Relative Energy Deficiency in Sport (RED-S) happens when your body doesn't get enough fuel to support everything it needs to do: both exercise and basic health functions.
This is about chronic under-fueling over an extended period, not one missed meal or a single off week. And importantly, you don't have to "look underweight" for RED-S to be present.
Who RED-S can affect
RED-S isn't limited to elite or competitive athletes. It can affect:
- Recreational athletes: runners, cyclists, CrossFit athletes, swimmers, and more.
- Teens and college athletes.
- Postpartum parents getting back into exercise.
- Anyone training or exercising regularly while eating too little.
How under-fueling affects your body
When energy intake is too low, your body goes into conservation mode, and healing and performance are no longer the priority. RED-S can impact:
- Injury recovery: slower healing and lingering pain.
- Muscle strength and endurance.
- Bone health: increased risk for stress fractures.
- Hormone levels: missed periods, low testosterone.
- Energy and mood.
- Immune function: getting sick more often.
Common signs of under-fueling
Common signs include persistent fatigue despite training less, frequent injuries or flare-ups, slow progress in rehab, feeling cold often, poor sleep or low mood, and missed or irregular menstrual cycles. If this sounds familiar, it doesn't mean you've done anything wrong. Many people simply don't realize they're under-fueling.
Why physical therapists talk about RED-S
We see how fueling affects the healing process. You can do all the right things in training and rehab, but if your body doesn't have enough energy, progress may stall. We don't prescribe diets, but we do care about the basics: eating enough overall, getting adequate protein, and supporting your body during recovery. Sometimes the best next step is involving a registered dietitian, who can give individualized guidance.
Recovering slowly or dealing with recurring injuries? Kauno's physical therapists look at the whole picture, including fueling, and connect you with a dietitian when it helps.
book a sessionthe takeaway
If you're active, injured, or returning to exercise, food is part of rehab. More training doesn't always mean better results, and recovery requires fuel.
Frequently asked questions
What is RED-S?
Relative Energy Deficiency in Sport (RED-S) is when your body doesn't get enough fuel to support both exercise and basic health functions. It stems from chronic under-fueling over time, not a single missed meal.
Do I have to be underweight to have RED-S?
No. You don't have to "look underweight" for RED-S to be present. It comes from under-fueling relative to your needs, which can happen at many body sizes.
What are the common signs?
Persistent fatigue despite training less, frequent injuries or flare-ups, slow rehab progress, feeling cold often, poor sleep or low mood, and missed or irregular menstrual cycles.
Can a physical therapist help with RED-S?
PTs don't prescribe diets, but we care about the basics (eating enough, adequate protein, and supporting recovery) and can refer you to a registered dietitian for individualized guidance.
