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Cycling has a long and unhealthy fascination with being lighter. Power-to-weight is a real physical quantity, climbing really is easier at lower mass, and the sport has spent decades turning that arithmetic into a culture. What the arithmetic leaves out is what happens when the energy coming in stops covering the energy going out — not for a week, but as a way of life.
That state has a name. Low energy availability is the underlying problem; REDs — Relative Energy Deficiency in Sport — is the syndrome of health and performance consequences that follows. The International Olympic Committee published an updated consensus statement on it in 2023, drawing on more than 170 research publications since the previous one, and the short version is that this is more common, more consequential and less visible than the sport has tended to assume.
What low energy availability actually means
It is not the same as not eating enough in ordinary terms, and it is not the same as being underweight. The quantity that matters is what remains for the rest of your body after training has taken its share.
Consider a rider who eats a perfectly reasonable amount of food, and then rides for five hours. Everything the ride consumed comes off the top. What is left has to run the immune system, bone remodelling, hormone production, digestion, brain function and repair. If that remainder is too small for too long, the body does what any system under an energy shortfall does: it economises, shutting down the functions it can survive without in the short term.
Which is why a rider can be eating what looks like plenty, be at what looks like a healthy weight, and still be deeply energy-deficient. Bodyweight is a poor detector of this, and the sport's habit of using it as one is part of the problem.
Schematic. The point is the remainder, not the intake — which is exactly why "but I eat loads" is not reassurance, and why adding training hours without adding food is the most common way in.
What it does
The consensus statement describes effects across a wide range of body systems — bone health, immune function, endocrine function, metabolic rate, cardiovascular and haematological measures, mental health, growth and development, and gastrointestinal function — alongside performance consequences. It also frames low energy availability as a spectrum, ranging from adaptable, short-term states to genuinely problematic ones, rather than a switch that flips.
For a rider, the everyday face of it looks like this:
Training loads that used to produce progress produce nothing, or a slow decline. The rider's instinct is to train harder, which makes it worse.
Sessions that were routine last season leave you flat for two days. Sleep is often disturbed rather than deep.
Repeated colds, cuts and saddle sores that take weeks, niggles that do not resolve.
In cycling these are less common than in running, which is a double-edged mercy: the warning sign that shows up first in other sports may simply never appear.
Metabolic rate falls to conserve energy. Riders describe being cold in rooms where nobody else is.
Flattened mood, loss of drive to ride, reduced libido. These are physiological consequences, not character flaws.
This is a medical problem, not a training one
If several of the signs above describe you — and particularly if your menstrual cycle has changed or stopped, or you have had a bone stress injury — the next step is a doctor or a registered sports dietitian, not a new training plan. Assessment tools exist for exactly this and they belong in trained hands. Nothing on this page is a diagnosis, and self-managing an energy deficit by adjusting your own diet further is the failure mode, not the fix.
Who it happens to
Female riders
Disturbance or loss of the menstrual cycle is one of the clearest indicators, and it is not a normal consequence of training. It warrants medical attention rather than acceptance.
Male riders
Long assumed to be unaffected, and it is not true. The 2023 consensus statement explicitly addresses accumulating evidence of low energy availability in males, where the signs are less obvious and therefore missed for longer.
Riders chasing a number
Anyone whose training is organised around a target weight or a power-to-weight figure is in the highest-risk group, regardless of sex or level.
High-volume amateurs
You do not need to be an elite to get here. A full-time job plus fifteen hours a week plus an unchanged diet is a very ordinary route into a deficit.
The performance argument, for anyone unmoved by the health one
Some riders will read the health consequences and quietly conclude that a bit of deficit is a price worth paying for climbing faster. It is worth being direct with that reasoning on its own terms: it does not work.
An energy-deficient rider adapts poorly to training, recovers slowly, gets ill more often and loses training weeks to it. Lean muscle goes along with anything else. The power number falls faster than the weight does, and the ratio that the whole exercise was supposed to improve gets worse. There is a reason race weight without losing power spends most of its length on how not to do this.
Preventing it, in practical terms
- When training goes up, food goes up. The most common route into a deficit is not a diet at all — it is adding hours in spring and eating the same as in February.
- Fuel the ride itself. Carbohydrate during long rides reduces the size of the hole you finish with, which is the whole game. Fuelling long rides: carbs per hour is the practical version.
- Eat close to the session. Spreading intake across the day, and especially around training, matters — the deficit is dynamic, not just a daily total.
- Treat rest days as refuelling days. Eating less on days off, because you "did nothing", is how riders arrive at Monday's session already behind. Recovery is training makes the wider case.
- Be suspicious of any plan built around a weight target. Especially one with a date attached to it.
Where the data can help — and where it cannot
Training software can tell you that your fitness is drifting down, that your heart rate has climbed for the same power, that your form has been negative for two months. Those are useful facts and Moveee will show them to you: your fitness and fatigue trend is exactly the kind of slow decline that is obvious on a chart and invisible day to day, and fitness, fatigue and form explained covers how to read it.
What no app can tell you is whether you are eating enough for your body to function. That takes a person, some blood work, and an honest conversation. If the last few paragraphs have felt uncomfortably familiar, that conversation is the most valuable thing you could do for your riding this season — and it is considerably more likely to make you faster than another training block would.
Sources 2
Where this article summarises a study, the study itself is linked — not a write-up of it.
- 1 Mountjoy M, Ackerman KE, Bailey DM, et al. 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs) · British Journal of Sports Medicine · 2023
- 2 Pengelly M, Pumpa K, Pyne DB, Etxebarria N. Iron deficiency, supplementation, and sports performance in female athletes: A systematic review · Journal of Sport and Health Science · 2024
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