The game of soccer places various physiological demands on players, who are required to respond by carrying out a range of locomotor activities at different intensities. Such activity patterns contribute to a high energy turnover in both training and match-play, which in turn requires the intake of adequate fuel sources to sustain it. Adequate nutrient intake constitutes an important foundation for physical performance by providing fuel for biological work, both short and long term as required throughout the course of a soccer match. Despite the popularity of the sport worldwide, few studies investigating the effect of nutrition on performance in soccer have been conducted to substantiate the effect of optimal nutrition over the duration of a standard soccer match. This dearth of evidence has contributed in turn to a lack of specific nutrition guidelines for soccer players, coaches, sport scientists, nutritionists and club administrators. The aim of this thesis is to investigate the physiological, psychological and sociological aspects of nutrition and soccer, and posit a comprehensive nutritional framework to actively engage soccer players in adopting diets supportive of optimal performance in soccer training and match-play. The researcher set out by hypothesising that an optimal diet positively influences physical performance in soccer match-play. To test this hypothesis, a 90 h diet was developed for the participating semi-professional soccer players. Following implementation of the diet, a 90-minute soccer-specific simulation protocol, BEAST90mod was used to test its effects on physical performance in soccer. The remaining three inter-linked studies were longitudinal in nature, and carried out with participants forming part of the Malta U21 National Soccer Team. In the first instance, players' habitual dietary intake, expenditure and energy balance was examined. The researcher then gathered information about the players' knowledge, attitudes, habits, perceptions and barriers towards a diet conducive with optimal soccer performance. The same players finally underwent a 9-month nutritional education and support intervention, the efficacy of which was measured by the researcher throughout the intervention period. The principle aim of the research is to present findings that provide players and stakeholders in soccer a clear indication of the effects of specialist nutrition in soccer, and empower them with a range of appropriate tools and strategies as employed throughout the support programme. It ultimately seeks to improve physical performance in soccer training and match-play by informing sound individual and team approaches to nutritional decision-making.