## 2 Materials and Methods  
Study Design. This is a descriptive, cross-sectional, and non-experimental study of anthropometric characteristics, estimation of expenditure and energy intake, and nutrient intake estimation in professional male soccer players under 19 years of age, from the first division of youth Spanish football, which corresponds to the highest category for this age group. Participants. Participants belonged to two teams from the same Spanish club, both in the youth category. A total of 41 players participated in this study, consisting of 17 players from the morning training team (mean age: 17.65 \(\pm\) 0.61 years) and 24 players from the evening training team (mean age: 16.87 \(\pm\) 0.45 years). Inclusion criteria for the study were as follows: (a) being a healthy individual with medical authorization for federated sports practice; (b) belonging to one of the two teams in the youth category of the Spanish league; (c) being federated in football; (d) training at different times, either in the morning (8:00-10:30 a.m.) or in the evening (20:00-21:30 p.m.); (e) measurements taken in March, during the competitive phase. Exclusion criteria for the study were: (a) not being of the corresponding age for the youth category, 16-18 years old. All players were previously informed of the objectives and methods of the research, signing the informed consent document before starting the study. For underage players, legal guardians were informed, and they authorized the minor's participation through the corresponding informed consent. Procedure. Evaluations were conducted during each team's training schedule. On the day of evaluation, it was necessary for players not to have performed high-intensity exercises, training, or stretching on the same day. Therefore, anthropometric measurements were taken before training. All players were familiar with the test procedures, as they regularly performed them as part of their routines. The various questionnaires administered to the players were explained beforehand, and any doubts were resolved to clarify and standardize their completion. With respect to training, both teams engaged in the same structured training program for the same duration. Anthropometric Measures. Anthropometric measurements were taken following ISO 7250-1:2017 [21] and the International Society for the Advancement of Kinanthropometry (ISAK) standard [17]. The following measurements were taken: two basic measures (body mass and height), six skinfold thicknesses (triceps, subscapular, supra-iliac, abdominal, thigh, and calf), and three circumferences (arm relaxed, waist, and hip). An inextensible metal tape CESCORF (CESCORF, Porto Alegre, Brazil) was used to measure circumferences, and a Holtain mechanical caliper (HOL-98610 ND) with an accuracy of 0.2 mm was used for skinfold measurements. All anthropometric measurements were taken two or three times, depending on whether the technical measurement error (TEM) between the first two measurements was greater than 5% in skinfolds and 1% in other measurements, taking the mean or median, respectively, for subsequent analysis. This ensures that the collected data are precise and consistent, which in turn guarantees the validity of the research results and allows for accurate interpretation of observed differences between measurements. The room temperature where the measurements were taken was standardized at 24 \({}^{\circ}\)C. Body composition was determined using equations described in the consensus document of the Spanish Group of Kinanthropometry of the Spanish Federation of Sports Medicine [22], following the four-component model (MM, FM, BM, and residual mass (RM)). The following equation was used: Faulkner [23] to calculate FM expressed as a percentage. Two health indicators were calculated: waist-hip ratio and BMI. Questionnaires. 24-Hour Recall Questionnaire (R24h): this retrospectively collects and quantifies the intake of foods and beverages consumed during the 24-h period prior to or on the day before the interview.