Should You Always Fuel During your Marathon Long Run?
Fueling before, during and after your marathon long run is critical to achieving your goals. Should you always carb load or is it better not to on occasion? Should you take only water and energy gels, or just sports drink? Perhaps it’s an elaborate combination of all of that. Of course, you need to decide which brand and flavor agrees with your system, and practice what to eat the night before your long run.
While all that is important, below is perhaps a new way to think about the whole concept of fueling to maximize your marathon long run.
My Personal Experiment
This past year I’ve been experimenting with different ways to fuel my marathon long runs. Initially, I stopped fueling (except for water/nuun) on any runs 90 minutes or less. At first it was tough, but over time, I’ve found I can now I can go for a run of 2 – 2.5 hours without the need for additional fuel.
I’ve been learning how my body makes adaptations regarding fuel use. By not ingesting additional carbohydrates (in the form of gels, chews, sports drink etc.) during a long run, I’m training it to be able to use fat as a fuel source at a faster pace.
This is slightly more complicated than simply denying yourself fuel during a marathon long run. Below is a very brief overview of how this works, and a few suggestions you may consider during your next long run.
How Your Body Adapts to Training
One of the key elements to marathon training is teaching your body to burn fat as a fuel source rather than simply carbohydrates. I’ve been reading The Science of Running by Steve Magness, and there is a great chapter on the Genetics of Training where he explains how training stimulus brings about functional change.
This is highly simplified (get the book if you want to geek out). Basically, your body goes through five stages of adaptation to reach your desired training effect.
- You apply a Training Stimulus (long run, speed work, etc). This needs to be something more difficult than what you’ve done before. The body must be “put in a state of crisis to trigger the stages of adaptation.“
- Messengers tell the body that something is wrong and it needs to be fixed and made stronger for next time. This is the “alarm” stage.
- Signal Pathways respond to the alarm and take steps to make sure that an adaptation can happen. It’s like gathering data to tell your body what to do different next time so the problem doesn’t happen again.
- A Genetic response occurs to “build” a solution using the data from the signal pathways. It “builds the final product” by increasing gene expression.
- Functional adaptation occurs over the series of several weeks and months of training. The process gets repeated again and again. It’s why running 3 miles feels easy after weeks of medium and long runs.
How your Body Adapts to Burning Fat
Burning fat as a fuel source as long as possible is key to marathon success. If you rely on only burning carbs (the readily available source of fuel), you’ll eventually bonk no matter how much you ingest during the race.
A training stimulus that helps this process of adaptation to burning fat is not fueling during some of your marathon long runs. For example;
During a two hour run where you haven’t taken any additional fuel, the messengers tell your body, “hey, we don’t have any more carbs to burn, what else can we use?” The signal pathways scour the body to find other available fuel sources and make a plan to start burring more of those (fat) as fuel during your next run. When you continue to do this over and over, eventually you’re able to go much long and farther without relying on additional fuel.
According to Greg McMilllian,
We want to deny the body carbohydrates in these runs so that the muscles will become better at sparing the carbohydrate stores, more efficient at burning fat and used to running with lowered blood glucose levels.
When to Fuel and when not to Fuel During Training
When you’re doing a marathon long run longer than three hours, you should definitely take in something. For a 10 minute per mile runner, that’s about 18 miles. Every runner is different, but a good rule of thumb is approximately every 45 – 60 minutes.
There are two states you can run in: glycogen depleted and glycogen loaded. Glycogen is just stored carbohydrates, so we’ll call it carb full and carb empty.
Running in a carb full state might look like you getting up and having a small meal (toast with peanut butter and a banana perhaps), wait 60 – 90 minutes, then go for a long run or hard workout and consume energy gels or sports drink during your run.
Running carb empty means you go for your run in the morning without the small meal, and without ingesting anything other than water (or an electrolyte drink like nuun). Always take water!
By strategically running in this carb empty state, you’re focusing on the fuel adaptations mentioned above.
Jeff Gaudette notes that,
…the research makes a strong case that occasional long runs in a fasted state will improve glycogen storage and fat utilization, but extended training or multiple long runs in the fasted state will impair performance and does not provide further benefits to fat utilization.
He also makes a case for carb full runs, primarily stating that it will help you complete the desired workout to your best ability, and it can aid in recovery.
Try this on Your next Marathon Long Run
Ideally you would do this early in your training, or before you start to get in to the 18+ mile long run. That being said, everyone responds differently to the rigors of training, so you may need to experiment a bit.
Assuming you are more than four weeks away from your race, do your next long run in a carb empty state. As noted above, it will boost your body’s ability to burn fat, which will help prevent the marathon bonk and allow you to run your pace longer.
Regardless of what you do, make sure you’re practicing your fueling strategy now, and you are racing with fully stocked glycogen stores! To get a personalized plan, checkout the Marathon Nutrition Blueprint (affiliate link) from Runners Connect.
How do you fuel during your long runs?