Most of us have been given the advice to fuel up before long runs. There’s good reason for that, too: if you are going long, having a couple hundred calories beforehand can help fuel your efforts and keep your energy levels steady. Taking in calories while out there can also help top off your glycogen stores and allow you to finish strong. Plus, if you are training for a half or full marathon, it’s a good idea to practice your fueling before the big day.
In spite of that, however, there’s also value in training your body to run on no fuel at all. It might sound scary if you’ve never tried it before, but you can slowly condition your body to go long without fuel. The ultimate goal with this approach? Teaching your body to tap into its own fat stores for fuel.
Let me be upfront here: this isn’t for the purpose of losing weight, although that may be a side benefit of this type of training. Rather, it’s a way to help you avoid the dreaded bonk at the end of a long race.
Even the leanest of runners—someone with a body fat of only six percent– has enough fat stores to fuel a running effort of several hours. That is, if his or her body can tap into it. Compare this to depending on sugar, or glycogen, which will run out before very long, even if you are replacing some of it with gels and sports drinks.
So how do you go about teaching your body to draw from fat stores? By running in a glycogen depleted state. That means starting a run without ingesting any calories and completing the run without anything more than water.
Clearly, for someone used to consuming calories before runs, this can be a shock to the system. For this reason, you have to work your way into it.
Start at the beginning of a training cycle, when your long runs are in the 10- to 12-mile range. Make sure that your pace is nice and easy. Then set out and give it a go. Odds are you might feel pretty spent by the end of this effort. The first two such runs I did in a glycogen depleted state were awful, believe me. But by the third one, I was getting used to things.
Gradually increase the amount of time you run in this “hungry” state each week until you get up to as long as an 18- or 20-miler. Once you are hitting these bigger numbers, it’s a good idea to alternate long runs in a fueled and unfueled state. This will allow your body to relearn how to comfortably use carbohydrate supplements, which will be necessary come race day. You may find, however, that you don’t need as much of these types of fuel as you used to before starting on the training.
Make sure that you always have calories readily available when you finish any glycogen depleted run. You’ll need to replenish your body and help it begin the repair process right away. And believe me, nothing will taste so good as that first sip of sports drink or chocolate milk after you’ve run on nothing at all. Good luck!