A nutritional intervention within highly trained youth soccer players using a COM-B model of behaviour change: a case series approach

Large inter-individual variability in daily energy and carbohydrate intake has been reported in highly trained academy soccer players, potentially impacting training and match-day performance, recovery and physical development. Nutritional interventions in these cohorts typically rely on group education without behaviour change theory, limiting their long-term effectiveness. Consequently, this study aimed to improve the nutritional intake of highly-trained youth soccer players via an individualised, theory-driven dietary behaviour change programme. This mixed method case series utilised the COM-B model and Behaviour change wheel (BCW) to design and implement an eight-week dietary behaviour change programme in three full-time (16.7 ± 0.3 years) academy players (P1; P2; P3). Education and enablement were used to improve players' understanding of their energy and macronutrient requirements, alongside training to develop practical nutrition skills. Environmental restructuring was used to modify player’s physical environment, ensuring they had appropriate food when away from the club. Daily energy intake increased by 55%, 19% and 24% for P1, P2 and P3, respectively, corresponding with DXA-derived fat-free mass gains of 1.4, 0.5 and 0.3kg. Absolute carbohydrate intake increased by 217, 78 and 110g.day-1 respectively, alongside improved fuelling practices around match day. Qualitative insights uncovered improvements in nutritional knowledge and cooking skills (Psychological and Physical Capability), while a desire to improve physical characteristics (Reflective Motivation) was a key adherence factor. The COM-B model and BCW provided a structured framework for designing an effective dietary behaviour change programme that successfully improved dietary behaviours in three highly trained youth soccer players.