GLP-1 and GIP are incretins which are produced in the intestinal mucosa and are normally secreted when food is eaten in order to reduce glycaemic exclusion by causing an increase in insulin secretion. These incretins are involved in the early stage of the insulin secretory response however the plasma insulin response is also influenced by hepatic insulin extraction which GLP-1 and GIP measurement cannot determine, therefore to optimise this, C-peptide will be also measured in this study.