Low energy availability (LEA) is associated with impaired physiological and psychological function in
athletes. Suppressed resting metabolic rate (RMR) has been proposed as a physiological indicator of
LEA (1) . Gastrointestinal symptoms (GIS) are potentially a manifestation of chronic LEA; however, the
relationship between RMR and GIS in athletes remains poorly understood. This study investigated
associations between RMR and GIS at rest and in response to exercise. Forty-six female athletes
(18-39 years) from team, athletic, and endurance sports (e.g., marathon running) completed RMR
assessment following 24h abstinence from strenuous exercise, alcohol, and caffeine, overnight fast,
and 30 min rest, before 30 min measurement in a dark quiet room. The ratio of measured to predicted
RMR (RMRp), calculated using the Cunningham equation, was used to classify athletes as having
normal (≥90%) or suppressed (<90%) RMR (1) . GIS incidence and severity at rest and in response to
exercise was assessed using a modified athlete-specific visual analogue scale (mVAS) (2) .
Constipation was included as a recognised GIS in the Rome IV criteria (3) . Spearman's rank-order
correlations and Mann–Whitney U tests, examined correlations and group differences, respectively.
Correlation strength was interpreted as very weak (<0.200), weak (0.200–0.399), moderate
(0.400–0.599), and strong (≥0.600) with statistical significance accepted at p < 0.05. Mean RMR was
1462 kCal/day (95% CI 1391-1532; with n= 29 normal and n= 17 suppressed categorisation). Total-
GIS incidence was 54% at rest and 72% during exercise, with mean severity scores of 12 (range: 0-
62) and 10 (0-38), respectively. Moderate to weak negative correlations were observed between
measured RMR for GIS incidence, including gut discomfort, total-GIS, and lower-GIS, lower
abdominal bloating, and constipation (r s = -0.296 to -0.446, p≤ 0.030). Similarly, moderate to weak
negative correlations were observed between measured RMR and resting GIS severity, including gut
discomfort, total-GIS, lower-GIS, and constipation (r s = -0.383 to -0.442, p≤ 0.009). When expressed
relative to predicted values (RMR:RMRp), similar weak negative correlations were observed for both
GIS incidence (r s = -0.292 to -0.362, p≤ 0.032) and severity (r s = -0.308 to -0.395, p≤ 0.038). Athletes
with suppressed RMR reported significantly greater resting gut discomfort, total-GIS, lower-GIS, and
constipation (z= -2.075 to -2.444, p≤ 0.038). No significant correlations were identified between RMR
measures and exercise-induced GIS, and no differences were observed between groups in response to exercise. Lower RMR, a proposed indicator of LEA, was associated with greater GIS burden at
rest, but not in response to exercise, suggesting different GIS aetiology and/or pathophysiology.
Consistent findings for both absolute RMR and RMR:RMRp suggest GIS at rest may represent a clinically relevant feature of LEA and could complement existing REDs screening approaches. Further research is required to determine the utility of GIS assessment in identifying athletes at risk of REDs.