The PRE-OP ENERGY Trial

Inclusion Criteria: ALL of the following: * Adult cardiac surgery patients (≥18 years) undergoing cardiac surgery (CABG, Valve, or CABG and Valve) with cardiopulmonary bypass. * BMI\<30 * Able, in the opinion of the investigator, and willing to give informed consent. * Do not have diagnosed coeliac disease * Able to understand English Exclusion Criteria: Any of the following: * Urgent, emergency or salvage procedure * Patients with end stage renal failure defined as an estimated Glomerular Filtration rate (eGFR) \<15 mL/min/1.73 m2 calculated from the Modification of Diet in Renal Disease equation,1 or patients who are on long-term haemodialysis or have undergone renal transplantation. * Patients with persistent or chronic atrial fibrillation. * Patients with severe liver dysfunction; hepatitis, cirrhosis, jaundice. * Women who are pregnant or who may become pregnant in the intraoperative period. * Patients who are participating in another interventional clinical trial. * Unable, in the opinion of the investigator, or unwilling to give informed consent. * Have diagnosed coeliac disease * Unable to understand English Exclusion criteria for optional MRI research procedure: * Permanent pacemaker or ICD * Brain Aneurysm Clip * Implanted neural stimulator * Cochlear implant (specific implant must be checked that it is MR safe) * Ocular foreign body (e.g. metal shavings) unless removed * Other implanted medical devices: (e.g. Swan Ganz catheter) * Insulin pump * Retained met…