When it comes to RED-S symptoms in athletes, I often hear these two statements…
“I’m still eating, so I can’t have RED-S.”
“I haven’t lost weight, so I can’t have RED-S or be underfueling.”
Many athletes think these are “unexplained” symptoms and are skeptical to believe they are related to nutrition and underfueling. Whether due to a lack of awareness or the deep-rooted weight bias in sport culture and our society, many athletes incorrectly assume underfueling is only a problem for those who are visibly or severely underweight.
But that’s simply not true.
In this blog post, I’m breaking down how underfueling in athletes can cause RED-S symptoms, even without weight loss or being underweight.
No Level of Underfueling in Athletes Is Insignificant
As you’ve probably heard me say many times before, no level of underfueling in athletes is insignificant. That is not just my personal opinion, it is well supported in research.
As little as a 250-400 calorie deficit over 5 consecutive days can result in symptoms of relative energy deficiency in sport (RED-S).
This could be as little as skipping your typical afternoon snack, slightly reducing your meal portions, or adding a couple extra miles to your daily training during the work week.
RED-S Symptoms from Acute Underfueling
Some of the physical and performance-related symptoms that may result after a period of acute underfueling may be brushed off or misunderstood. However, they are key signals your body is under stress.
These RED-S symptoms include (but are not limited to):
Physical symptoms of acute underfueling:
- Impaired digestion
- Change in mood
- Menstrual cycle disturbances
- Sleep disruption
- Lowered heart rate
Performance related symptoms of acute underfueling:
- Trouble focusing
- Increased irritability
- Increased soreness
In an ideal world, these symptoms would be enough of a signal for athletes to recognize and correct this mismatch in their energy expenditure versus their energy intake. However, I have found that many athletes either at first don’t correlate these symptoms with a lack of nutrition (e.g., impaired digestion, trouble focusing, disrupted sleep) or they view these symptoms (menstrual cycle disturbances, lowered heart rate) as signs of fitness.
Because of this, I typically don’t see athletes until they have been in a much more long-term, chronic state of underfueling, which unfortunately means more severe symptoms, a longer period of recovery, and more time away from sport or unable to train at their full potential.
Long-Term RED-S Symptoms From Chronic Underfueling
When left unaddressed, chronic underfueling in athletes can result in more serious physical and performance-related RED-S symptoms.
These RED-S symptoms include (but are not limited to):
Physical symptoms of chronic underfueling:
- Stunted growth
- Bloodwork abnormalities
- Sleep quality
- Bone health
Performance related symptoms of chronic underfueling:
- Decreased endurance
- Decreased VO2 max
- Increased injury risk
- Decreased power vertical
Why Many Athletes Miss These Warning Signs
The tricky part? These RED-S symptoms don’t always “feel” like underfueling in athletes.
Athletes may think that disrupted sleep or digestion is due to stress, see a lower heart rate as a sign of fitness, or accept missed periods as “normal” in sport.
But these signs are often your body’s SOS signal for more fuel, not less.
Don’t Wait for a Diagnosis, Fuel Proactively
If you suspect you might be underfueling, even just a little, it’s worth addressing.
Remember: You don’t have to be underweight or losing weight to have RED-S. You just have to be underfueled.
If you’re an athlete ready to get out of the RED and fuel your strongest season yet, join the waitlist for my upcoming Athlete Nutrition Challenge, where I’ll give you the training, tools, and guidance to fuel smarter!
If you’re an athlete provider (think… coaches, RDs, and healthcare providers) looking to confidently identify and support athletes experiencing RED-S symptoms and underfueling, join my RED-S Informed Provider Masterclass, where I’ll take you through a deep-dive into screening, support, and science-backed strategies to support athletes.