Original article written by Matthew North, Adam Kelly, Mayur Ranchordas, and Matthew Cole.
Background
Due to growth and maturation, young athletes undergo many anatomical and physiological changes during the first two decades of life and applying nutritional guidelines for adult athletes to young athletes is therefore not appropriate. Young athletes are a unique population and provide challenges for practitioners as they experience periods of rapid and non-uniform growth in skeletal structures. Highly variable rates of growth and maturation between young athletes, particularly around peak height velocity, will influence energy requirements. Furthermore, training load has been shown to increase with age and maturation in young athletes [1], and this will alter the nutritional requirements.
Nutritional recommendations for young athletes should not only focus on sporting performance but also meet the requirements for optimal growth and development. The importance of ensuring that young athletes understand their nutrition is that insufficient energy intake has been shown to result in body and muscle mass loss, injury, illness, increased prevalence of overtraining, and severely impaired performance [2].
What the authors did
The authors conducted a systematic review, where relevant journal articles were searched for in databases using key terms, included or excluded based on specific criteria, and then rated for quality. The final papers included were then used to draw conclusions on the nutritional considerations for youth soccer players.
In the current study, the authors searched the electronic databases of MEDLINE and SPORTDiscus in November 2020. The search terms used in the database were as follows: (“football” OR “soccer”) AND (“Academy” OR “Youth” OR “adolescent” OR “young athlete”) AND (“Nutrition” OR “energy expenditure” OR “energy Intake” OR “dietary” OR “Nutritional”). The inclusion criteria were: (a) original research (not abstract or reviews); (b) assessed academy aged (U9 to U23) players in a high-performance youth soccer setting; (c) investigated an element of nutritional status, knowledge, or intervention; and (d) available in English. The initial search found 471 studies once duplicates had been removed, and the final number of studies included following screening was 53.
What the authors found
The systematic review found very few studies that investigated energy expenditure in your soccer players. However, a study from Hannon et al. [3] reported total energy expenditure values of 2859 ± 265 kcal/day (range: 2275–3903 kcal/day), 3029 ± 262 kcal/day (range: 2738–3726 kcal/day), and 3586 ± 487 kcal/day (range: 2542·5172 kcal/day) for U12/13, U15, and U18 EPL players, respectively. Findings from the review suggest that studies have consistently reported energy intake is inadequate in relation to estimated energy expenditure in youth soccer players. A study in Italian young players reported findings displaying mean energy deficits of up to − 890 ± 734 kcal/day [4].
In general, as players progress through age groups, they do not increase their energy intake sufficiently to meet the increased energy requirements. Absolute energy intake appears to be consistent irrespective of age between the U13s to U20s. However, when expressed in relative terms to body weight, a reduction in overall energy intake is observed as players progress through age groups, with data from English Premier League academy players highlighting relative energy intake to body weight being: U12/13 (68 ± 8 kcal/kg/day), U15 (50 ± 7 kcal/kg/ day), and U18 (44 ± 7 kcal/kg/day) [3]. Furthermore, current evidence suggests HPYS players do not periodise their energy intake and specifically carbohydrate intake to match the demands of training and competition. Findings in U16 Portuguese players showed larger energy deficits of − 1030 kcal/day and − 1009 kcal/day on heavy training and match days respectively [5].
There has been limited research into protein intake and requirements for young soccer players. However, protein requirements of 1.4 g/kg/day have been suggested [6], which are higher than recommend daily allowances but in-line with guidelines for adult athletes [7]. The authors of the current study concluded that all studies included in the systematic review investigating nutritional intakes demonstrated players met or exceeded their protein requirements based on the current guidelines [8].
However, from a carbohydrate point of view, players do not appear to be meeting their energy requirements (particularly in older age groups). Findings of this review suggest players currently consume between 5 and 7 g/kg/day carbohydrate daily with the majority currently around 5 g/kg/day; irrespective of age or nationality, which means youth players are only just meeting the lower end of adult soccer player recommendations, ranging between 5 and 10 g/ kg/day [9]. Some players in English Premier League academies consumed inadequate daily CHO, with values as low as 3.2 g/kg/day [10]. Of further concern is the findings within the older age groups, showing CHO intake relative to body mass decreases as players age.
The largest proportion of goals are conceded during the latter stages of a football match, likely due to the onset of fatigue, which may be due to a reduction in muscle glycogen. Therefore, carbohydrate ingestion during competition has been suggested to reduce decrements in performance and limit the onset of fatigue. When players ingested two 250-ml doses (pre-exercise and at halftime) of a 12% CHO-E solution they showed improvements in passing accuracy in both the early and latter stages of the game, passing speed in the later half, and post-match high intensity running [11].
Considering that children have lower sweat rates compared to adults, coupled with a higher metabolic cost of locomotion, thermoregulation can be harder in children [12]. Thus, hydration is key, since the onset of dehydration can result in greater increases in core temperature. Studies investigating hydration in Brazilian U18s consistently reported that fluid intake did not match fluid losses [13,14]. As expected, higher temperatures posed a greater risk to hydration status even with an increased self-selected fluid intake as sweat rate increased, with six of 20 players losing more than 3 L [14]. Interestingly, studies found players attended matches in a hypo-hydrated state, whereby ~ 45% of the players started the match with a moderate dehydration status, ~ 50% of the players presented a significant level of dehydration, and ~ 5% presented a condition of serious dehydration (USG > 1.030 g/mL) in the pre-match period [15].
Limitations
Through no fault of the authors of this review, there was not enough consistent research to conduct a meta-analysis on this topic. Conducting a meta-analysis would have allowed objective data to be reported, which would include specific values for energy intake and expenditure as well as recommendations. Similarly, there has been a lack of research into the influence of maturity status on energy requirements, with the majority of data being collected on specific age groups. As maturation has a significant influence on energy expenditure, understanding the influence of nutritional requirements is key.
What this means for coaches
This review provides a comprehensive picture of the current status of youth soccer players and their nutrition. The take homes for coaches from this review are that youth soccer players may well be under fuelling, especially from a carbohydrate point of view. It is important to educate players on the need for increased energy intake as they grow and age, to reduce injury risk and improve performance. Furthermore, it is vital that players understand hydration, and that they are encouraged to stay hydrated throughout the week, not just during matches. The study provides evidence of strategies to help combat these issues, that practitioners can implement immediately such aa high carbohydrate pre-match breakfast, and fluid intakes during half time periods.
Reviewer’s comments
A thorough review of a very interesting and important topic area. Eye opening for practitioners about how much players may be under fuelling, and arriving to matches already in a dehydrated state.
Recommended resources
Podcast – Team sport nutrition, half-time refueling strategies and pre-season vs in-season fueling – Mark Bubbs
Podcast – Nutrition for the S&C coach – James Morehen
Live – Sports performance nutrition – James Morehen, Hannah Sheridan and Graeme Close