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When your car is low on gas, you have two clear warning signs.
Jacob Lund/Adobe Stock
First, your gauge edges ever closer to E. Then, if you keep pushing, youll stall.
But our bodies are much more intricate machines.
Underfueling is more common than you may thinkand you might not know youre doing it either.
Over time, this can progress into a condition called relative energy deficiency in sport, or REDs.
Dont let the word sport in the name throw you off.
While these conditions are common among elite and pro athletes, everyday exercisers can absolutely develop them.
Even far more casual runners, cyclists, and gym-goersanyone whos activecan underfuel too, McConville says.
And this holds true for folks of all body sizes.
Underfueling doesnt necessarily have to be intentional either.
To understand why, think of your body more like a bank account than a car, McConville says.
Each time you eat, its an investment.
Everything you do throughout the day, including your workouts, requires a withdrawal.
Thats why knowing underfueling is possible, and staying alert for red flags, is important.
Here are 15 ways to know you might be running on low.
Your mood is tanking, and youre not sure why.
A few minutes of doomscrolling these days can easily make you anxious or sad.
If we are hungry, we arecranky, a.k.a.
You think about food a lotbut often cant make up your mind about what to eat.
You tend to go on binges later in the day.
Similarly, underfueling can kick off a vicious cycle: You skimp on fuel through breakfast and lunch.
By mid-afternoon or evening, youre famished enough to demolish your snack drawer.
You feel bad, restrict yourself again the next day, then repeat.
Not only does this not feel great in the moment, you may worsen some of the other consequences.
Read: Theyll feel pretty good and not notice many of these symptoms.
Each workout feels way harder than it should.
And you drag much more than usual afterward.
Yes, hard effortsthink long runs during half or full marathon trainingcan leave you feeling fatigued.
In fact, youd rather just bail on the gym altogether.
Even the most elite athletes have days when theyd rather not train.
Tune into what your thoughts are saying, Roth-Goldberg says.
If its a constant, This feels so hard.
Why am I doing this?
This is not fun, that is a sign of low energy.
Your gut rumbles way more than it used to.
The experience can resemble irritable bowel syndrome (IBS), McConville says.
This, too, can kick off a harmful cycle.
Meanwhile, your hormones and vitamin levels are all out of whack.
Bloodwork you get at the doctor may also show abnormalities of certain vitamins and minerals.
And merely popping a multi wont correct the issue, because underfueling also decreases the absorption of key nutrients.
As a result, your iron tests can come up low.
You may also noticeabnormal levelsof thyroid-related hormones, including thyroid stimulating hormone (TSH) and free T3.
That should be viewed as a warning sign.
Your heart rate falls, while your cholesterol levels rise.
Conventional wisdom holds that eating less = shrinking your body.
In addition, abnormal levels of thyroid hormones could leave you feeling unusually chilly.
Thats why people who are underfueling might becold all the time.
Your hair and skin might suffer.
You get hurt more often, and healing takes longer.
Bone injuries have long been linked to disordered eating and eating disorders, especially in women.
But increasingly, sports medicine experts recognize that underfueling can contribute to other issues too.
Youll likely heal more slowly when you do get hurt too.
Waitthis makes me realize I might be underfueling!
What should I do about it?
Noticing a potential problem is a huge first step.
Treatment involves rebalancing by eating more, exercising less, or both.
But although it can be hard to break existing habits, the payoff is more than worth it.
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