5 Signs You May Be Underfueling – Feetures

5 Signs You May Be Underfueling

5 Signs You May Be Underfueling

One of the biggest mistakes I see in runners of all levels is improper fueling. When it comes to running, improving your nutrition is one extremely effective way to optimize your performance. I only started to see massive PR’s and strength gains once I was fueling my body ENOUGH to support my marathon training, and in practice I see many already high level runners limiting themselves by how much they AREN’T eating. Chronic underfueling can lead to a condition called Relative Energy Deficiency in Sports, or RED-S. Commonly referred to as the Female Athlete Triad in the past, this new title makes the condition applicable to the entire gender spectrum, as underfueling has negative consequences for males and females (Ref 2)

Let’s use a metaphor to elaborate on this. Say you’re a car. Cars need gas in order to get anywhere no matter the type of car. Some cars may be more fuel efficient than others, but as a general rule, all cars need fuel to drive distances. Runners are the same way! We all need adequate nutrition in order to run distances. While some of us may be faster than others, all of us still need adequate fuel. Furthermore, the type of fuel you put in the car also matters, because we all know what happens when you put the wrong fuel into a car. It just doesn’t run as well as it should.

Now say you aren’t putting enough gas in the tank. If you only put in 50 miles worth of gas, how can you ever expect the car to make a 100 mile trip successfully? Runners and individual fueling needs follow the same rules. If you are wondering how to know if you are fueling your exercise adequately, these five signs listed below may help you decide if you need to up your fuel game or talk to a registered dietitian to come up with an appropriate plan for you.

You are bonking or hitting the wall during your workouts, not recovering from them well, or experiencing frequent injury.

Running is hard. Running hard for a long distance is even harder! While your runs and workouts are designed to challenge you so that you get stronger, fitter, and faster, you should not be completely exhausted during or after every single effort. If you are noticing especially that your runs or efforts that felt easy in the past are feeling really difficult, you may want to consider looking at your nutrition.

The human body runs on calories for energy, and if it is not getting enough to support itself without involving physical activity, you really can’t expect it to perform well during any kind of exercise. Exercise is extremely stressful on the body, and you will only reap the benefits of the exercise you are doing if you are fueling yourself properly and recovering from your workouts adequately. Even 300-500 calories below your needs per day can negatively affect your health and performance as an athlete. (Ref 2)

You are feeling tired all the time, but also can’t seem to get enough sleep.

Oh the frustration! As mentioned above, running is hard, but an appropriate amount of exercise combined with appropriate fueling and adequate recovery strategies should actually leave you feeling more energized and not more tired. Here’s why: when we exercise appropriately, our bodies create more powerful and efficient mitochondria in our cells with each muscular contraction from physical activity. Mitochondria are like the battery pack of the cell, so having more efficient batteries, by default, gives us more energy. (Ref 3)

We require energy to run, to repair our body from stress created while running, and to build more muscle mass and keep our current body tissues healthy. We also require energy just to exist- this is called your basal metabolic rate (BMR).

If you are exercising without enough fuel in the tank consistently, your body will actually respond by destroying its own muscle tissue to use for energy. If you are eating enough, your body will use the nutrients and calories in food for energy instead to do all the amazing things discussed above. So if you are feeling tired all the time despite exercising (which is supposed to give us more energy), you might want to reconsider your nutrition plan.

When our bodies are stressed from exercise and also stressed from not having enough fuel to help us recover from that exercise, it can have negative effects on our sleep (Ref 4). Exercise is a stressor on the body, as is inadequate nutrient and energy intake. When we are extra stressed from these things, or from sitting in traffic, or in caveman times when we encountered a saber-tooth tiger, our body releases a stress hormone called cortisol. Cortisol triggers the “fight or flight” response in our nervous system, allowing us to run away from the saber tooth tiger. Once we have safely outrun the saber-tooth tiger, our cortisol levels drop and we can return back to normal life.

The problem is that in modern day, a lot of us are stressed all day long. When this happens, we continue to release cortisol and trigger that fight or flight response, making it really challenging for us to sleep well. Constantly underfueling our workouts is similar circumstances to the body as encountering a sabertooth tiger.

Our body only knows stress as stress - and something has to give eventually. If you are going through a long period of time without sleeping well, many things could be attributing to this, but one thing to look at could be your nutrition habits and stress management strategies (or maybe lack thereof!).

Your hair is thin and brittle, and you are feeling cold frequently. In females, you may lose your menstrual cycle, experience menstrual irregularity, hormone imbalance, and low libido. In males, you may experience low libido. 

No amount of hair skin and nails supplements can fix brittle hair if you are not eating enough calories in general. When your body is under any kind of stress,  like putting it through running or not feeding it enough or both, it will start to shut down various processes and systems that are not essential to keep you alive.

This can include brittle or thinning hair, skin or nails that lack their normal integrity, and shunting blood to your core where your organs are to keep them working instead of your extremities. Oftentimes runners who feel that they have Raynaud’s Syndrome experience an improvement in symptoms of cold extremities once they are eating adequate calories overall.

In females, irregularity in their menstrual cycles or missing periods completely is a red flag for hormone related issues, which can be a result of underfueling. In males, low libido is a similar red flag. In one study at the 2016 Olympics including elite endurance athletes, it was found that the risk of developing a stress fracture was 4.6 times greater in females who missed their periods or men with lower testosterone levels. (Ref 1)

Chronic underfueling can lead to hormonal shifts associated with bone density issues down the road- and no runner ever wants to be sidelined with a stress fracture or bone injury.

You’re thinking about food often, having intense sugar cravings, or feel the need to eat large portions of food, usually in the afternoons or evenings.

As a dietitian in practice, I see this happen all the time. Runners- or anyone for that matter- who think they need to watch what they eat and try to be “good” for the first part of the day only to find themselves several cookies or bags of chips deep in the afternoons and evenings need to consider improving their nutrition habits and overall relationship with food.

If you are not feeding your body enough throughout the day and putting it into an energy deficit by running or exercising, your hormones and biology are perfectly wired to hit you hard with cravings for simple sources of carbohydrates to make up for lost calories.

Your body is so good at surviving, and one of its many talents is preventing you from dying via famine- whether this is self-induced famine or not. A calorie deficit is a famine, according to your body. Whether you’re doing this on purpose, accidentally, or have no control over when your next meal will be, your body is going to fight hard to get you to eat anything lying around for quick energy to keep your brain alive.

You are losing or gaining weight.

While not everyone experiences this who is underfueling, many runners may experience weight loss or even weight gain. This is the body’s response to inadequate calories or imbalance of nutrient intake. It will either start burning its muscle mass and fat for energy due to lack of adequate calories coming in from food, or in many people- especially females- the body will actually burn its muscle tissue for energy and store anything you do eat as fat to “protect” you from famine like we talked about earlier. 

If any of these points resonate with you, reach out to a registered dietitian to evaluate your eating habits. Underfueling can have some serious long term consequences, and if you want to have a long, successful running career it is so important to be just as good at eating as you are at running! Eat to run - not the other way around. Working with a dietitian who specializes in helping runners fuel to perform and feel their best can be just the key sometimes to get you your next personal best time!

Woman running down the sidewalk

Holley is a registered dietitian nutritionist, certified personal trainer, and owner of her private virtual nutrition and fitness coaching practice, Fit Cookie Nutrition LLC. She specializes in helping all levels of runners train for races, develop a healthy relationship with food and body image, and fuel themselves for optimal performance both in running and life in general.

To learn more visit https://www.fitcookienutrition.com/ or send her a message at [email protected]


  1. Heikura I, Uusitalo A, Stellingwerff T, et al. Low energy availability is difficult to assess but outcomes have large impact on bone injury rates in elite distance athletes. Int J Sport Nutr Exerc Metab 2018;28(4):403-411.
  2. Mountjoy M, Sundgot-Borgen J, Burke L, et al. The IOC consensus statement: beyond the Female Athlete Triad--Relative Energy Deficiency in Sport (RED-S). Br J Sports Med.2014 Apr;48(7):491-497.
  3. Oliveira, A. N., & Hood, D. A. (2019, September 25). Exercise is mitochondrial medicine for muscle. Retrieved May 20, 2020, from https://www.sciencedirect.com/science/article/pii/S2666337619300083?via=ihub 
  4. St-Onge, M.-P., Mikic, A., & Pietrolungo, C. E. (2016, September 15). Effects of Diet on Sleep Quality. Retrieved May 20, 2020, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5015038/ 

Written by

Blue Corona

Leave a comment

Please note, comments must be approved before they are published

← Back to The Run Down