Female Endurance Athlete Fueling Strategies to Avoid Relative Energy Deficiency in Sport (RED-S)
What female endurance athletes should know about their fueling
You can train hard and eat super “clean” and unknowingly be sabotaging your performance.
It’s easy to fall into a trap of underfueling and/or overtraining, especially as recreational runners, when you’re leading a busy life and trying to eat super healthy while often coping with high stress by exercising. However, a condition called Relative Energy Deficiency in Sport (RED-S) demonstrates the risks of mismanaged nutrition and training, which can ultimately lead to issues in your performance and longevity.
This isn’t just a condition that impacts elite athletes, there are studies (1) estimating up to 60-80% of female endurance athletes could be facing RED-S. Yet, despite the prevalence, RED-S often goes unrecognized, which can lead to increased injuries, performance declines, and even compromised hormonal and bone health. So here’s what every female runner should know.
The “Performance Paradox” – Why underfueling can be an unintentional slippery slope
Oftentimes, RED-S can develop as a slippery slope. Especially within endurance sports, where there can be an expectation or false belief that being smaller or leaner is always better, we may develop habits with the intention to be lean, fit, or “healthy”.
And initially, we’re often praised for having more “discipline” or noticing changes in our body, and we aren’t privy to the long term effects of these lifestyle habits. Additionally, the culture of “pushing through” and training harder in order to improve our performance can distract us from the root issue.
In reality, studies (2) show workouts can start feeling harder after just a few days of glycogen depletion. If it progresses to a state of chronic underfueling, then we risk further negative health consequences, including reductions in bone density, disrupted reproductive functioning (like missing periods), and even mental health impacts like low mood, irritability, or chronic stress.
RED-S Warning Signs and Symptoms
It can be really valuable to catch early signs and symptoms of RED-S in order to address the issue before it turns into something more serious. According to this study (3), these are a few questions you should answer to assess your own risk for RED-S:
Are you experiencing irregular or missing periods?
Do you have mood changes like irritability, anxiety, or depression?
Have you had more than one injury in the past year?
Do you experience poor sleep or constant fatigue?
Has your athletic performance stagnated or even declined unexpectedly?
If you said yes to two or more of these questions, it could be time to seek support from a healthcare professional along with diagnosis and treatment options.
What is the “Clean Eating” trap?
Most women don’t think they’re underfueling because they believe they’re just eating “healthy”. Yet, there are several recent diet trends that could be increasing the likelihood that women are adopting behaviors that are causing RED-S.
In addition to some of the symptoms outlined previously, here are some of the common behaviors patterns that are frequently seen in folks struggling with RED-S:
Training fasted
Skipping snacks or eating less on rest days
Demonizing food groups, like avoiding bread, pasta, or “oily” foods
Feeling guilty for taking days off or cutting back on exercise
3 Simple Ways to Prevent RED-S
1. Make pre-run fuel a non-negotiable. (even if you're not hungry, suggests this study (4) ) Introducing a pre-workout snack, especially if you’re exercising in the morning, can not only improve your energy availability to prevent RED-S but also improve your performance, fitness, and recovery.
2. Eat before you're starving. Sometimes we attribute hunger with purely physiological hunger, and we can “forget” to eat or ignore subtle signs of hunger, like thoughts or fixation on food. Eating snacks throughout the day can be key and often requires challenging the pre-existing standards we have around hunger levels.
3. Focus on adding more vs restricting. Particularly for active women, it’s common that we’re undereating on certain macro groups, especially the ones that are demonized in diet culture. However, we need to make sure we’re eating enough in all categories, otherwise our bodies can perceive that we are in a state of underfueling.
The Takeaway: Why This Matters Beyond Training
RED-S isn’t just about performance or nutrition for your next race—it affects bone health, fertility, mental clarity, and long-term energy. Many women don’t recognize the impact until they hit burnout, injury (like stress fractures), or chronic fatigue. But in reality, RED-S and its health risks are 100% reversible when caught early.
If you’ve been second-guessing your fueling, feeling more tired than usual, or stuck in cycles of burnout when it comes to stress and/or exercise, it might be time to shift your approach.
To get started, check out the resources offered at Koa Athletic Health, an interdisciplinary team that provides support for preventing, managing, and recovering from RED-S for active women.
References:
(1) - https://bjsm.bmj.com/content/57/17/1073
(2) - https://bjsm.bmj.com/content/53/10/628
(3) - https://pubmed.ncbi.nlm.nih.gov/38956804/
(4) - https://pubmed.ncbi.nlm.nih.gov/29205517/
Allison Yamamoto, REDs & HA expert
Guest Blogger
Sports Nutrition Coach & Run/Cycling Instructors
CEO & Founder of Koa Athletic
Founder & Coach at Ally
Bio: Allison is a RED-S and HA expert with a deep interest in women empowerment, running, technology, menstruation, and mental health.
She is the Founder/CEO of KOA Athletic Health and Founder & Coach at Ally, where she helps active woman ditch under fueling and overtraining to regulate their period and feel free around food and exercise.