REF-343 · Heikura et al., 2018 · International Journal of Sport Nutrition and Exercise Metabolism · Paper
Low energy availability is difficult to assess but outcomes have large impact on bone injury rates in elite distance athletes
Participants
n=59 national/world-class female and male distance athletes: 35 women (13 amenorrheic, 22 eumenorrheic) and 24 men (10 with testosterone in the lowest quartile of the reference range, 14 normal). Group sizes are the abstract's; the total is their sum.
Protocol
EA calculated from 7-day food and training diaries and classified above or below 30 kcal/kg FFM/day
Athletes grouped by reproductive function (amenorrheic vs eumenorrheic; low vs normal testosterone)
Risk categorised with the Female Athlete Triad, LEAF-Q and RED-S tools; metabolic/reproductive hormones, bone mineral density, injury and illness recorded
Key Results
37% of the women were amenorrheic and 40% of the men had low testosterone (15.1 ± 3.0 nmol/L in the low group)
Sex hormones (p < .001), triiodothyronine (p < .05) and bone mineral density (women, p < .05) were significantly lower in the amenorrheic and low-testosterone athletes
Bone injuries were ~4.5-fold more prevalent in the amenorrheic (effect size 0.85, large) and low-testosterone (effect size 0.52, moderate) groups than in the others
Triad and RED-S higher-risk categories had lower T3 and more all-time fractures (male Triad p < .001; male RED-S and female Triad p < .01), and a non-significant but marked (up to 10-fold) higher number of training days lost to bone injury in the preceding year
Authors' conclusion: current reproductive function (questionnaire plus blood hormones) is a more objective and accurate marker of adequate energy than the error-prone, time-consuming dietary and training estimation of EA
Practical Application
In 59 national/world-class distance athletes, those with a suppressed reproductive axis — 37% of the women amenorrheic, 40% of the men low-testosterone — had ~4.5× the bone-injury prevalence, lower T3 and (women) lower bone density; diary-based EA itself was a poorer marker than these reproductive signs. A bone stress injury in an endurance athlete is a reason to check menstrual function or testosterone before blaming training load alone.
Reproductive function is the practical screen: missed cycles in women, low testosterone or its symptoms in men — not a food-diary EA calculation, which the authors found unreliable.
Inference, not tested: the association is cross-sectional; it shows who carries the injuries, not that restoring EA reverses them.
Limitations
Cross-sectional; no intervention, no causal claim
EA from 7-day self-report diaries is noisy — the paper's own conclusion
Elite distance runners and walkers; generalization to other sports not tested
Small subgroups (10-22 per group)
How this entry was checked and changed
Why this level
regraded 2026-09-27 from A: cross-sectional analysis, n=59
Content correction 2026-09-27
"n=37 ... observed over 9 months", "prospective" -> the abstract is a cross-sectional analysis of 13+22 women and 10+14 men (n=59); no 9-month follow-up is described.
"LEA prevalence ~37-80%" -> 37% is the share of amenorrheic women and 40% the share of low-testosterone men; no LEA prevalence range is given.
"4.5× bone injury in persistent LEA vs adequately fuelled" -> the 4.5-fold contrast is amenorrheic / low-testosterone vs other athletes, grouped by reproductive function, not by EA.
"Ferritin lower (p<0.01)", "menstrual dysfunction 2-3× more frequent" -> not in the abstract; removed. Level A -> B (cross-sectional).