flow redistributes from your gut into your working muscles. That happens with exercise usually anyway. It goes towards the working muscles and your peripheral circulation to try and cool you down. That means that there's less blood flow, less perfusion of all the organs in your abdominal cavity and that is called Gut Ischemia, lack of oxygen. Things aren't working properly when you're exercising in the heat. As well, with exercise, you have activation of the sympathetic nervous system, the fight or flight response. We don't really want to be digesting when we're running away from a lion, right? It spends too much energy doing that.

You've got all these things working against you to try and absorb nutrition when you're exercising and then throw heat at it and it exacerbates that as well.  Then that also suppresses your gut emptying. The stomach doesn't empty as efficiently as it should, and it doesn't digest and absorb as well as it normally does as well. All that happens with exercise and the longer you go for and the more intense it is, the worse it is. The Ironman is tick, tick, tick for all those things. Throw heat at it and it makes all that worse. You need to understand that when you go to exercise in the heat, that what you would do in a cooler environment may just not work in a hot environment.

We know in the heat, you rely much more on muscle glycogen. That's the carbohydrate you store in the muscles. It's right there where you need it as a fuel source. You rely more on the anaerobic metabolism. That's the metabolism where there's less oxygen available, right? It's usually the high intensity huffy puffy sessions where there's not a lot of oxygen available to have a conversation and that draws on much more muscle glycogen. We need oxygen to oxidize fat. The long slow diesel engine type Ironman stuff, if you're a slower athlete, then you're doing a lot of fat-burning through that. In the heat, it flips your reliance to carbohydrate more so than if you were doing it in a cooler environment.

I know a lot of people struggle in the heat. If you did Port Macquarie, which got cancelled, you might have a better race outcome than compared to doing Ironman in the heat and these are the reasons why. I wanted to explain a bit of the nerdy science background behind it because I love it. It also helps you to understand why you do some of the things you do when you then flip to exercising in the heat.

Now, I'm just going to throw this caveat out there. It's too late to do race nutrition overhauls right now. The tips I'm going to give you, take them or leave them. I've tried to keep them relatively general and you'll see in a second what I mean. I've started to see a couple of Ironman athletes come through in the last couple of weeks and it's almost too late to be doing the nutritional interventions that I would be doing if I started working with them 20 weeks ago. Usually with an Ironman athlete, I will work with them five, six months out because I want to build your gut tolerance to nutrition right through that training block. As your training volume increases, I do all of my nutrition interventions to do that. You really need to train your gut to absorb more carbohydrate when you do an Ironman and then particularly for Ironman’s in the heat. Like I said, you're using more muscle glycogen, so we need to carbohydrate load to make sure that there's plenty in storage, more than you would normally have. That requires a bit of systematic increase in carbohydrate intake. It doesn't mean you guts yourself. You want to do it strategically and planned and practice that as well. So they're the kind of things that you can do when you start working with a sports dietitian.

Alright, let's go through this. I've got 7 nutritional strategies to manage exercise in the heat from a nutrition perspective.

 

Tip 1 - Heat Acclimation

So the number 1 thing that you can do, if you go into a hot environment, is some heat acclimation. Now that's exposure to the hot temperature over a 7 to 14 day period. They think around 10 to 14 days is optimal. I know a lot of you are just coming into Cairns a couple of days before. So it really just depends if that's practical and feasible with work and paying for accommodation and all that sort of stuff. But there's some things you could do at home to heat acclimatise.

What it actually does is, it helps to expand your plasma volume, so it enhances your fluid balance. It also reduces your heart rate so that you've got a decreased rate of perceived exertion in the heat. When you go to a hot environment, you obviously sweat more, right? You should notice that when you go to Cairns, you'll start increasing your sweat rate. That's the body trying to adapt, but interestingly, the body is so smart. It actually increases the sweat rate, but the sweat sodium concentration decreases and it’s the body’s way to kind of conserve your sodium. Even though you're sweating more, your sweat sodium is actually lower following heat acclimation or about the same. It's not more so it makes absolutely no sense to start sucking back sports drinks and trying to salt load like the week heading into Cairns. Please don't do that. If you take nothing away from this, other than that, I'll be happy. I'm so sick of hearing people talking about salt loading when they go into a hot environment. You’re just absolutely destroying your kidney’s natural ability to adjust. You’re overriding that adjustment. If you increase your sodium too early, you're just going to increase the kidneys filtration of sodium. It's just going to make the whole thing worse. Please don't do that. Do another one of the tips that I'll talk through later if you want to do a bit of sodium loading.

If you're here in Brisbane or Melbourne or somewhere that's cooler, you can do some hot temperature exposure. You can do some of your wind trainer sessions over the next couple of weeks at home and crank the heat. Get yourself in the laundry or a bathroom so it's a small environment. Turn the heater on and do some of your sessions in a hot environment, if you don't have access to heat chambers or any of that sort of stuff. Even getting in a sauna is heat exposure to get the body used to being hot again. Particularly, if you're down South and it's a maximum of 9°C. Your body needs to understand what hot feels like again.

Just be mindful that there is, what's thought to be a rate of decay of around 2.5% for each day that you're not exposed to heat. Even athletes that might do a heat exposure block for two weeks and then leave the heat because of travel, there is a bit of a decay. Depending on how long that the days of non-exposure are, that 2.5% can build. That's pretty interesting as well. Ideal scenario, if you're a pro athlete and you've got all the time in the world and you don't have kids and you don't have a job, go to Cairns early. Go a couple of weeks early and acclimatise to the heat and do your last sessions in the heat, and then you'll adapt. You'll increase your plasma volume and you'll be better able to handle that exercise load in the heat. That's my number one tip. It is not necessarily practical for some people but good bang for buck.

 

Tip 2 - Drink a sodium-containing sports drink

Now my tip number two is to make sure you drink sodium containing sports drinks during your race. You have better plasma volume retention if you do that because sports drinks were actually designed to drive thirst. The sodium level in them was designed to drive thirst. So if you're planning on drinking on the bike, then that actually drives thirst and it increases your ad libitum intake of fluid. That means you will drink more just naturally because you feel like you should be doing it.

I've seen a client recently who wasn't using sports drink on the bike. He was just doing gels for the entire five and a bit hour bike ride. The type of gel he was using only had about 13.7 milligrams of sodium in each gel. So I calculated how much that would be across the whole bike leg. He's having 3 gels an hour x 5 hours. That's 15 gels. So the total amount of sodium in that is 205 milligrams for an entire bike leg and that was it. It was that and water. In a hot race, you're going to be sweating and you will be losing sodium. 205mg across an entire bike leg is nowhere near enough in terms of sodium replacement.  I'll try and talk about the science behind that too. That's a deep one. It's not going to help drive his thirst either so he's less likely to drink what he needs without that sodium intake.

A 600ml bottle of Gatorade, I think Lemon Lime is the flavour that's available on course this year, that's got 336mg of sodium per a 600ml ready to drink bottle. Already just one bottle of sports drink has more sodium than the gels. What I've asked him to try is introducing a sports drink on the bike so that his sodium intake from fluids alone is around 3,660mg of sodium on the bike now. That's 17 times more than what he was planning on doing. That doesn't include some of the top secret strategies that I'm working on with him as well.

Remember to look at sports drinks as an opportunity to help you drink in the heat. They help drive thirst. There's some really cool studies. There's one particular good study in Ironman athletes where they either didn't hydrate them to certain percentages of body weight, they let them drink ad libitum so drinking to thirst, drinking what you feel like you need, and then did some other specific you need to drink this many mL’s an hour for a few different levels of percentage of dehydration. They found that the athletes that drunk ad libitum, so what they felt they need and then also the planned rates did better performance wise than the people that got too dehydrated. But interestingly, the people that had enough fluid intake to make sure their dehydration didn't hit more than sort of 2% didn't really do any better than the people that just drank ad libitum.

So if you've got a sports drink on the bike and that's helping you to drink and drive thirst, then that's a much better strategy sometimes than giving you a set target of mL’s per hour to get. Unless you've done your own sweat and hydration testing and know exactly what your individual needs are.

How much sodium do you need?

How much sodium you need really depends on you. It depends on how you sweat, your sweat rate. The highest driver of sweat sodium is just sweat rate. The more you sweat, the more sodium you lose. Remember your body will naturally adapt in a hot environment and reserve a bit of sodium if your sweat rate increases. You don't necessarily have to take salt tablets. That was one of the questions I was asked. There's unclear evidence around sodium replacement guidelines. I think the answer to that question is really highly individual. You need to put sodium in to replace your individual losses, and you're not looking at replacing a hundred percent anyway.

You'd need to look at doing sweat testing with a qualified sweat tester while you're exercising, not sitting down. You need to do it while you're exercising in a similar environment to what Cairns is. Do it in our Summer if you're looking at doing Cairns again next year. Get an understanding of what your sweat rate is and what your sweat sodium concentration is as well so that you can have a bit of a plan for that rather than just going “I'm just going to have one salt tablet an hour because that’s what the packet says”.

That's another side note, with all these products. This guy was doing gels. He was doing three an hour because the packet says, “Take one every 20 minutes.” Now that's marketing, right? That is designed to make you buy more of their product. Work with a sports dietitian to figure out what your actual overall plan is. That product is not ideal for him and it's not enough sodium for him for an Ironman in a hot environment either. Be mindful about what the packet says. It doesn't necessarily mean that it's an evidence-based guideline or what you should be doing, and it also needs to fit in with your overall plan too. It's just designed to make you buy more of their product.  

 

Tip 3 - Keep pace with your sweat losses

My tip 3 is keep pace with your sweat losses. It's highly individual how much you sweat. There's no point drinking a set amount of volume per hour, unless you know what your sweat rate is. Don't listen to somebody that says, “Oh, you need to drink this much an hour.” That could be purely based on what their sweat rate is. You need to understand what your sweating style is, whether you're a heavy or a normal sort of sweater, and then keep pace with those sweat losses.

We talk about performance being affected negatively when dehydration exceeds more than 2% of body weight. With endurance stuff, a bigger percent might be okay. Some of these people in this Ironman study lost like 3% body weight and were still performing better than people that were dehydrated. Even up to maybe 4 or 5%, it's really highly individual. You need to understand what your sweat rate is and then keep pace with that so that you're not getting to the point where you’re too dehydrated where performance is starting to be affected.

On the flipside of that, it's unlikely to happen in Cairns, but you can over-drink as well and get something that's called hypernatremia where you’ve got low sodium levels in your blood and that's really bad. It can be life-threatening. That's more likely to happen in a cooler environment for a slower athlete, somebody that's maybe walking through aid stations and drinking lots at aid stations and then their pace is not that fast as well. Slower athletes, more opportunity to drink, that’s more likely to happen rather than the faster athlete to grabbing a cup of water at an aid station but flying through, and most of it's going over their face. You can over-drink as well and just be mindful of that, but it’s unlikely to happen in a hot environment like Cairns, but more likely at Port Mac where it's cooler.

 

Tip 4 - Keep your fluids cool – internal cooling

Number 4, this is something that I think you can do without much practice, is keep your fluids cool. That will help with the internal cooling, keeping your core temperature below 39°C, if you can. We know that fluids less than 22°C increase the palatability so you're more likely to drink them if they're cool. Anything less than 10°C is going to have extra benefit because it will help with that internal cooling. The struggle with that though, is that it's unlikely that you'll be able to have fluids that are less than 10°C at Cairns.

What I would suggest is that you freeze your bike bottles overnight because you can go to transition in the morning and pop them on your bike. They might be a bit cool for the start of the bike leg before they melt, but at least you're starting with cold liquids.

The other thing that you can do to keep your liquids cool on the run is, if you've got a flask that you're going to carry, try and put some ice cubes into it as you are going. Grab some as you run past or if you're walking through aid stations, whatever you're doing, try and put a couple of cubes in your flask and keep that water in your hand cool. Try and put it on your hip or somewhere so that you're not been warming up in your hands. A couple of strategies there to keep your fluids cool, which you can do now. There’s no harm in implementing that strategy, so that's another good takeaway from today.

To also keep your body temperature down, you can try putting ice on you. Put it on your chest, put it in the back of your suit, try and keep ice on you to keep you cool. Performance is affected when your core temperature gets above 39°C and your guts going to work better if it's below 39°C. On the run where there's ice available, chuck it in your top, chuck it wherever, in your undies, wherever you want to put it, put it on your forehead, just try and do something to keep yourself cool in that hot environment.

The next couple of strategies are not something I would play with unless you have got specific advice. This is something that I do with my athletes, but I get them to practice, and we know well ahead of time what their plan is so that they are practicing it and it feels okay and there's no adverse effects.

 

Tip 5 - Acute sodium loading

Number 5 of my strategies is some acute sodium loading. Before, I told you that you don't need to salt load early, please don't. As you go from a cold to a hot environment, you actually screw things up worse by doing that. But you can do some acute sodium loading and that's what you would do in your pre-race breakfast.

1 to 2 hours before the start… it is highly individual, and I calculate plans specifically for you, everyone’s is different. I'm not going to tell you how to do it in this forum because I don't want you doing it without help. Sodium loading is definitely something that you can do to help increase that plasma volume and help you retain that fluid the morning of the race so that you are maximally hydrated.

What you can do though is just make sure you're super, well-hydrated heading into the race. Making sure you're keeping up with the increased sweat loss as you head up to Cairns. Waking up in the mornings, your pee colours are nice sort of pale straw colour rather than really dark. You want to wake up race morning and have straw-coloured urine rather than really, really dark. Keeping pace with those sweat losses, it's something you can do without help.

If you want a pre-race breakfast, acute sodium loading plan developed, I'm happy to do it. If we do it in the next week or two, just send me a message and book in for a consult. I'll get you to practice that as well. We've got a bit of time to do that strategy. If you want to, but don’t go at that alone.

 

Tip 6 - Acute sodium loading + glycerol

The other one that you can do is adding glycerol to that sodium load. Glycerol is a 3-carbon alcohol. It was actually taken off the WADA banned list in 2018. It's going to assist with fluid retention before you race as well. It expands your plasma volume and decreases urine output, but it's not something that you would do on your own either.

I would try the acute sodium loading first before adding glycerol because glycerol is kind of like, if you've been here for a while, you know that I have a foundational nutrition model, and glycerol is kind of the sprinkles on the icing on the cake. You wouldn't implement that without doing a bunch of other things first.

 

Tip 7 - Menthol - NOT ONE TO MESS WITH

My 7th strategy, which is, again, the sprinkles on the icing on the cake is playing with your thermal sensation in your mouth and using things like menthol for that. It activates your oropharyngeal receptors. You know, how you have mint or mentos or gum and it has that cooling sort of effect the mouth, that increases your threshold temperatures for the activation, and it creates a feeling of coolness.

So definitely sprinkles on the icing on the cake, menthol and if you're going to do it, definitely don't mix up your own menthol concoction because it can be fatal with the risk of toxicity of that. There are commercial products available. My 7th strategy is definitely sprinkles on the icing on the cake.

 

So that is 7 ways that you can manage exercising in the heat. I think there's some really practical take homes from that, like freezing your bottles, trying to get ice on your body and in any flask that you're carrying on a run just to keep yourself cool. Keeping on top of your hydration as you head into the race, maybe some acute sodium loading if you're working with a sports dietitian which is going to be beneficial. Please, please, please don't start increasing your sodium intake when you go up there for the race. You're just messing with your kidneys natural ability to figure itself out. I hope that's helped.

I'll send out this as a replay in an email later on today. One thing I didn't touch on is cramping because it is a whole another topic of conversation. I can talk about it for hours. In the heat where you're likely to sweat more, cramping can be a factor. It is multifactorial though so it's definitely dehydration. It's not necessarily sodium replacement cramping. Magnesium doesn't have a lot of evidence behind it either. Sometimes in Ironman, I don't know if there is any available in Cairns, they've got this pickle juice shots and that's got some evidence behind it as well, like the cramp fix type things.

 

Cramping is a whole another topic of conversation for another day. In 20 minutes I can't cover that. Even exercising in the heat, I'm pretty sure I've gone over. It's too hard to cover in 20 minutes but feel free to watch back the replay. I'll pop the email out later on today. 7 strategies to try and help you with exercising in the heat and hopefully some good take homes that you can implement for your race in Cairns if you’re doing it. All right. I might sign out, but thanks for joining me and I'll see you next week!

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