Can a contemporary dietary assessment tool or wearable technology accurately assess the energy intake of professional young rugby league players? A doubly labelled water validation study.

Accurate quantification of energy intake is imperative in athletes; however traditional dietary assessment tools are frequently inaccurate. Therefore, this study investigated the validity of a contemporary dietary assessment tool or wearable technology to determine the total energy intake (TEI) of professional young athletes. The TEI of eight professional young male rugby league players was determined by three methods; Snap-N-Send, SenseWear Armbands (SWA) combined with metabolic power and doubly labelled water (DLW; intake-balance method; criterion) across a combined ten-day pre-season and seven-day in-season period. Changes in fasted body mass were recorded, alongside changes in body composition via isotopic dilution and a validated energy density equation. Energy intake was calculated via the intake-balance method. Snap-N-Send non-significantly over-reported pre-season and in-season energy intake by 0.21 (2.37) MJday ( = 0.833) and 0.51 (1.73) MJday ( = 0.464), respectively. This represented a and standardised mean bias, and and typical error. SenseWear Armbands and metabolic power significantly under-reported pre-season and in-season TEI by 3.51 (2.42) MJday ( = 0.017) and 2.18 (1.85) MJday ( = 0.021), respectively. This represents a and standardised mean bias, and and typical error. There was a larger daily error reported by SWA and metabolic power than Snap-N-Send across pre-season (3.30 (2.45) MJday; ES = 1.26 ± 0.68; = 0.014) and in-season periods (1.67 (2.00) MJday; ES = 1.27 ± 0.70; = 0.012). This study demonstrates the enhanced validity of Snap-N-Send for assessing athlete TEI over combined wearable technology, although caution is required when determining the individual TEIs of athletes via Snap-N-Send.