The main aim of the current study is to investigate whether consuming grapes rich in flavonoids just before mental stress can protect cerebrovascular and peripheral vascular function, mood and cognition, from the negative effects of mental stress in young healthy adults. A second, exploratory aim, will further address whether quality of habitual diet, microbiome health (composition; metabolites production e.g. Short-chain fatty acids) and levels of cardiorespiratory fitness play a role on the beneficial effects of grapes during mental stress. All participants will receive a high-flavonoid grape intervention (60 g freeze-dried grape powder, equivalent to 300 g fresh grapes) and a low-flavonoid grape intervention (60 g powdere isocaloric-matched control). It is hypothesized that the high-flavonoid grape intervention will improve cortical oxygenation and cognitive function in the context of mental stress, and prevent the stress-induced decline in peripheral endothelial function following stress. Furthermore, it is hypothesized that individuals with poorer diets, cardiorespiratory fitness and a poorer gut microbiome will benefit more from the grape intervention in the context of mental stress.

Psychological stress is widespread in our societies, and has been extensively shown to have negative consequences for human health. Specifically, psychological stress induces significant declines in human vascular function, as measured by brachial Flow-mediated Dilatation (FMD). We have demonstrated that flavonoid interventions can prevent the harmful effects of stress on the vascular system. Indeed, flavonoid-rich interventions have also been extensively shown to improve peripheral and cerebrovascular function in the absence of stress. However, the effect of flavonoids on cerebrovascular function and cognition in the context of mental stress is unknown. In the proposed project, our key objectives are to investigate whether grape intake prior to a mental stress task results in better brain oxygenation and vascular function, which leads to improved cognitive performance and mood in young healthy adults. These data will establish whether grapes can be effective as a 'stress snack' to optimize cognitive and brain function in the context of psychological stress. Furthermore, we will explore whether there are certain participant characteristics that mediate the impact of grape flavonoids on cerebrovascular function and cognition in the context of mental stress. Such as, physical fitness (assessed by a VO2 max test), composition of gut microbiome (assessed by faecal sample), habitual diet (assessed by 3-day food diary and the food frequency questionnaire), and eating behaviour and chronic stress (assessed by the eating behaviour questionnaire and perceived stress scale). This work will be important to guide future dietary recommendations around stress and might ultimately result in increased intake of flavonoid-rich grapes and other flavonoid-rich fruits/vegetables overall.

Inclusion Criteria:

• Males and females
• 18 - 40 years old

Exclusion Criteria:

• Smokers
• Consumes > 21 units of alcohol per week
• History of cardiovascular, respiratory, metabolic, liver or inflammatory diseases
• Suffers from blood-clotting disorders
• Allergies or intolerances to foods
• On a weight reducing dietary regiment
• Currently taking dietary supplements, including fatty acids and vitamins
• On long-term medication or have been on antibiotics in the last 3 months
• Has an infection at present (e.g. cold) or viral infection

The interventions have been masked by the intervention supplier (California Table Grape Commission). Therefore, all researchers are blinded to the conditions.