 Study days: Forty - eight hours prior to each study day, participants will begin dietary restrictions. Participants will then attend the first study day following an overnight fast. A cannula will be inserted and baseline blood samples obtained, baseline measures of cerebral blood flow will be examined using near infrared spectroscopy and its effect on cognitive function using a cognitive demand battery. The relevant drink will then be provided and blood samples and blood flow measures will be taken at hourly intervals 1, 2, 3, and 5h. No additional food or drink will be provided during the study period except for low-nitrate mineral water. After a minimum of 2 weeks, participants will be asked to return to the lab and repeat the procedure with the other drink. 