Bone health / energy
RED-S and stress fractures
Relative Energy Deficiency in Sport (RED-S) happens when training outpaces fueling — intentionally or not. The older term Female Athlete Triad (low energy, menstrual dysfunction, low bone density) describes part of the same picture and is still used in some medical settings.
Lost or irregular periods, persistent fatigue, frequent illness, or recurring bone pain — often alongside training hard and eating too little.
Signs to watch for
- ·Hair thinning or increased shedding
- ·Feeling cold when others don't (cold intolerance)
- ·Mood changes, irritability, or low motivation
- ·Poor sleep quality despite being exhausted
- ·Slow recovery between runs — legs feel heavy for days
- ·Stress fractures or bone pain that worsens with impact
How to avoid
- ·Cutting calories while adding mileage — intentional or accidental under-fueling drives RED-S
- ·Treating a missed period as proof you're training hard enough — it's often the opposite
- ·Stacking hard weeks back-to-back without recovery
- ·Ignoring bone pain because your pace is improving — stress fractures can build silently
How to fix / recover
- ·Eat enough to fuel runs and daily life — not just on workout days; rest days need full meals
- ·Track period changes when mileage or intensity jumps
- ·Reduce training load and prioritize nutrition before pushing mileage again
- ·See a doctor if your period stops or becomes irregular while training hard — don't wait months to ask
- ·Address iron levels if you're tired despite sleep (common with heavy periods)
- ·Cross-train while bone pain heals — see stress fractures on the main injuries page
- ·A sports dietitian can help if under-fueling is hard to spot on your own
Practical fueling awareness
- ·Most active women need roughly 1,800–2,400+ kcal/day depending on size and training — under-eating by even 300–500 kcal daily adds up over weeks
- ·Pre-run (60–90 min before): banana + peanut butter, toast with jam, or yogurt with granola
- ·Post-run (within 1–2 hours): protein + carbs — chocolate milk, eggs on toast, or a balanced meal with rice/pasta and vegetables
- ·Rest days still need full meals — this is when your body repairs bone and tissue
Estrogen and bone loss
- ·Estrogen helps maintain bone density — when periods stop or become irregular from low energy, bone turnover can outpace rebuilding
- ·Young runners with RED-S can lose bone density that takes years to recover even after eating enough again
- ·This is why a missed period plus bone pain is a red flag, not something to push through
When to see a specialist
- ·Missed periods, stress fracture suspicion, or unexplained fatigue — see your GP or sports medicine doctor
- ·Pinpoint bone pain that worsens with running — imaging may be needed
- ·History of disordered eating or repeated stress injuries — ask about a full RED-S workup
Related: Women's running guide · Stress fractures (all runners)
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