Under-eating & RED-S: Under-eating and RED-S: what happens when you train on too little food.
6 sections, about 11 minutes in total
2023
The IOC updated its RED-S guidance in 2023. It applies to everyday exercisers, not only elite athletes.
Months
Eating too little for a few months is enough to stop your period and start weakening bone.
3 months
Three months without a period is the point to find out why. Do not wait longer.
Start with the signs
The signs of under-fuelling.
Under-fuelling means eating less than your training and your body need. The signs are easy to miss because they can look like being fit or being busy. Tap the signs you have to see why they happen.
Nothing you tap is stored. This is a mirror for you, not a form for us.
What the evidence says
What the evidence says about RED-S.
A missing period in a woman who trains hard is a warning sign, not a sign of fitness. Under-fuelling eventually hurts performance too. The way back is more food and real rest.
These summaries reflect the cited research and will change if the research changes.
A quick self-check
Check your own energy balance.
Five questions about how you eat, train and recover. Answer them and the radar shows where your energy balance is weakest.
1/5How do you eat around training?
2/5How many real rest days do you take each week?
3/5How has your cycle been lately?
4/5How do you feel outside training?
5/5How does your training volume compare with a year ago?
Your profile
0/5 answered
This is a self-check for learning, not a test or a diagnosis.
The energy budget
How the energy budget works.
Energy availability is the energy your body has left after training. When it drops too low, your body starts cutting back. Click through the four steps.
Tap a step to open it. Each one carries the detail.
Why more discipline does not fix this
Low energy availability is not a sign of weak discipline. It means your body does not have enough energy left after training, and hormones are the first thing it cuts back. The 2023 IOC consensus states directly that performance eventually falls too, so under-fuelling is not a shortcut.
The key warning sign
What a missing period means when you train hard.
A missing period is the clearest sign your body is short on energy. It is not a sign of fitness. Here is what it does and does not tell you.
What it means
- It is the clearest early warning sign of an energy deficit, because reproduction is the first system the body suspends
- Low estrogen follows, and bone renewal slows within months, mostly without symptoms
- It gives early information about fuel, stress and training load, often before blood tests change
What it doesn't mean
- That you're “finally lean enough” or training at the right intensity
- That it's a normal, harmless side effect for women who train. It isn't
- That it can wait. Three or more months without a period needs checking, to rule out other causes and check on bone
Other things can stop a period too, such as pregnancy, PCOS, a thyroid problem or high prolactin. Rule those out first. If the cause is too little energy, the habits below are the way back.
The habits that help
How to rebuild your energy.
Eat more, especially around training, and rest properly. Fuelling around training does the most because that is where the gap is largest. Your period can take months to return even when you are doing it right. Tap a habit to see what to do.
Tap a tab to open it. The detail lands here.
If eating more feels frightening rather than just hard, that deserves specialised support from a dietitian or therapist, and we gladly refer you, because asking for that help is the opposite of failure.