Fueling for the Marathon


Ask 100 marathoners how they fuel and you’ll get 100 different answers. It seems that marathon fueling is so individual that it simply takes lots of trial and error in training and tune-up races to find the strategy that works best for you.

After working with thousands of marathoners from charity marathon groups to Boston Qualifiers to Olympians, I wanted to provide a quick overview of the three most common strategies that I’ve seen work. These are good starting points as you begin your experiment to find the best fueling strategy for your next marathon.

Three Common Marathon Fueling Strategies

Strategy #1) Fast Acting Carbohydrates – The Traditional Strategy

Early in exercise science, researchers found that blood glucose dropped across the marathon and a drop in blood glucose results in decreased performance. This makes sense, of course, because even if you aren’t running a marathon, your blood glucose level will fall after 2-4 hours. Since the marathon lasts 2, 3, 4, 5 and even 6+ hours, it makes sense you’d need to fuel to maintain your blood glucose level.

While the blood glucose level is really important to fuel your brain, running also pulls some glucose from the blood so as you run your marathon, you need glucose in the blood to supplement the intramuscular fat and carbohydrates that are the primary fuels for marathon running.

So, runners learned that we need to fuel during the marathon and this research coincided with the boom in the sports drinks industry. Drink formulations centered around fast absorbing carbohydrates that emptied from the stomach quickly, got absorbed from the intestines quickly and thus boosted blood glucose levels quickly (and provided some electrolytes as well). This would then keep the brain happy (it uses glucose and tightly monitors blood glucose levels) and would provide some glucose for the working muscles.

This led to the traditional fueling strategy that most runners have used (or at least started with). You dose frequently with fast-acting carbohydrates to boost blood glucose levels. Runners use any combination of sports drinks and/or gels as part of this strategy and runners are now even using candy and other fast-acting carbohydrates to get this quick shot of glucose into the blood stream.

Marathoners have been encouraged to drink 4-8 ounces of sports drink every 15 minutes and/or to take a gel every 30-45 minutes to keep glucose moving through the GI system and into the blood stream. Rough guidelines are 30-90 grams of carbohydrates per hour in this strategy. (You will also hear 150-350 calories per hour in addition to 24-32 ounces of fluid containing electrolytes.)

The main reason for the frequent dosing is that as the carbohydrates are quickly absorbed and raise the glucose in the blood very quickly, the brain senses this (and remember I said it tightly monitors the blood glucose level) and triggers the release of insulin to lower the blood glucose level to keep it from going too high. So, the next dose was designed to catch the blood glucose before it fell too low (you often hear this as a sugar crash). This rise and fall (or commonly called the spike and crash) cycle would be interrupted by the regular dump of glucose into the blood stream so that the blood glucose level would remain at optimal levels.

This has been a popular strategy and there are hundreds of products available that aim to provide fast-acting carbohydrates in lots of different flavors, textures and carbohydrate types (glucose, sucrose, fructose, maltodextrin, etc.). And, these products are often the type provided by races on the course (and race websites will let you know the drinks/gels that will be on the course). As a result, most runners begin their search for their optimal marathon fueling with this traditional fueling method.

Strategy #2) Slow Acting Carbohydrates – The Alternative Strategy

While Strategy #1 has been popular, it can be problematic and has led to the development of this new slow-acting carbohydrate strategy.

Here’s the back-story: As you run the marathon, your gut gets dehydrated and blood is shunted away from it to the working muscles. This is a positive for your muscles but is a big negative for your GI tract. It can no longer tolerate as concentrated or as much carbohydrate as it could earlier in the race. You hear this when runners mention that the gel or drink that tasted so good at mile 5 made them want to vomit at mile 20.

This change in the GI tract makes Strategy #1 a big challenge for many runners. Not only do you have the challenge of making sure you dose at the right intervals to avoid the “sugar crash” but just when you need carbohydrates for the last part of the race, your body can’t tolerate it as well (which is why it’s recommended that you dilute your carbohydrates more in the latter parts of the race). Unfortunately, most runners simply stop ingesting as much fuel since their GI system is upset and this leads to under fueling and often a slow down. Stand at the 25-mile mark of any marathon and you’ll see lots of runners (and I’ve been one) who clearly stopped fueling adequately and are left to struggle to the finish line.

That’s where strategy #2 comes in. In this strategy, you aren’t using fast-acting carbohydrates that create the quick shuttling of carbohydrates from the gut to the blood stream (and creates the spike/crash cycle). Instead, you use slow-absorbing carbohydrates that maintain a steady blood glucose level and are kinder on a dehydrated GI tract.

Ultra runners have done this for years and a visit to any ultra aid stations will look more like a buffet at potluck party than the usual tables of water and sports drink (and the occasional gel station) at most marathons. I, myself, made the switch to this strategy a few years ago and found it to easily overcome the issues I had with the spike/crash and GI upset in marathons (from using Strategy #1).

There is a growing collection of products where the carbohydrate source is more slowly absorbed and therefore the blood glucose remains stable. And, runners are using more food and food-like products (dates and figs seem to be very popular at the moment). Though it should be noted that you still must work out the amount to ingest so your blood glucose level doesn’t drop.

For example, I use UCAN (full disclosure they now sponsor me) in my marathons. This carbohydrate is manipulated by heat and water so it is absorbed more slowly to avoid the spike and crash. You “feed” with it every hour of the race (one scoop/packet each hour) to provide glucose to the brain and working muscles but your blood glucose level stays at a more steady level instead of the rapid increase and decrease like with the fast acting carbohydrates. Because you feed less frequently and because it’s easier on the GI tract, you avoid the GI upset that can occur late in the race. That’s been a win-win for me and many other runners. Another big plus is that the regimen on race day is much simpler. You just get your carbohydrates once every hour and then just need to drink water and electrolytes in between. Super simple.

As I’ve advocated before, carrying your own fuel allows you to control what and when you feed so you aren’t reliant on the race to provide the same concoction you’ve been training with. (There’s been more than one race where the sports drink on course wasn’t mixed correctly leading to many upset stomachs.)

UCAN comes in powder and portable forms, so it can be mixed as a liquid or carried like a gel. No matter your marathon time, you can simply feed once every hour to maintain steady energy. The same goes with food (fruits and nuts seem to be popular) and food-like products (baby food, apple sauce are common ones). You just work out in your training the frequency of ingestion so you maintain energy. Then, you just drink water and electrolytes (super easy on the stomach) every 15 minutes to stay hydrated.

As I mentioned, I’ve had better success with this strategy than the traditional strategy but there are a few considerations. First, you don’t get the “high” from the sugar rush at every feeding. Runners often find they have energy but if they are used to this rush of energy, they may find the lack of it strange. Second, these products aren’t usually on the course so you must carry them with you. Now, I don’t see this as a problem given today’s hydration packs but if a runner isn’t prepared to carry, then this strategy will not work. Third, just because it’s an easier method doesn’t mean you won’t need to experiment. It will still take several long runs, hard workouts and tune-up races to fully dial in your optimal feeding schedule.

That said, I find this strategy to virtually cure issues with the spike/crash and GI upset in the marathon and highly recommend you give it a try.

Strategy #3) The Combo Strategy

This last strategy is becoming very popular and I suspect will be the go-to strategy for most runners in the future (unless some breakthrough product/strategy is discovered). In the Combo Strategy, you use the slow-acting method (Strategy #2) for the bulk of the race but then add fast-acting carbohydrates (Strategy #1) in the last 30-45 minutes of the race. This seems to provide the best of both worlds. You have steady energy for the bulk of the race and avoid the GI issues found with the fast-acting carbohydrates but then get the big energy burst in the home stretch.

For example, a runner might use UCAN or another slow-acting carbohydrate for the bulk of the race but then supplement with a fast-acting gel or sports drink in the last 30-45 minutes for the “sugar high.” Some runners even choose a caffeinated fast-acting carbohydrate source for an even bigger mental boost.

Using this combo method, you avoid the issues early in the race so your GI tract is more receptive to the (diluted) fast acting carbohydrates late in the race. And recent neuroscience research shows that if the brain senses carbohydrates when you are feeling tired, it quickly experiences less fatigue so you can power through to the finish line. After all, you just need to avoid low energy (physically and mentally) in the last 10K of the marathon to hold your pace and achieve your goal.

Final Thoughts

As with most things in running, it’s hard to find a one-size-fits-all with marathon fueling. My hope with this section is to provide some insights into the common fueling methods so you can experiment to see what works for you. And this should be the biggest take away. It all comes down to what works for you. And the only way to determine that is with experimentation.

Try these methods in a few long runs. See what you find works. Then once you have it dialed in on a long run, try it in a goal pace workout and see if it works in a more intense situation. Then once that is dialed in, try it in a tune up race. Then finally after learning from these experiences and tweaking your plan, you can feel very confident that you have the best strategy for you.


Fueling How-to

Strategy 1 – Fast Acting Carbohydrates

Ingest 4-8 ounces of sports drink every 15 minutes and/or an energy gel every 30-45 minutes. Most sports drinks and gels also include electrolytes.

Dilute the carbohydrates with more water later in the race to account of the compromised GI tract.

Strategy 2 – Slow Acting Carbohydrates

For UCAN, drink a serving of Energy Powder 30-60 minutes before the start and then 1 serving Edge Energy every hour.

For food/food-like products, ingest every 30-60 minutes depending on the product. Experiment to see the quantity and frequency that provides the best energy with the least GI distress.

For both UCAN and food, drink water with electrolytes (but no fast acting carbohydrates) every 15 minutes.

Strategy 3 – The Combo Strategy

For all but the last 30-45 minutes, use the Strategy 2 regimen above.

In the last 30-45 minutes, ingest a gel (once) or ingest sports drink (4-8 ounces every 15 minutes). Add caffeine if you like.

Written By Greg McMillan
Called “one of the best and smartest distance running coaches in America” by Runner’s World’s Amby Burfoot, Greg McMillan is renowned for his ability to combine the science of endurance performance with the art of real-world coaching. While getting his graduate degree in Exercise Science he created the ever-popular McMillan Running Calculator – called “The Best Running Calculator” by Outside Magazine. A National Champion runner himself, Greg coaches runners from beginners to Boston Qualifiers (15,000+ and counting!) to Olympians.

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