Quick Tip: How Much Do You Really Need to Eat on Race Day?

How much fuel should you take in on race day?

The conversation about what to eat on race day is an ongoing one in many parts of the running community.

Gels. Chews. Bars. Beans. Sports drinks. Real food.

The options are many, and there seem to be more products coming on the market all of the time.

But how much fuel do you actually need to eat on race day?

Perhaps that is the more important conversation to be had.

Can You Have Too Much to Eat on Race Day?


While many coaches and magazines and blogs preach the importance of making sure you eat enough during your race, too much fuel can ruin your race just as much as not eating enough.

In a conversation with one of my athletes after a recent half marathon, she said things were going well until about mile ten.

She said she started to feel nauseous at that point, and as you might imagine, it’s kind of hard to dig in for the last 3+ miles of a race when things aren’t sitting well in your stomach.

She wondered if maybe she didn’t take in enough fuel during the race, and that she was possibly running out of gas.

After hearing what fuel she did take in, I think the opposite is more likely true. I think she had too much to eat on race day.

How Many Calories Do You Actually Need?

Probably not as many as you think.

If you’re running a half marathon or less, odds are that you don’t need much for fuel.

Most exercise physiologists agree that our bodies are capable of storing enough glycogen in our muscles to power us through 90-120 minutes of exercise.

So if your race is going to be less than two hours, you’re pretty much good to go.

But what if your half marathon is going to be longer then two hours?

Well, then you might need a little something. But you really don’t need much.

A cup or two of Gatorade during the race will most likely suffice. And if you want to choke down a gel (though I don’t know why anyone would want to do that!), go for it.

But much more than that? It’s a bit overkill.

The longer that your race will be, the more you’re going to need to eat on race day.

So how much is too much?

There is a Limit to How Much Fuel You Can Actually Use

Again, using exercise science as a guide, humans are pretty much limited to only be able to break down/utilize ~200 calories of fuel per hour during exertion.

When you’re running a race, your body is working hard to keep your muscles firing and your legs going mile after mile.

The process of digestion requires resources to be sent away from your legs and diverted to your stomach in order to break down whatever it is that you’re taking in for fuel to keep you going.

What happens if you take in more than you can break down during exercise?

At first, not too much.

But if you keep flooding your stomach with more Tailwind, honey waffle stingers, or bananas your body eventually says enough is enough.

Too much food is coming in and we can’t keep up.

So your body does what it needs to reduce the amount of fuel in your stomach…

Yeah, it’s not pretty when you take in more than your body can handle during a race.

In the situation with my runner, I estimate she took in between 550 and 600 calories during her half marathon that she finished in a hair over two hours.

And if she started feeling nauseous around mile ten, I think you can probably assume that she took in almost all of those calories before that point.

So ~550 calories in an hour in a half?

Might be a bit too much…

Do You Need to Sart Counting Calories Now?

The last thing you need to do is start counting calories during your race to make sure you’re not taking in too much fuel during your race.

Instead, be aware of how many calories you actually need to take in during the race and how many calories are in the fuel sources that you’re going to use.

Do that, and you’ll be good to go.

A Benefit of Becoming Fat-Adapted?

You are probably aware that I’ve dedicated 2018 to experiment with the impact of HR training.

What you may not be aware of is that my original experiment was to be with eating fewer carbs and more fats in my regular diet.

But it turns out that in order to become a fat-adapted athlete, you also need to embrace the principles of running easy.

Anyway, I’ve noticed a funny thing lately when it comes to what I need to eat on race day.

Basically, I don’t think I need to eat much at all.

At Pocatello, I took in a fair number of calories.

I had two water bottles, each with a packet of Tailwind in them, at the start of the race.

I had a couple of Tailwind packets on the ready for whenever I needed to refill my bottles and I had a Picky Bar with me as well.

All told, I probably took in between 500 and 600 calories during that race (4:27 was my finish time).

While I was reflecting on the race, I wondered if I really needed that many calories during the race.

So when Prairie Fire rolled around 5 weeks later, I set out to test myself and how many calories I needed to eat on race day.

Instead of putting Tailwind in my bottles at the start, I simply filled them with water and some Vitamin C powder.

At about mile 18, I consolidated my water into one bottle and refilled the other with water + Tailwind.

I finished this race with 4:21 on the clock, and probably didn’t take in more than 100 calories on the day.

Then, a week later, I did basically the same thing at the 7 Bridges Marathon.

The only difference was that I had a small piece of banana and a handful of potato chips at about the same time that I added the Tailwind to my bottle.

So all in all, maybe 150 calories in Chattanooga while running a new PR (4:04).

In all three of those races, I was able to negative split on the day and felt strong all the way to the finish line.

Yes, my legs were tired. But there was never any feelings of fading and I wasn’t worried about a bonking at all.

Proponents of fat adaptation make the claim that once you become fully fat adapted, you don’t really need to take in many calories during a race and you become virtually bonk-proof.

I’m not sure I’d go that far just yet, but I do believe that the less you need to eat on race day, the better.

Is it possible to take in too much fuel during a race? #runchat Click To Tweet

What Do You Eat on Race Day?

Want to Support the Continued Growth & Production of the Show?

Check out the support page for ideas and suggestions of ways you can help me grow the show. And remember, not all support involves money. Some of the best ways you can show your support are 100% free.

Subscribe to the Show

Never miss another episode of the Diz Runs With podcast by subscribing to the show, and for my fellow Apple fans out there, it’s never been easier now that the podcast app is native on the new operating system. iPhone/iPod/iPad users click here. Android users click here. SoundCloud users click here.

Please Give Me Some Feedback!

Take the 6 question listener survey to help me shape the future of this podcast.

Register for a Free Race Training Plan

Every month, I’m giving away a FREE training plan for the race of your choice. For details/information, and to sign up, just click here.

Join The Tribe!

There’s always room for more members of the tribe! Both the Facebook group and the email group provide opportunities that can’t be found anywhere else. The Facebook group is still small, but it is a great way to connect with fellow runners and foster community amongst like-minded individuals. The email group is THE way to stay up to date about future guests on the show, as well as getting some other freebies and offers that aren’t available to anyone else. If you’ve got questions about either/both, just let me know!


Some of the links in this post may be affiliate links. This simply means that if you decide to make a purchase using one of the links, I get paid a small commission at no extra expense to you.

2 replies
  1. Matthew Ricardo
    Matthew Ricardo says:

    Really enjoyed this episode and certainly something that has been on my mind, being fat adapted I have been wondering if I really need any fuel at all. I was so glad to hear that you don’t really need to fuel and that there is a chance to over fuel. Thanks

    • Denny
      Denny says:

      Glad you enjoyed it Matthew! No matter what anyone else says, there is no “one right way” to do anything. If you’re fat adapted and don’t need fuel, then don’t fuel! One less thing to worry about on race day.


Leave a Reply

Want to join the discussion?
Feel free to contribute!

Leave a Reply

Your email address will not be published. Required fields are marked *