The most consequential nutritional problem in adolescent female sport is not a deficiency of any particular nutrient. It is insufficient total energy relative to training load, and it is frequently accidental.
What low energy availability means
Energy availability is the energy remaining for physiological function after the energy cost of exercise is subtracted from intake.
When it falls below the level required to sustain normal function, the body downregulates. The systems affected include reproductive function, bone metabolism, immune function, protein synthesis and metabolic rate.
The syndrome has been described under several names, most recently in frameworks describing relative energy deficiency in sport. The specific terminology matters less than the recognition that the consequences extend well beyond athletic performance.
Why it happens without an eating disorder
This is the point most frequently missed. Low energy availability can arise entirely without disordered eating.
An adolescent whose training load increases substantially — new season, new squad, additional sessions — without a corresponding increase in intake will be in deficit, and appetite does not reliably increase in proportion to exercise, particularly in the hours immediately after intense training.
Schedules contribute. Training before school or immediately after, with limited eating opportunities, produces a real logistical barrier.
General nutritional advice contributes as well. Public health messaging is oriented towards reducing intake, which is appropriate for the general population and actively wrong for a growing adolescent training twelve hours a week.
Disordered eating is a significant cause and is more common in some sports than others. But treating every case as psychological misses the substantial number that are logistical.
The bone consequence
This is why the issue matters beyond the immediate.
Adolescence is the critical window for bone mineral accrual. A large proportion of adult peak bone mass is laid down during the adolescent years, and peak bone mass is a major determinant of fracture risk decades later.
Low energy availability during this period impairs accrual. The evidence indicates that bone density lost or not gained during adolescence is not fully recoverable later, even after energy availability is restored.
In practical terms: a sixteen-year-old in energy deficit is making a decision with consequences at sixty, and neither she nor anyone around her is likely to be framing it that way.
The intermediate consequences are also real. Stress fractures are markedly more common in athletes with low energy availability, and they are among the more common causes of extended absence from sport in adolescents.
Amenorrhoea is a clinical sign
Absent or irregular menstruation in an athlete is frequently regarded — by athletes, coaches and sometimes clinicians — as a normal consequence of training, and occasionally as convenient.
It is a sign of endocrine disruption and should prompt assessment. Reproductive function is among the first systems downregulated in energy deficit, which makes it an early and useful indicator.
The prevalence of menstrual dysfunction in adolescent athletes is substantially higher than in non-athletes, particularly in endurance and aesthetic sports, and a large proportion goes unreported because nobody asks.
Iron, separately
Iron deficiency is distinct from energy availability and common in adolescent female athletes for several converging reasons: menstrual losses, increased requirements during growth, exercise-related losses, and in some cases reduced intake of iron-rich foods.
The performance effects of iron deficiency, including before anaemia develops, are reasonably well documented for endurance capacity.
Ferritin rather than haemoglobin is the appropriate measure, since stores deplete first. Testing is cheap and is frequently not done.
Supplementation should follow testing rather than precede it — iron overload is harmful and self-supplementation without measurement is not advisable.
What good practice looks like
Fuel around training rather than only at meals. The window immediately after intense exercise matters, and it frequently coincides with travel home and appetite suppression, which is a logistical problem with a logistical solution.
Increase intake when load increases. This sounds obvious and is routinely not done, because the load change is planned and the intake change is not.
Treat menstrual changes as information rather than as a side effect.
Test iron status where symptoms or heavy bleeding are present.
Be alert to sports where the risk is elevated — endurance, weight-category and aesthetic sports have consistently higher prevalence in the research.
The coaching language problem
A final point that recurs in qualitative research with athletes.
Comments about weight and body composition from coaches are reported frequently and are associated with disordered eating in follow-up studies. This holds even for comments intended as performance advice.
Professional guidance in most sports now discourages weight discussion with adolescent athletes outside a clinical context, and this is one of the clearer cases where the guidance has good reason behind it and is widely ignored.
The performance question a coach can usefully ask is whether the athlete is eating enough to support what she is being asked to do. That is almost always the more relevant variable, and it points in the opposite direction from the conversation that usually occurs.