Like a lot of new moms, I told myself the exhaustion was just part of it. The brain fog, the constant colds, the period that never came back. All easy to explain away when you have a baby in daycare and a full plate at work. I was doing the "right" things: moving my body, getting back to my routine, pushing through.
But I was likely running on empty — literally. I'd returned to work postpartum, was breastfeeding, and tend to eat less when the stress piles on. Exercise is my stress outlet, which meant I was burning more than I was putting in. My body rationed.
There’s a name for it. I still don't know for certain that it was RED-S. But a friend mentioned it to me and when I started digging into the research, I recognized myself in it. And I suspect some of you might too.
Can RED-S happen to women who aren't competitive athletes? Are you at risk?
You don't have to be an elite athlete
RED-S, or Relative Energy Deficiency in Sport, was originally framed around competitive athletes. But the 2023 IOC consensus statement makes it explicit: the framework applies to any exercising individual, regardless of competition level.
And the numbers suggest that many of us have probably experienced it:
45–63% of recreationally active women screen at-risk for low energy availability (LEA).
One US study found no meaningful difference in risk between NCAA athletes and recreational exercisers.
Only 22% of active women had even heard of the Female Athlete Triad1 — despite nearly half meeting risk criteria.
If you work out regularly and chronically underfuel — intentionally or not — your body can trigger the same cascade seen in elite sport.
What is underfueled? The 2023 IOC consensus frames it as a sliding scale: roughly 30–40 kcal/kg of energy available2 puts you at risk.
What your body is actually doing when it's underfueled
When you consistently burn more than you take in, your brain reads it as scarcity and starts rationing. Here's the chain reaction:
Key hormones drop: leptin, insulin, and thyroid hormone (T3) all fall
Cortisol rises: your stress hormone goes up
Reproductive signals get suppressed: LH and FSH — the hormones that drive your cycle — are dialed down
Estrogen falls: the result ranges from subtle luteal phase changes to no period at all
Two details worth knowing:
T3 suppression can show up within just 4–5 days of significant underfueling, making it one of the earliest measurable signs, and a key marker clinicians look for.
Timing matters, not just totals. Going long stretches with an energy gap around workouts, even when your daily intake looks fine, is independently linked to lower estrogen and higher cortisol.
Why it often goes unrecognized
RED-S is easy to miss. A few reasons why:
No single confirmatory test exists. It's diagnosed by pattern, not one number.
Symptoms overlap with thyroid disease, burnout, and PCOS.
It's frequently misclassified. Research suggests up to half of women diagnosed with a certain PCOS subtype (irregular cycles, no elevated androgens) may actually have functional hypothalamic amenorrhea (the hormonal endpoint of prolonged underfueling).
If you don't call yourself an athlete, you won't think to mention it. And your doctor probably won't ask.
Fortify Your Routine
🍽️ Today: eat something with protein and carbs within 60 minutes after your next workout. Large post-workout energy gaps, even on days when your total intake looks fine, are independently linked to lower estrogen and higher cortisol. Closing that window consistently is one of the most straightforward things you can do.
📅 This week: log your last three cycle lengths. Subtle changes (e.g., shortening below 24 days, irregular spacing) are early signs on the RED-S continuum. Logging three cycles gives you a baseline for future comparison.
🌡️ At your next doctor's visit: ask for free T3, not just TSH. Low T3 (with normal TSH) is an early metabolic marker of underfueling and can appear within days of a significant energy deficit. Bring up your exercise habits and eating patterns.
⏰ Tomorrow morning: eat something before a fasted workout. Fasted training extends the overnight energy gap. Even something small — a banana, a scoop of nut butter — shifts your energy balance and reduces the cortisol spike that follows working out in a deficit.
How valuable was today's issue for you?
1 The female athlete triad (the triad) refers to the combination of 3 clinical entities: menstrual dysfunction (like missing periods), low energy availability (with or without an eating disorder), and decreased bone mineral density (BMD).
2 When researchers study energy deficiency, they don’t look at the total daily calories that we consume. The look at energy availability (EA). This is what’s left over for your body to run on after you subtract what you burned in exercise. The formula is: EA = (calories eaten − exercise calories burned) ÷ kilograms of fat-free mass.
