 Participants will be asked to provide informed consent to participate in the study and to answer a number of questions to confirm that it is safe for them to do so, and to confirm eligibility. Participants will be asked to monitor their diet for 48 h before their first laboratory visit, and then to replicate this diet before subsequent visits. Participants will also be asked abstain from caffeine i.e tea and coffee, alcohol and strenuous physical activity the day before visiting us e.g. no exercise that causing sweating or heavy breathing. 