Not Eating Enough
It is the most common mistake in serious amateur training and the least likely to be diagnosed, partly because it looks like discipline.
Last updated: 30 September 2026
Overview
Most training mistakes announce themselves. This one looks like discipline, gets praised, and is often the reason someone has not progressed in a year.
There is a clinical framework for the serious end of it, and this article reports what that framework says. It does not diagnose anything, and the point at which this stops being a training article and becomes a medical one is marked below.
Quick Answer
Low energy availability means not eating enough to cover both training and normal bodily function. The 2023 IOC consensus statement describes the resulting syndrome, Relative Energy Deficiency in Sport, as affecting health and performance in both female and male athletes.
Key Points
- Underfuelling stalls progress before it causes symptoms you notice.
- It affects men as well as women. The male evidence has grown substantially.
- Low carbohydrate availability is part of it, not just low calories.
- Warning signs include lost periods, poor sleep, illness and stalled lifts.
- Persistent symptoms are a GP conversation, not a wiki one.
What it is
Low energy availability is eating too little relative to what you expend in training — so what is left does not cover the ordinary business of being alive.
The body responds by economising. Reproductive hormones drop, bone turnover shifts, immune function falls, thyroid output reduces, and non-exercise movement quietly declines. None of that presents as a diagnosis. It presents as being tired, ill, plateaued and flat.
The IOC introduced the term Relative Energy Deficiency in Sport in 2014 to name the syndrome of health and performance outcomes that follow, in female and male athletes. The 2023 statement notes more than 170 original research publications since 2018, including a growing role for low carbohydrate availability specifically, further evidence of the interplay between mental health and REDs, and considerably more data on the effects in males.
That last point matters, because this is still widely believed to be a women's issue and it is not.
Who this happens to
Rarely someone being careless. Usually someone being conscientious:
| Situation | How it happens |
|---|---|
| A long diet that never ended | Three months became fourteen |
| Training load went up, intake did not | Added running to lifting, ate the same |
| Hybrid or endurance training | Two sports, one sport's intake |
| "Clean eating" | High volume, low calorie density, unintentionally low intake |
| Weight-class or aesthetic sport | Institutional pressure to stay light |
| A teenager cutting | See teenagers and cutting |
The signs
Individually these have other explanations. Together, and alongside a hard training load and a low intake, they form a pattern worth taking seriously.
Performance
- -Lifts flat or going backwards for months despite good programming
- -Every session feels heavy from the warm up
- -Recovery between sessions taking days longer than it used to
Body
- -Periods becoming irregular or stopping
- -Reduced libido, in either sex
- -Feeling cold constantly
- -Frequent colds and infections that linger
- -Hair thinning, nails breaking, skin changes
- -Stress fractures or bone injuries from ordinary loads
Mind
- -Poor sleep despite exhaustion
- -Low mood, irritability, anxiety
- -Preoccupation with food
- -Difficulty concentrating
The two that most warrant attention are a lost or irregular menstrual cycle and a bone injury from ordinary training. Neither is something to note and carry on with.
Why it stalls progress
Training is a request; food is the answer. The request is worthless without it.
| What you need it for | What happens without |
|---|---|
| Repairing trained tissue | No adaptation, no growth |
| Fuelling the session | Fewer reps, less stimulus |
| Hormonal function | Poorer recovery and drive |
| Immune function | More sessions missed to illness |
| Bone remodelling | Injury risk rises |
This is why "eat more" is a legitimate answer to a plateau, and why it feels so wrong to someone who has spent two years learning that less is better.
What to do
If this describes you and the symptoms are mild — flat training, always hungry, always cold, nothing more:
1. Work out what you are actually eating. Track honestly for a week, weekends included.
2. Work out what you actually need. Calorie targets, including the training you have added since you last calculated it.
3. Add food gradually. 200 to 300 calories, mostly carbohydrate, held for two weeks.
4. Eat at maintenance for a while. A month or two. Not a bulk, just enough.
5. Expect the scale to rise. Glycogen and water. It is not a failure.
6. Watch the lifts. If they start moving again, that was your answer.
When this stops being a training question
Speak to a GP, and ask about a referral to a registered dietitian, if:
- -Your periods have become irregular or stopped
- -You have had a stress fracture or an unexplained bone injury
- -The symptoms are persistent, or several are present together
- -Eating more feels frightening or impossible
- -Food or your body occupies a large part of your thinking
That last pair is the important one. If adding food is not a practical problem but an emotional one, the useful next step is a conversation with your GP rather than a calorie target. Disordered eating is common in people who train seriously, it is treatable, and nothing on a fitness wiki is a substitute for that conversation.
Common Mistakes
| Mistake | Why it causes problems | Better approach |
|---|---|---|
| Cutting further when progress stalls | Compounds the cause | Eat at maintenance |
| Adding training without adding food | Availability falls twice over | Recalculate when the load changes |
| Treating lost periods as convenient | A signal that should be investigated | See a GP |
| Assuming this only affects women | Male evidence has grown substantially | Same signs, same action |
| Dieting without end | Months become years | Plan the finish |
| Judging intake on memory | Reporting drifts badly | Track for a week |
Frequently Asked Questions
How do I know if I am not eating enough?
Look for the pattern rather than a single symptom: stalled training, constant cold, poor sleep, frequent illness, low libido, irregular or absent periods, alongside a hard training load.
Can men have low energy availability?
Yes. The IOC consensus statement covers female and male athletes, and the 2023 update notes substantially more data on the effects in males.
Will eating more make me fat?
Eating at maintenance will not. You will gain some water and glycogen within days, which is not fat.
Why have my lifts stopped going up?
It is worth checking intake before programming. Underfuelling stalls progress reliably, and no amount of good programming compensates for it.
When should I see a doctor?
If your periods have become irregular or stopped, if you have had a stress fracture, if several symptoms are present together, or if eating more feels frightening rather than simply inconvenient.
Sources
Mountjoy et al. (2023), 2023 International Olympic Committee's consensus statement on Relative Energy Deficiency in Sport (REDs), BJSM - https://pubmed.ncbi.nlm.nih.gov/37752011/
British Dietetic Association - https://www.bda.uk.com/
NHS healthy weight guidance - https://www.nhs.uk/live-well/healthy-weight/