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It is well documented that eating a regular breakfast is associated with benefits to markers of metabolic health and cognitive performance. The composition of breakfast differentially affects the metabolic response which may also have implications for cognitive performance. To date, much of the research on gluco-regulation is in adults, and no studies have investigated the effects of a functional-food breakfast (FB) on gluco-regulation and cognitive performance, mood and satiety in adolescents. Therefore, this thesis aims to address this research gap through the implementation of a series of five research studies. The primary aim was to investigate the effects of a FB which included ingredients selected for their potential to improve gluco-regulation (blueberries, baobab, cinnamon and oats) on measures of gluco-regulation (glucose response (GR) and insulin response (IR)) compared to a control breakfast (CB), and ready to eat cereal (RTEC) (adults only). Secondary aims were to measure: cognitive performance (using a map recall and delayed word recall task), mood (using the 'Activation–Deactivation Check List’) and satiety (using VAS scales). Measures were collected at timed intervals over a three-hour period after the three breakfasts. The study was first implemented in healthy adults (n=16, 32.0±10.0 years) in a controlled laboratory environment and found that consumption of the FB resulted in a lower glucose peak and a lower IR AUC, compared to the CB and RTEC (p < .05) (chapter 6). In a school environment, adolescents' (n=22, 13.7±0.5 years) consumption of the FB reduced peak glucose, peak insulin and IR AUC at 60 and 120 minutes, compared to the CB (p < .05) (chapter 7). There were no effects on cognitive performance, mood or satiety regardless of breakfast condition (p >.05). Two preliminary studies (chapter 3 and 4) contributed to aspects of the FB and CB development (chapter 5) and breakfast study design (chapter 6 and 7). In chapter 3, validation of a novel portable indirect calorimeter in adults (n=20, 38.3 ±11.2 years) resulted in the revision of the main hypothesis (chapter 2), where investigations into the effect of the FB on energy expenditure (EE) was discontinued. In chapter 4, the completion of a breakfast-based questionnaire by adolescents (n=434, 13-15 years) informed the choice of ready to eat cereal (RTEC) on which the breakfast conditions were based (chapter 5). Additionally, these studies made individual contributions to the literature reporting the use of indirect calorimetry in schools to collect body composition measures from adolescents (n=30) (chapter 3) and highlighting implications for the design of breakfast interventions in adolescents (chapter 4). Findings from this thesis suggest that the addition of functional food ingredients to breakfast has the potential to improve gluco-regulation in healthy adults and adolescents. The inclusion of functional food ingredients as part of breakfast should be considered alongside the promotion of breakfast.