Within‐day energy deficiency and reproductive function in female endurance athletes

<jats:p>We aimed to estimate and compare within‐day energy balance (WDEB) in athletes with eumenorrhea and menstrual dysfunction (MD) with similar 24‐hour energy availability/energy balance (EA/EB). Furthermore, to investigate whether within‐day energy deficiency is associated with resting metabolic rate (RMR), body composition, S‐cortisol, estradiol, T<jats:sub>3</jats:sub>, and fasting blood glucose. We reanalyzed 7‐day dietary intake and energy expenditure data in 25 elite endurance athletes with eumenorrhea (n = 10) and MD (n = 15) from a group of 45 subjects where those with disordered eating behaviors (n = 11), MD not related to low EA (n = 5), and low dietary record validity (n = 4) had been excluded. Besides gynecological examination and disordered eating evaluation, the protocol included RMR measurement; assessment of body composition by dual‐energy X‐ray absorptiometry, blood plasma analysis, and calculation of WDEB in 1‐hour intervals. Subjects with MD spent more hours in a catabolic state compared to eumenorrheic athletes; WDEB < 0 kcal: 23.0 hour (20.8‐23.4) vs 21.1 hour (4.7‐22.3), <jats:italic>P </jats:italic>= .048; WDEB < −300 kcal: 21.8 hour (17.8‐22.4) vs 17.6 hour (3.9‐20.9), <jats:italic>P </jats:italic>= .043, although similar 24‐hour EA: 35.6 (11.6) vs 41.3 (12.7) kcal/kg FFM/d, (<jats:italic>P </jats:italic>= .269), and EB: −659 (551) vs −313 (596) kcal/d, (<jats:italic>P </jats:italic>= .160). Hours with WDEB <0 kcal and <−300 kcal were inversely associated with RMR<jats:sub>ratio</jats:sub> (<jats:italic>r</jats:italic> = −.487, <jats:italic>P </jats:italic>= .013, <jats:italic>r</jats:italic> = −.472, <jats:italic>P </jats:italic>= .018), and estradiol (<jats:italic>r</jats:italic> = −.433, <jats:italic>P </jats:italic>= .034, <jats:italic>r</jats:italic> = −.516, <jats:italic>P </jats:italic>=<jats:italic> </jats:italic>.009), and positively associated with cortisol (<jats:italic>r</jats:italic> = .442, <jats:italic>P </jats:italic>= .027, <jats:italic>r</jats:italic> = .463, <jats:italic>P </jats:italic>= .019). In conclusion, although similar 24‐hour EA/EB, the reanalysis revealed that MD athletes spent more time in a catabolic state compared to eumenorrheic athletes. Within‐day energy deficiency was associated with clinical markers of metabolic disturbances.</jats:p>