Reflections on a Week of Running On an Empty Stomach

A big breakfast on a table. You don't need to eat before running, unless you want to.

One of the most frequently asked questions about running is – Can I run on an empty stomach? Or should I eat something before I run?

To which I always answer, “Yes,” and “No, unless you want to.”

There’s plenty of valid, scientific reasons for this. Your body has plenty of fuel in the form of stored fat, and even after an overnight fast you likely won’t have exhausted the glycogen stored in your muscles.

You can more about that in this post – Running on an Empty Stomach: Is It a Good or Bad Idea?

But today I wanted to put my money where my mouth is and discuss my own running. I almost never eat before running, and over the past week I’ve been out running five times on an empty stomach. This has run the gamut from an easy 45 minute run to a hard interval session to a relatively long run.

In each case, I was fine. But let me reflect on each run in a bit more detail.

The Easy Runs – Tuesday and Thursday

Tuesday and Thursday are typically my easy days.

Tuesday is sometimes a trail run. Other times, I incorporate some strides or hills for an easy workout. But the bulk of the run is easy mileage. Thursday is always a recovery day, since Wednesday is a true workout.

These are the clearest examples of when it truly doesn’t matter if you’ve “fueled” or not.

Running at an easy pace, your body is going to utilize a higher proportion of fat for fuel than carbs. Given the shorter nature of the runs, you’re unlikely to come anywhere close to exhausting your stored muscle glycogen, even if you haven’t been careful to top them off.

This morning, I woke up, had a cup of coffee, and went out for my run. I ran 4.5 miles at an easy pace. My pace was about 9:30/mi, consistent with the improved easy pace that I’ve seen over the past couple weeks, and my heart rate was a comfortable 141. I didn’t feel hungry, and at no point did I feel weak or out of energy.

Tuesday, I woke up and had my coffee, but I didn’t immediately go out for a run. I had someone coming to work on the bathroom, so I needed to be available in the morning. Instead, I got to work early so that I’d have some free time in the afternoon. I usually eat breakfast after I run, and it’s not uncommon for me to fast until lunch time if I haven’t gone for a run.

By the time I got ready to go out for my run – around 1pm – I still hadn’t eaten anything. So I’d fasted from the night before (pizza for dinner around 8pm, along with a couple beers) until well after noon. I was a little hopped up on caffeine, having drank perhaps one too many cups of coffee, so I was slightly jittery. But I felt fine as I went out for my run.

I don’t have accurate heart rate data, because my watch goofed a bit and locked on to my cadence for the second half of the run. I’d say it was slightly more elevated – closer to 145 to 148 – and I was a little tired, but I would chalk that up to having put in a lot of hard running over the previous week. Regardless, I put in 4.75 miles at a pace of around 9:45/mi. Again, I didn’t feel hungry or weak, although I was definitely ready for a big bowl of cereal when I got back home.

On these easy runs, I feel fine running on an empty stomach.

Wednesday and Saturday – Hard Intervals

Wednesday and Saturday are typically my workout days.

This is the type of run that you might worry about actually needing some fuel for. Running at a sustained, intense pace typically pushes the body to burn a higher proportion of glycogen to fat as fuel. But still, the total volume of these workouts is not near enough to exhaust my stored muscle glycogen.

This week, I ran a longer interval session (5x800m at around 3k to 5k pace) on Wednesday and a shorter interval session (5x90s at around 800m to 1600m pace).

I woke up yesterday and went about my morning routine a little early. I had my morning coffee, geared up, and hit the cold road. After my warm-up, I did my workout. My times were significantly improved over the previous weeks workout, and I averaged around 6:50-7:00/mi pace for the intervals.

The total volume of hard running was 2.5 miles and the overall run (including warm up, cool down, and recovery) was a little over 6 miles. Again, I felt fine throughout the workout and I never felt weak or hungry. In fact, I felt stronger than I had the week before.

My routine Saturday was similar, although I woke up a little later. Without any other pressing matters for the day, I hit the road a little later (around 9:30).

The intervals were shorter and more intense – 5x90s at about 6:00-6:15/mi pace. The total volume of hard running was much lower than Wednesday’s workout, a little under 1.25 miles. With the warm up, cool down, and recoveries included, I ran about 6 miles in total.

At no point in these workouts did I feel like I was low on fuel or energy. I eat a healthy amount, including a good amount of carbs, so I assume that I usually have enough energy stored up to handle these workouts without any additional fuel in the morning.

In the spring, I’ll be training for a half marathon. At that point, I’m sure the volume of hard running and the length of my workouts will increase. At that point, I might reconsider. But given the fact that these workouts are under an hour and I’m only putting in a couple miles of hard running, I see no need (and feel no need) to worry about nutrition.

Sunday – The Long Run

Finally, Sunday is my long run.

It’s not all that long at the moment, since I’m focusing on my 5k time for the next few weeks.

This Sunday, I woke up, had my coffee, and hit the road for 10 miles. I ran the first 5 miles easy and on the last 5 I increased the pace a little bit to about marathon pace. My overall pace was 9:25/mi, and the earlier ones were closer to 10:00/mile with the latter ones closer to 9:00/mi. My average heart rate was 148, and again it was lower in the first half and a bit higher in the second half.

I finished the ten miles strong and I could easily have kept going. Overall elapsed time was a little over an hour and a half. I got home and walked the dog before I stopped to eat breakfast.

The long run is where you’re most likely to run out of muscle glycogen. But, at this point, I’m not running far enough for that to even be a concern. I was on my feet less than two hours, and a general rule of thumb is that you can run for two to two and a half hours before running out of glycogen.

I’d also wager that, given the easy nature of the run, that stored energy will last even longer. For the first half of the run, my body was likely burning more fat than carb for fuel.

Even if my glycogen stores did run low – and when I increase my volume during half marathon training in the spring, they will – that’s fine with me. One of the purposes of the long run, in my view, is to stress my body’s ability to store and utilize fuel. It’s only by running the gas tank low that I can challenge my body to adapt and use fuel more efficiently.

Ultimately, that will help me run a better half marathon and a better marathon when I train for the full race in the fall.

A light breakfast of yogurt, fruit, and granola. In case you don't want to run on an empty stomach.
There are some situations where you might want to eat before you run. But generally, it’s not necessary for training runs.

So Should I Bother Eating Before Training Runs?

Right now, I run 5 times a week for a total of about 30 miles. You just saw an example of what my typical week looks like, with two easy runs, two workouts, and a long run.

I ran the entire week on an empty stomach, and I never once had a second thought. I wasn’t weak, lightheaded, or dizzy. At no point did I feel like I was running out of energy.

If the lack of fuel had any impact on my performance, I wouldn’t know. My performance in both intervals was better than the week before, and I’m continuing to progress towards my goal time in a 5k time trial in January.

When I shift into higher gear for half marathon and marathon training next year, this might change. But I doubt it.

At this point, the only runs that I plan on eating before are some of my truly long runs in the marathon plan. And that will be less about fueling for the long run than making sure my body can handle running after eating.

The only other reason I might consider eating before my runs is if I need to do so to maintain my weight. I’ve reached equilibrium right now at around 165 to 170 pounds with my current volume.

But if that volume increases, it might cause my weight to drop. To make sure I eat enough during the day, I might end up eating a snack before my run just to pack in a few extra calories. But we’ll see how that goes next year.

Reflections on a Week of Running On an Empty Stomach

Leave a Reply

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Scroll to top