Why Underfueled Athletes Can Feel Faster
By the time that Max came to see me, he had been deeply ingrained in his nutrition habits.
He was a competitive college athlete with high level aspirations, yet he knew his nutrition wasn’t sustainable. At the same time, when his last season ended, he noticed changes in his body and was worried if he started eating enough, he would continue gaining weight.
He also had a hard time eating before practice. Every time that he did eat, he would feel foggy, slow, sluggish. The times that he didn't eat, he had a sense of sharpness, attention, and focus.
To him, even though there was this gap between what he felt like he should be eating, and what he was currently eating, he knew that when he had tried to eat more, it had slowed him down.
And he thought that continuing to eat more and eat enough would mean that he would lose some of his line speed, sharpness, and edge on the field.
As a sports RD, I’ve noticed this challenging spot that athletes find themselves– they may acknowledge that their current approach isn’t sustainable, but they feel stuck because when they’ve tried to change it in the past, they’ve wound up frustrated and no further ahead.
There is a very real conundrum of feeling like performance is improving while simultaneously running on empty.
We must talk about this phenomenon because it’s one of the biggest reasons athletes rule themselves out of having low energy availability: they don’t feel bad. Their training doesn’t necessarily feel worse. They may feel quick. They may feel focused, more prepared even.
But when you look underneath the surface, there is a slow erosion of their foundation that, unaddressed, might lead them further down a rabbit hole that’s harder to dig out of.
The truth of REDs often missed: athletes may feel good. That is, until they don’t.
Because by the time the cracked foundation starts to spiderweb up, they may now be dealing with significant sleep disruptions, GI symptoms, a bone stress injury, or being chronically sick. And now, their minor injuries compounding, athletes are wondering where things suddenly went wrong. They didn’t see it as a problem because they were waiting to drop off a cliff. Now it’s likely a more prolonged recovery than if identified in the early stages.
What Happens When Athletes Feel Better When They Don’t Eat
Let’s break it down:
There is some truth to the idea that there may be an advantage to being a little hungry.
Think back to our hunter-gatherer ancestors– if you can’t hunt down your lunch, you might not survive. You need to be able to mobilize, especially when you’re a little hungry.
Evolution blessed our physiology with this exact mechanism.
When the body experiences stress, it mobilizes resources and sends stress hormones like catecholamines to respond to an immediate demand.
This is an incredibly useful system that allows us to be alert and make quick decisions to get your next meal or else you might compromise survival.
This is likely what is happening when athletes say they feel sharper or runners feel faster when they’re fasted. I won’t deny their reality, but we also must look at the potential cost of relying on this strategy long term.
Robert Sapolsky’s Why Zebras Don’t Get Ulcers paints the picture of what a system under chronic, unrelenting stress looks like.
Sapolsky states that while a Zebra might have its survival threatened and its flight or fight response activated, the threat will resolve and the zebra will return to baseline. In humans, it’s often a low level, chronic stress present that negatively impacts health.
The response itself isn’t necessarily bad; it’s the lack of opportunity to recover from it.
It’s not physiologically healthy to be fighting for your life on a near-daily basis.
Further, athletes can end up chasing this feeling because they believe it’s performance-enhancing. They come to rely on it as an indicator of success.
When we look at the training loads of athletes, I can’t help but wonder: what is the secondary impact of not only the stress of training, which we consider to be a positive, adaptable form of stress, compounded with the metabolic and physiologic stress of being under-resourced and relying on the fumes of fight or flight to focus?
Training is a stressor.
So is inadequate energy availability.
And if you only have capacity for so much, who decides where feeling good ends and being burnt out starts?
Are Feeling Sharp and Being Sharp the Same Thing?
Consider a parallel in cognitive literature: Students without ADHD were administered the stimulant medication Adderall, commonly abused as a study aid, and completed a series of cognitive tests.
While the students reported they felt their focus and concentration improved, this did not reliably predict performance on objective tests[1].
While beliefs and expectations can be powerful, it’s also important to take a step back and question whether the health risk of chronic energy deficiency is worth the perceived trade-off.
A systematic review of 59 studies showed low energy availability was correlated to decreased performance in just about every area: run performance, training response, endurance, coordination, concentration, judgment, explosive power, and agility, as well as worse attendance related to illness[2].
Even if underfueled athletes “feel” sharper, the evidence at scale suggests otherwise.
So… Why do I feel like crap when I eat?
This is another fascinating response.
It’s likely that it’s a combination of two things:
One, that GI systems are both adaptable and can be compromised in a chronic low energy state. When exercise is added to the equation, one may struggle to digest fueling snacks as blood flow shifts towards working muscles and the lungs. Under ordinary circumstances, the GI system may need to be trained to incorporate fueling around training.
Two, eating may shift the nervous system towards a “rest and digest” state. In contrast with the jittery, adrenaline-fueled rush, it may be interpreted by the athlete as foggy, sleepy, or slow.
In both situations, it can take time and good fueling practices during the other hours in a day to restore tolerance to fueling closer to training and athletes may benefit from simple to digest or sports drinks with carbohydrates to ease into pre-training fueling. They may need some tweaking of timing to find a “sweet spot” for including fuel rather than avoiding it entirely.
The needed shift:
Breaking out of this pattern takes time, patience, and a willingness to experience discomfort. Thankfully, athletes tend to have these traits in spades. The hard part is being open to the mindset shift towards knowing that there is often a gap between what feels like the best thing for performance right now and what will support long-term sport participation and health.
Most athletes would not willingly agree to set themselves on fire to have one really good season just to have to retire by the next.
Yet when athletes are relying on the stress response and underfueling to maintain a lighter physique, this is part of what is happening.
The body becomes a resource to be consumed, a bicycle ridden until the wheels fall off.
For many reasons, but I’ve surmised for many that it’s based on the feeling that depletion and exhaustion is evidence that they are doing enough.
But if you want to be around to see what your body is capable of?
You have to fuel it.
You have to give it a chance to adapt.
You must fuel the long game.
As for Max?
While he found discomfort, as many do, in learning to match fueling to training, he noticed that while at first he was reluctant to let go of the empty feeling of focus he described, the new focus he discovered was different.
He found himself feeling more centered, confident, and at ease. He could actually drop into flow during games and wasn’t experiencing adrenaline crashes throughout the week.
He didn’t end up losing his edge. Instead, he found a more sustainable way to access it.
note: while Max is based on the experiences of several athletes, details have been changed to protect client confidentiality
References:
[1] Ilieva I, Boland J, Farah MJ. Objective and subjective cognitive enhancing effects of mixed amphetamine salts in healthy people. Neuropharmacology. 2013;64:496-505. doi:10.1016/j.neuropharm.2012.07.021
[2] Gallant TL, Ong LF, Wong L, et al. Low Energy Availability and Relative Energy Deficiency in Sport: A Systematic Review and Meta-analysis. Sports Med. 2025;55(2):325-339. doi:10.1007/s40279-024-02130-0
