How to DNF Your Next Ultra

Disregarding smart nutrition strategies is a surefire way to not reach the finish line. Here are the most effective ways to sabotage your next big race.

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Whether it’s your first ultra or 50th, dialing in your nutrition for your next big event can help make or break the experience. Do things the right way and you can end up crossing that finish line with energy to spare and no excessive time spent in the portaloos. 

But what about the beloved DNF? It’s something nobody wants to talk about, but may very well be a rite of passage for ultrarunners. 

To do things the right way, you need to understand the potential outcomes of doing things the wrong way. But what does “the right way” look like? Here’s everything you need to know to successfully DNF your next ultra.

RELATED: The Do’s and Don’ts of Fueling for Trail Races

Consume 100 calories per hour for 100 miles. (Don’t you just love consuming your own muscles for fuel?)

While you may have heard that it’s best to fuel with 30-40 percent of the energy you burn every hour, if you really want to DNF, you’ll aim for much less. Once your body runs out of those pesky carbohydrates that help with energy production, it’ll start solely relying on fat stores and your own muscles for fuel during your training and racing. You might not notice it at first, but eventually your key bonking moment will surface and you will slow to a walk. You might be able to keep going for a while, but then you start peeing blood and your heart rate becomes irregular. That signals that it’s game over (unless you only want to have a semi-functioning pair of kidneys and cardiovascular system, of course).

The reality: Ideally, creating an endurance fueling plan that covers all of your bases (calories, carbohydrates, and sodium) and is based on your body frame size, the goal race, and the terrain is what you want to come up with ahead of time (maybe have a fueling article link).  The International Society of Sports Nutrition recommends 200-400 calories per hour as a starting point for ultrarunning intake if you want to get the most out of your training and racing without negative side effects. 

RELATED: More Carbs Correlates With Less GI Distress in Runners

No need for pre-run fuel. (Getting injured frequently is living the dream!)

Fasted training definitely makes you a tougher athlete, just don’t mind the fact that it can lead to increased risk for muscle protein breakdown and bone breakdown. (Hello tendon and ligament injuries, as well as stress fractures!) It can also save you some precious kcals and make you a fat-burning machine. (I mean, it’s as if training doesn’t do that anyway!)

The reality: Fasted training really should not be a part of your regular training routine unless you want to increase your injury risk and performance. According to this 2020 review, while fasted training can increase fat oxidation, it does result in decreased physical performance. 

To get a little more nuanced, there are certain situations where you could engage in training sessions without fuel including: 

1) If you are doing a training session less than 60 minutes in duration

2) You are doing an easy effort training session 

When you should NOT do fasted training:

1) If you are hungry

2) If you are at risk for Relative Energy Deficiency in Sport, have an eating disorder or 

eating disorder history 

3) If you are exercising longer than 60 minutes in duration

4) If you are doing higher-intensity training 

5) You want to train your gut to handle fuel 

RELATED: How To Not Screw Up Your Pre-Race Breakfast

Skipping meals definitely helps you #stayhard. (Don’t you just hate eating food?)

Who really needs to meet their energy demands for their training? Being in a constant low-energy-available state can up your toughness factor, just what you need on race day. That is if you make it to the starting line without an injury or screwed-up hormones. Food is also completely unenjoyable and takes valuable time out of our day for preparation. Nourishment is for the weak.

The reality: Within-day energy deficits and even longer energy shortfalls are common in the endurance athlete community. Low energy availability (LEA) is defined as a condition when energy expenditure is greater than energy intake. Chronic bouts of LEA can result in a higher risk of injury, illness, hormonal imbalance, and ability to adapt to training stressors.  It also is a risk factor for the development of REDs and eating disorders

David Roche talks more about these implications in his article about how within-day energy deficits can hurt health and performance, especially for female athletes. In order to avoid a LEA state, it is best to set up a consistent eating pattern for yourself and get a general sense of where your energy requirements and consumption are.. Getting help from a sports dietitian can help in this area if you are unsure how to figure out where you stand.

RELATED: Here’s How To Refuel After A Race For Optimal Recovery

Hydration is just an idea made up by “Big Run.” 

Let’s be real here: “Big Run” really only wants you to take in fluids as a ploy to control your fueling plan and sell you more hydration products. Hyper- and hyponatremia are made-up conditions and there’s no reason to figure out sodium sweat concentration. The real move is refraining from fluids and seeing if you can make it the whole race without full kidney damage. 

The reality: Insufficient fluid and electrolyte replacement during training and racing can impact your heart and kidney function. Taking in too little sodium is a potentially fatal condition if not addressed appropriately. To figure out your own hydration requirements, regular fluid loss testing combined with sodium sweat concentration testing is recommended.  



  1. Tiller, N.B., Roberts, J.D., Beasley, L. et al. International Society of Sports Nutrition Position Stand: nutritional considerations for single-stage ultra-marathon training and racing. J Int Soc Sports Nutr 16, 50 (2019).
  2. Zouhal, H., Saeidi, A., Salhi, A., Li, H., Essop, M. F., Laher, I., Rhibi, F., Amani-Shalamzari, S., & Ben Abderrahman, A. (2020). Exercise Training and Fasting: Current Insights. Open access journal of sports medicine, 11, 1–28.
  3. Cabre, H. E., Moore, S. R., Smith-Ryan, A. E., & Hackney, A. C. (2022). Relative Energy Deficiency in Sport (RED-S): Scientific, Clinical, and Practical Implications for the Female Athlete. Deutsche Zeitschrift fur Sportmedizin, 73(7), 225–234.

Kylee’s mission is to separate facts from fads in the endurance nutrition space and works to provide easy nutrition solutions to help improve health and performance. Kylee is the founder and owner of her sports nutrition business Flynutrition, which helps runners, triathletes, cyclists, and skiers to learn not only the ‘why’ but the ‘how’ behind fueling for performance. Her work has appeared in Trail Runner and Women’s Running Magazines.

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