Nutrition and Hydration Basics for Ultrarunners
A word of caution before we get into it: nutrition and hydration is extremely personal. The best way to know what/how often you should eat and drink is to test things out during your longer training runs and see what works for you. While I give some numbers and suggestions here, know most of this is genetic, so test, test, test!
One of the unique aspects of ultras is the necessity to take in a large amount of calories while running. In a marathon, you may be able to get away with a few gels. But for an ultra, you may be out for 5-24+ hours! Eating and hydrating properly is a must.
You’ve probably heard of “bonking” - that feeling when you suddenly ‘run out of gas’ in a longer run. What gives? The slightly more scientific way to describe what’s happening is: your body has run out of carbs to burn for fuel, which means it has to resort to fat, which takes longer to turn into fuel (this forces you to slow down). Carbs are important because they provide the faster energy we need to fuel a run. ⚡
Some education on carbs as fuel
Our body is always burning some combination of carbs of fat for fuel - a “fat burning” workout is a bit of a misnomer because of this. But the % of carbs you’re using vs fat depends on how hard you’re working. Why is this? Carbs are faster (more readily available) fuel: it takes longer for your body to extract the energy it needs from fat, so if you’re working at a higher intensity and your body needs energy ASAP, it will resort to carbs for its primary fuel source. This is important to know, because it ultimately factors into your nutrition equation: how many carbs you should consume per hour depends on how hard you’re working.
Keep in mind you do not have to replace 100% of the calories you burn. Especially for ultras when you should be operating in zone 2, you’re likely leaning to using more fat as fuel than carbs (though this is also very genetic and varies person to person).
One other thing to consider when it comes to carb strategy is your glycogen stores. Glycogen stores are stored energy from previous meals, and most of us store around 1,000-1,200(ish) kcal’s total. One note on this: You cannot ‘carb load’ beyond your glycogen storage capacity: important to keep in mind for that pre-race meal. What happens when you can’t store something? …Exactly. 💩
Let’s do some math!
To make calorie/carb planning easy you can look at a long training run you did: look at your average heart rate (HR) and calories burned. Let’s say you ran 20 miles and burned 4,000 kcal in 4 hours, and your avg HR was 143 the entire run. Let’s say that’s a good HR and comfy pace, and you’d like to hold that for your ultra. That means you’re burning 1,000 kcal per hour. You do not need to consume 1,000 calories per hour, since some % is coming from fat (and that HR is likely below the midpoint of that graph linked above, give or take). So, you really only need to replace some % of your calories burned after you’ve gone through your glycogen stores. Carbs are 4 cal/g, so that’s 125 g of carbs an hour lost if you were burning 50/50 carbs/fat. 1 gel is usually about 30g of carbs and 100 calories, so you can see how important your food consumption becomes, and where ‘bonking’ comes from! This actually ties into your pacing strategy too, and why it’s so important to keep your HR controlled. Consuming 125g of carbs/hour takes some getting used to for most people to avoid digestive issues, so you want to keep your HR in that green zone above to avoid bonking and tummy upset.
For me, a 110 lb female, on a normal training run when I’m out for more than an hour I shoot to consume around 40g of carbs/hour (or 2 gels/200 calories) and I find this works well for me, assuming I’m going out for an easy run in lower HR zone. If I’m racing something shorter like a 25k or marathon, I know my HR will be higher so I increase carb consumption. Note: I sit on the low end of what’s typical but I find it works well for me: I have never had tummy upset during an ultra!
Top tips for nutrition
I strongly suggest you test any planned race-day nutrition during long training runs. And do multiple tests with a variety of options.
Try gels vs real food vs liquid calories (powders) to see what you enjoy the most (and tolerate best!). I personally enjoy eating *real food* as long as I possibly can (think bars, cookies, muffins, pretzels, sandwiches, etc).
Always pack a variety of both sweet AND salty foods and your pallet will change during the race. One will likely become more tiring than the other.
While you can certainly rely on aid stations to supplement your food I always suggest carrying as much as you can to be self-sufficient. Aid stations may run out of the food you had a taste for, etc. I like to think of aid stations as a bonus for that extra 100-150 calories I could use, not my primary fuel source.
Next topic, hydration!
First let me say, everybody’s sweat rate varies, and also varies with temperature changes: there is no perfect formula for what you need to consume. As above, it’s best you test things out during training runs at various temperatures to see how your needs change.To give you a baseline to start from, in general, it’s a good idea to drink approximately 0.5 L of water/hr. On cooler days, I can personally get away with a bit less, on hotter days it might be closer to 1L. This is something that’s very important to test, and test with electrolytes. A word of caution on this: just like consuming too many calories has consequences, drinking too much water can, too. In fact, much more serious consequences. Hyponatremia is a serious condition that occurs with excess fluid intake (your body holds too much water). If you start to notice symptoms of hyponatremia such as headache, nausea, fatigue be sure to seek medical attention immediately.
So let’s talk about how to prevent such things: one way is to ensure your electrolytes stay in balance.
Why do we need electrolytes, you ask?
Electrolytes help regulate fluids in our bodies: they’re essential nutrients for all bodily functions, and also help regulate our nerve and muscle function. Get your electrolyte balance ‘off’ (too high or too low) during an ultra and it can be very hard to get back in line, not to mention downright dangerous if you do it wrong. There are also some general numbers (which again, vary person-to-person), but most people lose between 700-1500+ mg per liter of sweat.
Important note: you’re not just sweating out sodium! It’s important to replace other electrolytes like potassium, magnesium, etc to preserve muscle and nerve function. The good news is, most off-the-shelf electrolyte supplements nowadays have you covered with a mix of sodium, magnesium etc.
If you're curious about how many electrolytes you need, the Nix Biosensor is a great tool to measure this! It's about $120,, a wearable that comes with disposable patches so you can test your sweat rate and electrolyte concentration over a few runs (it has an app as well)
I always carry salt pills, but prefer to mix-in electrolytes with one of my water bottles as taking salt pills makes you *very* thirsty: this can make you get out of whack (take salt pill, get very thirsty, drink too much water, take another salt pill...you get it!). If the electrolyte is mixed in with the liquid you won't have that issue. LMNT is great, and I usually put 1/2 pack per water bottle (500mg), as I'm usually eating some salty foods as well throughout the course of an hour.
Always be mindful that you’re also getting some sodium in through snacks. You don’t want to overdo it on the electrolytes either as recent studies have shown that you can also put yourself into hyponatremia by taking in too much (too much sodium will make you thirsty, which causes you to drink more: our bodies will excrete the excess sodium but not the water).
As you can see, hydration and electrolytes are very tricky to get right. David Roche, a coach and pro ultrarunner who set the course record at the Leadville 100 two years in a row dropped out of Western States this year, and the first issue he had was his hydration (he took in too many electrolytes). this shows that (1) even pros can get this wrong and (2) be sure to practice this in your training!
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