Fueling Your Endurance
Whether you are training for your first marathon or preparing for your 3rd triathlon, figuring out how to fuel your endurance event can be difficult to maneuver. There are TONS of products and advice to sift through. Here is a quick guide to help ensure you are properly fueling during your next endurance event.
Why do we Fuel?
Understanding why we fuel during endurance events can be a helpful place to start in “finding your fuel” journey. To sum it up - we need energy to keep us moving! And this energy comes in the form of carbohydrates, which are our body’s main source of fuel. When we eat carbohydrates, they are broken down and stored as glycogen, primarily in muscles and in the liver (hence the need for optimal carbohydrate intake within our diets!). Glycogen is further broken down into a type of simple sugar called glucose, which is then readily taken in by our cells for fuel. We have limited glycogen storage capacities, though. The rate at which glycogen stores deplete depends on the duration and intensity of what you are doing. During moderate-to-intense aerobic activity, for example, these stores can diminish within a few hours. When this happens, muscles tire, fatigue takes over, and may find yourself “hitting the wall.” This is why eating something carbohydrate-rich during endurance exercise is important to maintain performance. (Fink, Mikesky, 2018).
Basic Recommendations
So, with that information in mind, here are a few basic recommendations for fueling during your event:
Fuel during activities > 70 min
Aim for 30-60g of carbohydrates every hour
If you choose to consume sports drinks, choose ones with a 6-8% carbohydrate-electrolyte content or around 14-20g carbohydrates/8 fl oz. Those of greater concentrations can slow carbohydrate absorption and cause diarrhea, bloating, and/or cramping due to their high osmolarities (Fink, Mikesky, 2018)
Side note. Gatorade actually has a high osmolarity- Go easy on it!
Hydrate ½ - 1 cup every 15-20 min
Note: Hot and humid race environments will increase sweat output and require more fluid intake
(Fink, Mikesky, 2018), (Kerksick et al., 2017)
What to Look for in Fuels
Fueling aids are usually designed with many of the above needs in mind. They can come in the form of gels, chews, bars, or drinks. Gels and chews are typically individually portioned and contain around 20-25g of carbohydrates. They may also be more easily tolerable compared to solid foods. To meet the above fueling needs, you would need to consume 1 around every 45 minutes.
Some things to look for in fueling products:
Mix of simple sugars (glucose, sucrose, maltodextrin, starches, fructose, galactose)- Consuming a blend of simple sugars can enhance the body’s utilization of carbohydrates during endurance exercise, particularly glucose, and fructose, and reduce the risk of stomach upset (Fink, Mikesky, 2018). You may be wondering what is so special about this dynamic duo- they are both carbohydrates. While that may be true, they take pathways within the body, which can be used to our advantage.
When we consume glucose during exercise, it first enters the small intestines and is quickly taken up by the muscles for use as energy. This is done with the help of an intestinal protein transporter called SGLT1. SGLT1 has a limit to how much glucose it can process, which is around 60g/hour. Excess glucose beyond this amount can’t be used and will cause excess amounts to remain in the small intestines (hypertonic environment). This hypertonic state attracts water into the small intestine in an attempt to dilute the high concentration of glucose. In turn, this can lead to gastrointestinal (GI) distress, and possibly the end of your long run.
In comes fructose.
In order for fructose to be used by the body for energy, it takes a pit stop in the liver to be processed into glucose. Compared with ingesting glucose alone, this “pit stop” is what delays fructose’s use as an immediate energy source. Fructose uses a protein transporter, independent of glucose, called GLUT5. This transporter also has a processing limit which is around 30g of fructose/hour.
Now, let’s pretend we are consuming a carbohydrate source that consists of 60g of glucose and 30g of fructose (2:1). When we exercise, the body will innately use the most readily available source of energy. Because fructose requires a detour to the liver to be processed into glucose which can then be used as energy, glucose is the first choice. But remember, we can only process up to 60g of glucose at a time. As glucose’s carrying capacity is reached, glucose will then be sourced by the processing of fructose, which can do so at 30g of fructose/hour.
Think of it as having two containers- container 1 can hold 60g worth of water, container 2 can hold 30g. Say we are given 90g of water and are instructed to fill each container to as much as they can hold, beginning with container 1. Well, when container 1 runs out of room, we will then have to use container 2.
How can we use this concept to our advantage? The differences in carrying capacities and processing methods between glucose and fructose allow athletes to maximize carbohydrate intake of 90g/hour using a 2:1 glucose-to-fructose ratio. Especially for ultra-endurance athletes, this advantage can be a game changer in maintaining peak performance.
(Fuchs et al., 2019) (Rowlands et al., 2015)
Electrolytes to replenish those lost in sweat- sodium, potassium, calcium, magnesium
Sometimes caffeine - a known performance booster. Make sure to read the label. Caffeine is not always tolerated by everyone.
Texture and flavor. This is a personal preference! Some people like the texture of chews, some like the gels, and some prefer bars - the choice is yours and depends on what your body can tolerate.
The Big Day
Whether you are participating in a half marathon, marathon, or Olympic triathlon, fueling for endurance events involves logistics and timing. Planning will be your friend. Research the availability of aid stations, what is offered at each, and how few and far between they are. Does the fuel they offer match what you have been training with? Or will you need to bring your own? Come prepared on race day with EXACTLY what you have been training with. Keeping up on your hydration needs will also be crucial. If you anticipate competing in hot and humid temperatures, you will naturally lose more electrolytes and fluids from sweating. Check the weather, check the humidity. Avoid surprises.
Long-distance Running
Your fuel clock should begin at the 0 second mark. If you are planning on fueling every ½ hour, you should do so within the first ½ hour of your run. Whatever method you choose to fuel with- gels, chews, bars, candy- you’ll need to plan a way to efficiently access them during your run. Hold them on your body somewhere. Fanny packs, water bottle jackets, arm bands, sports bras, pockets. Wherever you find most comfortable and easy to grab. Also make sure to take some sips of water with whatever you eat. Know the layout of the aid stations. If the race is providing the same fuel that you have been practicing with, this could save you carrying space. Just make sure to research the distance between each aid station to know when you will have the opportunity to fuel.
Holding a water bottle can be a great way to hydrate throughout. Some people use handheld water bottle jackets (sometimes these have little pockets for extra storage space), others prefer fuel belts. Some runners prefer not to hold anything and rely solely on the aid stations. Sipping on water versus taking in large volumes all at once can be easier to tolerate. Aid stations will usually offer either water or a sports beverage. Make sure you drink what you have trained with, and that you grab the right one! Practice the logistics of refilling your water bottle while you are running. This takes practice, but you can iron out the details before race day.
Triathlons
3 times the events, 3 times the fun!
Fueling for triathlons requires a bit more planning compared to single-event races. During the swim portion, fueling won’t be possible, so your first opportunity to eat something may not be until you are on your bike (bring in the pre-race meal plan!). Have your fuel ready to go when you hit your bike. Your fueling clock can start here. If you are choosing to eat solid foods, like bars, doing so on the bike may be easier for your body to tolerate them. Continue your fueling as you practiced. By the time you hit the running portion, your GI may only be able to tolerate easier-to-digest carbohydrate sources, like gels. This would be a good time to implement them. If you haven’t already been using gels on the bike, be sure you consider this if switching to gels during your run. It may be helpful to mix some in toward the end of your ride. Finish your run strong and continue fueling as you’ve practiced, including hydrating properly (see above).
Practice, Practice, Practice (your fueling)!
Especially if this is your first race. Training is not only essential to building endurance, but also for training your gut. Remember: Avoid race day surprises. Take in during your race what you know works for you and what you have trained with. Research what the event is offering to see if it matches what you have been fueling with. If not, come prepared. And remember: what works for your body may not work for someone else’s body. The process of trial and error truly shines as you find the right “fueling” fit for you.