The words “fasting” and “training” may seem like polar opposites. After all, food = energy and we need energy to train effectively. While this is definitely true, fasted training does have its benefits. Let’s first tap into the key source of our energy as runners, glycogen, and explain how it works.
Glycogen is a type of carbohydrate stored in our body. It is a primary energy source our body uses when it is doing anything at a moderately hard intensity. Why glycogen? Because it can be converted to energy very quickly and efficiently.
Glycogen enables us to run fast during long races. Here’s the catch though – we do not have an unlimited supply of glycogen no matter how much pasta we eat! When this happens, our body switches to the other energy source, namely fat. Fat CANNOT be used as efficiently as glycogen so the body is forced to slow down (see “WALL, MARATHON”).
Because no one wants to slow down, we want our bodies to adapt in two ways throughout our training.
- We want to teach our bodies to store more glycogen than ever before. The bigger our tank, the more we can hold.
- We want to teach our bodies to utilize more fat than before while running at our race pace.
Both of these adaptations are improved with fasted training. Why? When our bodies are low in glycogen, it triggers a release of amino acids which subsequently increases fat oxidization and metabolism. In other words, it forces our bodies to use fat as a fuel source!
The more we use fat as a fuel source in training, the more efficient our body becomes at using it. Thus, we are able to run faster paces (like your race pace!). The less glycogen we use at that pace, the longer it will last, ideally the full race distance.
Let’s look at some practical tips for training in a fasted state.
Rule #1 – Get rid of the carbs.
The easiest way to train in a fasted state is to do your runs in the morning before you eat breakfast. If you’re an afternoon runner, maybe going light on the lunch or eating a low-carb lunch will do the trick. Furthermore, ingesting gels or sports drinks with sugar on your run will detract from any benefit since those are designed to replenish glycogen stores.
Rule #2 – Long runs only.
You also don’t need to worry about it if you are not going on a substantially long run. Since our bodies don’t use much glycogen while we are at rest, it will still take a run of at least 90 minutes to deplete your existing glycogen stores. Going for a short 4-mile run upon waking isn’t going to tap into the adaptation that we are looking for.
Rule #3 – Slow down.
We will teach our body to use more fat if we are running at an easy pace. Remember, fat is not easily converted to energy, so if we are always running too fast to use it, our bodies will never learn to use it at all! Don’t try and be a hero when doing depleted, or fasted, runs.
Rule #4 – Don’t fast if you don’t need to.
Research shows that those who fast have improved fat metabolism – the ability to burn fat as energy. Research also shows that this adaptation has no effect on running 5k’s and 10k’s! We have more than enough glycogen stored in our body to run those races without running low.
The average person has enough glycogen to last two hours. If you are racing a distance for less than that time, skip the depleted runs. For longer races, however, glycogen storage and fat utilization is a key adaptation we want.
Rule #5 – Use in moderation.
If you DO decide that fasted training is for you, don’t go crazy with it! As I said earlier, there will be no added benefit for shorter runs. But furthermore, extended bouts of training in a depleted state have been shown to impair performance.
You simply can’t handle as much of a workload if you are always fasting. And we know that a higher capacity for training breeds the best results. I like to stick to no more than 2 depleted runs per month.
Rule #6 – Use early in training cycle.
Save your last 3-4 quality long runs to practice nutrition and fueling strategy. Eat well the night before, take any gels, and get your plan down for race day. That is not the time to deprive the body of nutrients.
Also, generally your long runs are shorter earlier in the training cycle. I recommend 14 miles for the longest fasted run. Anything longer and you risk completely bonking and ruining the workout. I remember last summer attempting a 19 mile long run after fasting. I was too aggressive with it and had to stop at mile 17. Instead of hitting the next workout hard, I was stuck still trying to recover!
Rule #7 – Fill up the tank afterwards.
This is how we teach our bodies to store more glycogen (the 1st desired adaptation from above). Eat a good glycogen (ie: carbohydrate) rich meal in the 30 minutes following the workout. Because your body is low on the stuff, it is craving it and wants to stock up on it!
THE ART OF FASTED TRAINING
Fasted training walks a fine line between running our bodies into the ground and achieving the desired adaptation. It definitely takes practice in knowing your limits and being able to listen to your body. Hopefully these rules will help you carry it out effectively in your training and avoid that slow-down in your next race!
