The short answer
RED-S can affect cyclists of any sex. It is not diagnosed by body weight, a calorie target, one hormone or an online energy-availability result.
The 2023 International Olympic Committee consensus defines Relative Energy Deficiency in Sport—now commonly styled REDs—as impaired physiological or psychological functioning associated with exposure to problematic low energy availability. The model includes possible effects across multiple body systems and athletic performance.
The word problematic matters. A short period of lower energy availability does not produce identical harm in every athlete. Duration, magnitude, frequency, sex, age, health, training and other stressors modify the response.
The practical approach is:
- recognise a pattern that deserves attention;
- avoid diagnosing it from a symptom list or calorie calculation;
- assess alternative causes; and
- use a physician-led, multidisciplinary pathway when RED-S is suspected.
RED-S, low energy availability and energy balance are different
These terms are related, not interchangeable.
Energy availability (EA) is a conceptual amount of dietary energy remaining after exercise expenditure, scaled to fat-free mass:
EA = (energy intake − exercise energy expenditure) ÷ fat-free mass
Low energy availability (LEA) describes exposure in which the energy remaining may be insufficient to support all physiological functions. It can arise intentionally, through weight-control behaviour, or unintentionally when training demand rises faster than intake.
RED-S/REDs describes a clinically assessed syndrome of impaired functioning associated with problematic LEA.
Energy balance compares intake with total energy expenditure. It is not the same equation. Body weight can also remain fairly stable while intake, expenditure, glycogen, water and metabolic adaptation move beneath the surface.
That means neither weight stability nor an EA estimate can prove a diagnosis.
Why cyclists can be exposed to low energy availability
Cycling combines several relevant pressures:
- long sessions with high energy expenditure;
- power-to-weight language and visible body-composition comparison;
- training camps and stage events that compress recovery;
- deliberate or accidental under-fuelling on the bike;
- appetite that may not immediately match expenditure;
- limited bone-loading stimulus from the sport itself; and
- busy riders who fit training around work and family but fail to expand meal planning with it.
A review focused on male cyclists found cycling-specific evidence of energy deficits and associations involving bone and endocrine outcomes. It also emphasised how little male-specific research existed.
An observational study of 50 competitive male road cyclists used a sport-specific questionnaire plus clinical interview and compared groups across bone, endocrine and performance measures. That supports closer attention in male riders. It does not prove a prevalence for every cycling population or that LEA caused every difference.
Another study of 108 non-elite male endurance athletes estimated a high proportion at risk and found cyclists had lower calculated EA than runners in that cohort. The authors explicitly noted that their categories came from female cut-points and required validation in men.
Roadman's conclusion is measured: cycling creates plausible exposure and documented concern. It does not make every lean or tired cyclist a RED-S patient.
Are 30 and 45 kcal/kg FFM/day clinical cut-offs?
No. They are widely quoted research reference points.
The familiar story says:
- above 45 is optimal;
- 30–45 is a grey zone; and
- below 30 is a danger zone where systems shut down.
That presentation is too categorical.
The figures developed largely from controlled work in young women and particular physiological outcomes. A review of prospective LEA evidence explains the gap between controlled findings and free-living athletes. Responses differ between systems and individuals, and the evidence base is not equally developed in males.
The IOC consensus moved away from a single universal threshold toward problematic LEA exposure, considering duration, magnitude and frequency plus modifiers.
A 2024 critical review goes further, challenging causal overreach and the tendency to diagnose RED-S from nonspecific symptoms. Its authors argue for a wider health-first assessment that keeps training, sleep, mental health, illness, nutrition and undiagnosed clinical conditions open as possible contributors.
Those perspectives can coexist:
- inadequate energy availability can harm health and performance;
- the 30/45 traffic-light model is not a universal diagnostic instrument; and
- the athlete is better served by a careful differential assessment than a confident label based on weak inputs.
Can an energy availability calculator diagnose RED-S?
No.
The arithmetic is simple. The inputs are not.
Energy intake error
A systematic review of dietary assessment in athletes found that self-reported energy intake underestimated intake by an average of 19% when compared with doubly labelled water across the included comparisons. Individual error can move in either direction.
Exercise expenditure error
Power-meter kilojoules can help estimate the energy cost of cycling, but device accuracy, drivetrain measurement, metabolic efficiency, off-bike exercise and the definition of exercise expenditure still matter. Generic hours-times-intensity equations add another layer of assumption.
Fat-free-mass error
DXA, bioimpedance and circumference methods do not return perfectly interchangeable values. Hydration, device and protocol affect body-composition estimates.
When three uncertain inputs are combined, a result of 29 versus 31 cannot support a red-versus-yellow clinical decision.
The updated Roadman Energy Availability Estimator therefore shows the equation and the limitations. It no longer claims to screen RED-S, call a value optimal or dangerous, or prescribe an immediate calorie change.
Use it to ask better questions:
- Am I logging the same days for intake and exercise?
- Did training rise without a matching fuelling plan?
- Am I repeatedly missing food before, during or after long sessions?
- Are health or performance indicators changing?
Then take the wider pattern to appropriate care.
Signs and symptoms of RED-S in cyclists
The IOC CAT2 groups primary and secondary indicators and weights them by evidence, severity and clinical usefulness. A generic website checklist cannot recreate that process.
Possible indicators include:
- menstrual disturbance, including prolonged amenorrhoea;
- reduced libido or fewer morning erections in males;
- bone stress injury or low bone mineral density;
- low T3 or selected reproductive-hormone changes;
- eating-disorder or disordered-eating risk;
- recurrent illness;
- gastrointestinal disturbance;
- sleep or mood change;
- fatigue; and
- altered training response or performance.
These can appear in different combinations. A rider does not need to be underweight, and an athlete with adequate body mass can still require assessment.
They are also nonspecific. Iron deficiency, thyroid disease, infection, depression, sleep disorders, medication effects, excessive training load, gastrointestinal disease and other conditions can create parts of the same picture.
The safe rule is not “three symptoms equal RED-S.” It is “persistent or clinically important change deserves assessment.”
Female cyclists: menstrual function and bone health
Missing or markedly altered periods are not a badge of serious training. They can have several causes and warrant medical assessment.
Hormonal contraception may also change or mask bleeding patterns, so bleeding alone cannot confirm normal reproductive function or exclude RED-S. Pregnancy, perimenopause, polycystic ovary syndrome, thyroid disease and other causes belong in the differential.
Bone health matters because energy deficiency and menstrual dysfunction can interact with skeletal risk. Bone stress injury is particularly important; it may change training and sport-participation decisions even before every causal question is resolved.
Do not use one return of bleeding, one normal blood value or a pain-free week as automatic clearance. Bone and reproductive recovery can operate on different timescales.
Male cyclists: libido is relevant, testosterone is not the whole diagnosis
RED-S is not a female-only issue.
Male indicators in the CAT2 include reduced sex drive and fewer morning erections. Testosterone may be clinically relevant, but one low result does not identify the cause and one normal result does not clear the whole system.
The dedicated cycling and testosterone guide explains repeat morning testing and alternative causes. The key distinction here is that RED-S assessment brings reproductive information together with bone, metabolic, nutritional, psychological and training context.
Do not convert “male cyclist + fatigue + low-normal testosterone” into a diagnosis. Do ask whether energy intake, weight-control behaviour, bone health, sexual function and training load have changed.
Bone health: cycling adds an important reason to look
Cycling is excellent cardiovascular exercise but supplies less impact loading than running or jumping.
A systematic review of cycling and bone health reported lower bone mineral density at important sites, including the lumbar spine, in adult road cyclists across parts of the literature. Causes are multifactorial and the studies do not show that every cyclist has poor bone health.
Low energy availability can add another skeletal concern. A bone stress injury in a cyclist should therefore prompt a wider review of:
- injury location and history;
- energy availability and eating behaviour;
- menstrual or reproductive function;
- calcium, vitamin D and wider dietary context;
- medicines and medical history;
- bone-loading exercise; and
- whether imaging or DXA is indicated.
That review belongs with sports medicine and appropriate dietetic support. Strength and impact work may form part of later rehabilitation, but it does not replace restoring adequate energy or managing the injury.
Does RED-S always reduce performance?
No. Performance is not a reliable lie detector.
Some athletes maintain or briefly improve performance while health is deteriorating. Lower body mass can also create a short-term climbing benefit that masks a worsening physiological situation. Conversely, poor performance has many causes unrelated to RED-S.
The IOC model includes decreased training response, endurance performance, power, strength and other potential outcomes. It does not require every one.
The 2026 review of short experimental LEA studies found early biochemical changes were not uniform. Leptin fell consistently, while T3 remained stable in most included studies and testosterone decreased in half of interventions. The authors highlighted heterogeneity and the need for standardised, sex-specific work.
That is precisely why a single hormone panel cannot diagnose the condition.
How RED-S is assessed: the IOC CAT2 pathway
The IOC REDs CAT2 review states clearly that there is no single validated diagnostic test. It uses three steps:
1. Initial screening
An appropriately validated questionnaire or clinical interview may identify athletes who need further assessment. A screen finds risk; it does not make the diagnosis.
2. Severity and risk assessment
Qualified practitioners assess primary and secondary indicators and use a green, yellow, orange or red framework. The tool also includes sport-participation guidance and decision modifiers.
This traffic light belongs to the clinical tool. It should not be copied onto a calorie calculator.
3. Physician-led diagnosis and treatment
The physician considers other causes and integrates information from a multidisciplinary team, which may include a sports dietitian, psychologist or psychiatrist, sports physiologist, coach and other specialists.
The final plan is developed with the athlete. It includes health, performance, participation and follow-up decisions.
What tests might be used?
There is no universal “RED-S blood panel.”
Depending on the presentation, a clinician may consider:
- full blood count and iron studies;
- thyroid testing;
- reproductive hormones;
- metabolic or lipid markers;
- vitamin D or other tests when indicated;
- ECG or cardiovascular assessment;
- DXA or other imaging for bone health; and
- evaluation for gastrointestinal, endocrine, infectious or psychological causes.
Each test has its own sampling and interpretation rules. Low ferritin is not RED-S. Low T3 is not RED-S. Low testosterone is not RED-S. Normal results do not necessarily exclude a problem elsewhere.
Use the cyclist blood-testing guide for the symptom-led pathway, and the persistent fatigue guide when the concern extends beyond fuelling.
Recovery and treatment
The first objective is to restore health and adequate energy availability. The route depends on why the mismatch developed and how severe the consequences are.
Possible components include:
- increasing energy intake;
- changing the timing and distribution of food around training;
- reducing or modifying exercise energy expenditure;
- treating an eating disorder or disordered eating;
- addressing bone, reproductive, endocrine, cardiovascular or gastrointestinal problems;
- reducing pressure around weight and body composition;
- psychological support; and
- a staged return to training and performance.
A systematic review of REDs interventions found only 11 eligible studies. Increasing intake, combined intake-and-expenditure change, dietary approaches, education/counselling and a hormonal intervention were represented. The evidence supports nutrition as central but does not justify one universal calorie addition or recovery duration.
Do not prescribe “add 400 calories for six weeks” from an online estimate. The rider may need more or less, training may need to change, an eating disorder may require specialist treatment, and bone or cardiovascular risk may alter participation immediately.
Should a cyclist stop training?
Sometimes training continues with changes. Sometimes removal from sport is appropriate.
The decision depends on severity and risk, not on motivation. Bone stress injury, cardiovascular findings, severe energy deficiency, significant eating-disorder risk and other red or orange indicators can materially change participation advice.
Use the clinical CAT2 framework. Do not self-assign green because power is stable or red because an app showed 29.
When training is allowed, the plan may begin by reducing energy cost, removing unnecessary intensity, protecting recovery and gradually restoring strength and impact loading where appropriate. A commentary on musculoskeletal return to performance discusses supervised progressive resistance and impact training after energy needs are met.
This is relevant to Roadman's strength-and-conditioning work: strength can support the return. It cannot compensate for unresolved energy deficiency or clear an athlete to train.
Race weight without the false precision
Power-to-weight matters on climbs. Health determines whether useful power can be trained and sustained.
Avoid fixed rules such as:
- a universally safe 300-calorie deficit;
- a minimum percentage of body fat for every male or female rider;
- a 4–12-week maximum diet phase;
- “deficit only on rest days” as a guarantee; or
- a calculator value that authorises further weight loss.
Body-composition work is not appropriate for every rider or every phase. Previous RED-S, bone injury, menstrual or sexual-function change, persistent fatigue, an eating disorder, distress around food or a very lean starting point all strengthen the case for qualified support and may make weight loss inappropriate.
The lighter-faster myth guide keeps the performance question tied to health and sustainable power.
When to seek help
Arrange qualified assessment when you notice persistent or important changes such as:
- missed or markedly altered periods;
- reduced libido, fewer morning erections or sexual dysfunction;
- a bone stress injury or repeated bone injury;
- recurrent illness;
- persistent fatigue, low mood or impaired daily function;
- rapid or unexplained weight change;
- a marked decline in training response or performance;
- gastrointestinal symptoms that interfere with intake;
- rigid food rules, compensatory exercise, bingeing, purging or distress around eating; or
- concern from a partner, coach or clinician about health or eating behaviour.
Seek urgent care for fainting, chest pain, significant breathlessness, confusion, severe weakness, signs of medical instability, acute mental-health risk or an eating-disorder crisis. A cycling website and app are not appropriate triage tools for those situations.
What the Roadman app can—and cannot—do
The upcoming Roadman app focuses on strength, conditioning and recovery. It can help riders and coaches see context that is otherwise scattered:
- training load and session type;
- recovery and symptom trends;
- strength and bone-loading work;
- fuelling notes without labelling food good or bad;
- menstrual or sexual-health context when the rider chooses to record it; and
- a concise history for a qualified appointment.
It will not calculate a RED-S diagnosis, assign an IOC traffic light, prescribe energy intake, treat an eating disorder or clear a rider for sport.
Join the single Roadman app waiting list if you want training and recovery context designed with those boundaries. The source tells us which problem matters to you; everyone joins the same audience.
Bottom line
Problematic under-fuelling can harm cycling health and performance. Calculator certainty can harm too.
Keep the useful idea: training leaves an energy cost that must be supported. Lose the false rule that 29 diagnoses RED-S and 46 proves optimal health. Look for the whole pattern, protect bone and reproductive health, keep alternative causes open and use the physician-led CAT2 pathway when concern is real.