Skip to content (Press Enter)

GU's Magda Boulet: Fueling for an Ultramarathon Takes Personalization, Practice

Ultrarunner and VP of Product Development at GU Energy Labs Magda Boulet

Fueling for an ultramarathon is different than preparing your body for a 5K. At its simplest, the sheer distance of an ultra requires more calories to keep you going. But running 50K or 100 miles isn’t simple, so the best food to eat for an ultramarathon requires tinkering and personalization.

When it comes to racing and nutrition, Magdalena Boulet knows more than most. The pro runner was a 2008 Olympic marathoner and has run world-class times in distances from 5K to 100 miles, including her debut 100-miler, which was a win at the 2015 Western States Endurance Run.

When Boulet isn’t training and racing, she works as the VP of Product Development at GU Energy Labs and coaches post-collegiate runners at California’s Bay Area Track Club.

As the ultra scene continues to grow in popularity, new ultrarunners and curious bystanders alike wonder how to approach training and fueling for such a long race. And, with her professional expertise and personal experience, Boulet knows how to set herself up for success.

So, what do you eat when you may be running for more than a full day straight? It depends on your system, the race and the weather. Here’s how Boulet says you should fuel for an ultramarathon.

A runner opens a GU Energy Gel packet

What is the best way to approach nutrition if you are preparing for an ultra?

Have a plan. Invest time and effort in finding out what works for you. That’s my number one recommendation. There are lots of choices out there, and you can build your own plan. Everyone is different. What works for me might not work for you.

Eating as training is something we talk about at GU and it’s basically eating the right nutrients at the right time in the right amounts. Mostly the purpose is to support the demand that the workout requires of you that day and to optimize recovery and adaptation.

How do you fuel for a 100-mile race, specifically?

When fueling for a 100-mile race, people ask me about my approach. I ask about the course where you’re racing. My first 100-mile race was Western States. It was hot and dry, at altitude. I took the approach of basically fueling on Roctane nergy drink for 19 hours. It took me 19 hours to complete it. The plan was easy to execute. I took one bottle of Roctane per hour. Each bottle has 250 calories. I got all my electrolytes as well as amino acids.

I took a different approach for UTMB (Ultra-Trail du Mont-Blanc). That race took about 30 hours. Same 100-mile distance, but very different mountains. It was also cold, and I was running for most of the day and night. I took a very different approach. I ate a lot of stroopwafels at night. When I came through aid stations, I took broth and crackers because I was moving a lot slower.

There are so many nutrition choices out there (chews, gels, drinks, etc). How do you decide what type of fuel to consume?

If I’m running easy when it’s nice and cool and I’m just putting time on my feet, I do more solids like stroopwafels, chews or gels. It varies. It’s important to pay attention to how hot is it outside, too, since that has an effect on your ability to digest the fuel. Am I going to be sweating a lot more? Take that into consideration and build your own plan. Change within the training cycles. Be adaptable. Try different things.

For a hard session, like a race-pace effort that’s harder than easy conversational, there is less blood flow going to the stomach. Muscles require blood and during digestion, blood flow is limited. Lessening the demand on your gut is key. I shift toward liquids when it’s hot and humid.

Do you ever get tired of taking the same nutrition for such a long period of time?

For me, variety is important. I might get bored of the flavor I’m taking in during long sessions. I work for GU, and we have over 25 flavors of gels that we make. It’s important to pay attention to what flavors I’m taking on warm versus cold days. On hot days I go for citrus flavors like lemonade, and cold days or at night I go for chocolatey or more indulgent flavors. They are easier to digest when it's cold. The citrus flavors stimulate the drive to continue to drink and hydrate. They go well with running in a hot environment.

Runners drink from GU Energy water bottles during a workout

How much water should you drink after taking an energy gel?

It’s important to drink water any time we consume any type of calories when we run. For example, if you’re taking a gel that has 100 calories, you need to also take 100 ml (3.3 oz) of water to chase it down. That does not include the normal hydration needed per hour just to stay hydrated, which could be another 16 to 20 oz of water—sometimes more—when it’s hot. Fluids are necessary to stay hydrated. When you take a gel, chews or any form of calories, be sure to also get 100 ml water.

What are your tips to avoid GI distress in an ultra?

Practice your nutrition. Don’t do anything new on race day. Be aware of where your nutrition is coming from on race day. I rely on bringing my own nutrition with me versus getting too creative at aid stations and trying new stuff. Maybe you had too much or not enough sodium or the wrong calories. Stick to the plan. Research shows if you practice your plan and try to execute it, the chances of you having a successful race go up drastically. Leave nothing to chance. That’s my number one recommendation.

Again, every race is different like people are different. Tailoring your plan to the race is important. Keep in mind that like your muscles and heart are trainable, so is your gut. So preparing ahead of time and putting that nutrition plan into practice weeks before will make your nutrition plan on race day so much easier. On race day I make an effort never to think about nutrition. It’s on autopilot.

When GI distress does happen, backing off on effort is my next tip. The harder we work out, the less blood flow there is going to the digestion process. You’ll need to back off on your pace, lower the intensity and focus on hydration until your stomach calms down. Usually, people focus so much on calories in that they forget to chase it with the proper amount of water.

Finally, go for foods that are simple. I focus on the concept of “eat like a baby.” Don’t get too creative. If you end up drinking too much and get a sloshy stomach back off on the fluids and switch to solids. Keep the variety going and continue to problem-solve. Don’t rush through aid stations. Taking your time will help tremendously.


By Kate Schwartz. Schwartz has been running competitively for 20 years, and she currently runs with the Asheville Running Collective. She lives in Asheville, NC, with her husband, Alex, and their cat, Clementine.

Keep Reading