Marathon Training, RED-S, and Weight Gain: Why I’m Choosing Fueling Over Shrinking
The uncomfortable truth about underfueling in runners, marathon culture, and redefining what strength actually looks like
When I trained for my first marathon, I had absolutely no idea what I was doing. My training plan was mostly vibes. I wore the same pair of Hoka Clifton 9s for every run, treated every workout like a tempo run, and hoped I could survive 26.2 miles without imploding.
Secretly, though, I wanted to break four hours. I finished in 3:50.
That race changed everything.
I fell hard into marathon culture. I signed up for the California International Marathon (CIM), joined a training group, and became obsessed with all the things distance runners eventually obsess over: fueling strategies, recovery protocols, race shoes, electrolytes, gels, workout structure, and optimizing performance.
I loved it, AND I couldn't help but notice some of the more harmful parts of endurance sports culture, especially the messaging around body size, performance, and what runners are “supposed” to look like.
When marathon training and underfueling catch up with you
Two weeks before CIM, I woke up after a long run barely able to walk because of severe glute pain. I panicked.
I rushed into physical therapy, did everything possible to make it to the starting line, and somehow still managed to PR by 10 minutes. Then I spent the next week on crutches.
After recovering, I started training for Twin Cities Marathon. This became my strongest training cycle yet. I increased strength training, prioritized recovery, improved my fueling, and focused heavily on core and glute stability.
Then, once again, two weeks before race day, the pain came back during a long run. This time, it radiated into my low back. I assumed physical therapy would help me push through again. Instead, I was referred to a pain specialist who suggested something I never expected to hear:
“You may have a sacral stress fracture.”
Then another possibility:
“Have you considered RED-S?”
What is RED-S in runners?
RED-S stands for Relative Energy Deficiency in Sport.
RED-S occurs when athletes do not consume enough energy to support both exercise demands and basic physiological functioning. Essentially, the body doesn’t have enough available fuel to sustain intense training while also supporting recovery, hormones, bone health, metabolism, and overall health.
RED-S in runners can affect:
bone density
hormone health
metabolism
recovery
mood
sleep
menstrual function
cardiovascular health
athletic performance
injury risk
Importantly, you do not have to be underweight to experience RED-S. That misconception causes real harm in endurance sports.
Why hearing “RED-S” hit me so hard
I’m an eating disorder therapist. I openly talk about fueling. I joke about carb-loading for races. At one point, I literally said I wanted to experiment with a two-week carb load “for science.” I genuinely thought I was eating enough. So, hearing that I still might be underfueling during marathon training felt deeply frustrating and honestly a little humiliating.
One of the biggest myths in both eating disorder recovery and endurance sports is that underfueling always “looks obvious”, but it doesn’t.
Sometimes underfueling looks like discipline. Sometimes it looks like optimization. Sometimes it looks like high performance. Sometimes it looks like just not being very hungry. Sometimes it looks like GI discomfort or honestly food intake fatigue. Sometimes it even looks “healthy.”
Marathon culture and the fear of weight gain
Distance running culture quietly reinforces the belief that lighter equals faster.
There’s constant conversation around:
race weight
body composition
leanness
optimization
shrinking your body for performance
And while body size is only one small factor in running performance, it often becomes emotionally overvalued in endurance sports.
Why I’m prioritizing fueling over shrinking this marathon cycle
I’m currently training for the Chicago Marathon, and mentally, this training cycle feels very different.
This time, I’ve made a deliberate choice: I would rather be overfueled than underfueled.
I don’t fit the stereotypical image people imagine when they think about RED-S or energy deficiency in female runners. But I care deeply about making sure my body has enough support to train hard, recover properly, rebuild tissue, and stay healthy long term. That may mean my body changes, and I might gain weight while fueling my body.
And I’m trying very intentionally to believe that gaining weight is a good thing, because a body that is adequately fueled is not a body failing. It’s a body being supported.
Distance runners normalize extraordinary things
One of the strangest things about long-distance running is how quickly huge accomplishments start to feel normal.
Two years ago, running any mileage longer than 13.1 felt like a lot. Now it feels casual.
Two years ago, finishing a marathon felt enormous. Now I’ve cut more than 20 minutes off my marathon PR.
Somewhere along the way, I stopped being impressed with myself because I kept moving the goalpost. I think a lot of runners do this. We become so focused on pace, splits, PRs, and optimization that we lose perspective on how extraordinary our growth actually is. My friend, Shanon, always says, “we need to remember that what we do isn’t normal!”
My body has carried me through:
thousands of training miles
injuries
recovery
disappointment
rebuilding
resilience
That deserves respect and celebration!
Redefining strength beyond thinness
As both a runner and an eating disorder therapist, I keep coming back to the same question:
What happens when we stop equating thinness with worth — even in endurance sports where thinness is constantly normalized?
What if strength looked like:
adequate fueling
recovery
flexibility
body trust
sustainability
enoughness
What if health was measured by capacity instead of control? What if weight gain during marathon training wasn’t automatically viewed as something negative?
I don’t fully have the answer yet as I’m still working through this in real time. What I do know is that my goal this season is not just to finish another marathon or even solely to PR (I do want to PR, just to be clear). But, the main goal is to build a relationship with my body that can actually sustain and support endurance running, and I think that starts by giving my body more rather than demanding that it become less.
