How Underfueling Creates More Stress

The life of an athlete is filled with numerous mental, physical, and emotional stressors. In addition to the added stress of sport, athletes are still humans who have jobs, school, bills, families, friends, health, and so much more to worry about. A common analogy I use with clients is the stress bucket. Everyone has a stress bucket, and everyone’s bucket has a different capacity and durability. Because stress limits performance, it is advantageous to limit the number of things in one’s stress bucket and/or limit the size of each thing in the bucket to prevent it from overflowing. 

As a dietitian, I would be remiss if I did not mention the power that nutrition has to either help manage stress or contribute to stress. I have seen several clients weaponize nutrition through restriction in an attempt to quickly improve performance, change body composition, or even deal with life’s other stressors, ultimately being the many drops in the bucket that causes it to overflow. In this blog post, I will be discussing the consequences of stress on athletic performance, how underfueling athletic performance contributes to stress, and how to avoid falling into the trap of underfueling so that you can keep your stress bucket from overflowing.

How Stress Impacts Performance

In today’s culture, there is a tendency to minimize the effect that stress has on us as people. It is normalized to allow stress to build up until we have a self-proclaimed “mental breakdown,” laugh it off, and  shortly after return to our old habits only repeat the cycle again and again. There seems to be a perception that we can train our tolerance to stress so that each stressor shrinks and takes up less space in our bucket. There is also a perception that stress is necessary to get where you want to be in life and sport. While it is true that moderate amounts of stress increase motivation and improve performance, chronic stress and a lack of coping mechanisms ultimately lead to anxiety, depression, burnout, and ultimately poor performance.

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When pressure is too high or too low it has negative effects on performance.¹

Burnout is associated with withdrawal, reduced self-efficacy, and loss of athletic identity.² Chronic stress is also associated with elevated cortisol levels. Cortisol impacts blood sugar regulation, increases inflammation, and dysregulates sleep patterns.³ All three of these downstream effects of cortisol are absolutely essential to peak performance and recovery, and when these processes are dysregulated, they add to the stress bucket, making the athlete more susceptible to injury, burnout, decreased performance, and even life-long health implications. 

How Underfueling Adds to Stress

Obviously nutrition is absolutely essential for all humans, not just athletes. Unfortunately, many athletes subscribe to the misguided adage that “smaller is faster.” In fact, up to 94% of athletes competing in weight-sensitive sports report extreme dieting to achieve a target weight before competition.⁴ Moreover, this adage is reinforced by the fact that in the initial stages of dieting or restriction, times oftentimes do drop. But then they stop dropping, and everything feels more difficult, leaving the athlete wondering what they are doing wrong and striving to shrink their bodies further. 

Obviously, underfueling has a lot of physical effects on the body, but let's first focus on the mental effects, as these also impact the body’s physiological responses. When the body is in a state of low energy availability, caused by putting less fuel in than is required for the amount of energy demands being placed on the body, it triggers the so-called “cave person brain.” The cave person brain developed as a way to motivate humans to hunt and gather food long before we could just drive to the grocery store for it. When the body is in a state of starvation, it triggers the brain to become nervous, anxious, rigid, and defensive as a protective mechanism.⁵ 

A starved brain is never allowed to “rest and digest” and remains in a state of “fight or flight” thanks to the constant activation of the sympathetic nervous system. For someone who has significant distress around food, this fight or flight response is heightened around meal times.⁵ Our body senses this anxiety and diverts blood away from our digestive tract (where we want it when we are eating) toward our arms and legs (in preparation to flee the scene). This shunting compounds the distress of eating by oftentimes making meals and snacks even more difficult to physically and mentally tolerate by causing diarrhea, gas, bloating, malabsorption, and/or constipation. You can imagine that the physical discomfort brought on by not eating enough perpetuates the mental struggle of trying to eat enough. Not to mention, a stressed out gut is not going to promote a comfortable sporting experience. I know I have added minutes to my marathon races after making pit stops in the porta-potties along the course, turning what was at one minute a fun day into a miserable fight to the finish.

So you can see how the emotional side of eating affects digestion, but it also affects actual sport performance. Not only does activation of the cave-person brain trigger an anxious response, it causes the body to conserve energy by slowing down metabolic processes, as alluded to above.⁴  Some of the consequences include:

• Slowed down heart/respiratory rates

• Cognitive decline

• Muscle loss

• Maldigestion (diarrhea, malabsorption, constipation, bloating, gas)

• Reduced blood flow to extremities (cold hands & feet!)

• Decreased hormone production (amenorrhea, decreased sex drive)

• Decreased bone density (helllooo stress fractures and injuries)

• Slowed recovery⁵

These are just some of the effects that immediately impact performance and do not include those other stressors that impact long-term health (increased cholesterol levels, altered liver and kidney function, reduced reproduction capacity, decreased immunity).⁵ Aside from the obvious fact that the fuel input is not matching the output (you would not expect a car to be able to make a cross-country road trip with a half-tank of gas), these metabolic adaptations make meeting the high performance demands that athletes often set for themselves that much more challenging. The heart is weaker so it cannot reach peak output; muscles lose strength so they cannot lift as much or sustain activity as long. 

Health Consequences of Relative Energy Deficiency in Sport⁶

Physically, this feels awful. Emotionally, it feels worse. Much of the time athletes believe that cutting out certain foods and eating less or losing a little bit of weight will improve performance. We know that this is not the case long term. So, when a driven athlete’s performance starts to tank, they question what they are doing wrong, restricting more, pushing harder, and eventually getting injured and burning out. You can imagine what this does to self-confidence and identity (as many athletes’ identities are tied to their performance). 

This may sound dramatic and ominous, but anyone who has lived in a state of low energy availability or developed RED-S knows that it is a deep hole to pull yourself out of. The good news is that there is an easy fix: EAT MORE FOOD! 

Using Food to Empty Your Bucket

Unlike what social media will tell you about nutrition, nutrition needs are highly individualized. The great equalizer however is that all people need to eat enough. There are general guidelines we can use to help get to that place. For many athletes, this includes eating every 2-3 hours, incorporating carbohydrates at all meals and snacks, balancing larger meals with carbs, protein, fat, and fiber, and trusting your body’s signals of hunger and fullness. Consistent nutrition helps our bodies feel safe and regulated so that we can take on life’s stressors without feeling overwhelmed. Nutrition should function as the little faucet at the bottom of your bucket that can prevent it from overflowing, not the firehose dumping water into it.

If you are feeling overwhelmed by nutrition and would like more specific guidance, working with an RD can take some of the pressure off. Different athletes have different energy demands that are far beyond the scope of this blog post. You don’t have to balance it all alone. Book with a SkimWellness RD today!

1. Lopez Blanco, C., & Tyler, W. J. (2025). The vagus nerve: a cornerstone for mental health and performance optimization in recreation and elite sports. Frontiers in psychology, 16, 1639866. https://doi.org/10.3389/fpsyg.2025.1639866

2. Tossici, G., Zurloni, V., & Nitri, A. (2024). Stress and sport performance: a PNEI multidisciplinary approach. Frontiers in psychology, 15, 1358771. https://doi.org/10.3389/fpsyg.2024.1358771

3. Cleveland Clinic. (2025, February 17). Cortisol: What it is, function, symptoms & levels. Cleveland Clinic. https://my.clevelandclinic.org/health/articles/22187-cortisol

4. Sundgot-Borgen, J., Meyer, N. L., Lohman, T. G., Ackland, T. R., Maughan, R. J., Stewart, A. D., & Müller, W. (2013). How to minimise the health risks to athletes who compete in weight-sensitive sports review and position statement on behalf of the Ad Hoc Research Working Group on Body Composition, Health and Performance, under the auspices of the IOC Medical Commission. British journal of sports medicine, 47(16), 1012–1022. https://doi.org/10.1136/bjsports-2013-092966

5. Gaudiani, J. L. (2019). Sick enough: A guide to the medical complications of eating disorders. Routledge.

6. Mountjoy M, Sundgot-Borgen J, Burke L, et alThe IOC consensus statement: beyond the Female Athlete Triad—Relative Energy Deficiency in Sport (RED-S)British Journal of Sports Medicine 2014;48:491-497.