Abstract
BACKGROUND: Nordic skiing, an energy-demanding endurance sport, may be particularly susceptible to low energy availability (LEA) and relative energy deficiency in sport (REDs). The objective was to examine the nutritional practices and physical symptoms associated with (REDs among young elite Norwegian Nordic skiers during the off-season, with particular emphasis on energy and CHO intake, in the transition from the competitive season to preparation for the subsequent season. METHODS: Thirty female and thirty male Nordic skiers participated in a 24-week controlled clinical trial. The daily dietary intake variables were carbohydrates (CHO), protein, and calcium (Ca) intake and weekly training hours. The blood variables were vitamin D, total osteocalcin (tOC), procollagen type 1 N-terminal propeptide/cross-linked C-telopeptide type 1-collagen (PINP1/CTX1) ratio, heart rate (HR), resting metabolic rate (RMR), bone mineral density (BMD), lean body mass (LM), visceral adipose tissue (VAT), and body fat percentage (BF%). RESULTS: Energy intake increased by 25%, and CHO increased by 14.5% for both sexes during the study, and training volume increased by 41% for female athletes and 83% for male athletes, respectively. There were positive correlations between higher BMD, bone markers, RMR, and LM and negative correlations between VAT and REDs symptoms. VAT was correlated with RMR and bone markers. LM emerged as a key predictor for health variables, explaining variability across multiple REDs markers. CONCLUSIONS: Nordic skiers seem unable to increase energy intake sufficiently during the preparation period, leading up to the competitive season, as demonstrated by a large discrepancy between changes in energy intake, especially CHO, and exercise volume. The correlations between energy intake and BMD, RMR, VAT, and HR underscore the clinical consequences of insufficient energy intake, which may arise if individuals focus on low body mass and body fat percentage without sufficient knowledge. VAT, tOC, and the P1NP/CTX-ratio are promising indicators for monitoring dietary interventions in individuals with REDs and should be considered in future research on REDs treatment strategies.