['gastroparesis', 'diabetes mellitus']
['sitagliptin', 'placebo']

        Inclusion Criteria:

          -  Type 2 diabetes (World Health Organisation (WHO) criteria), managed by diet or
             metformin alone

          -  Body mass index (BMI) 20 - 40 kg/m2

          -  Males and females (females of reproductive potential must be using an appropriate
             contraceptive method)

          -  Glycated haemoglobin (HbA1c) ≤ 8.5%

          -  Haemoglobin above the lower limit of the normal range (i.e. >135g/L for men and 115g/L
             for women), and ferritin above the lower limit of normal (i.e. >10mcg/L)

        Exclusion Criteria:

          -  Subjects with gastrointestinal disease, significant upper or lower gastrointestinal
             symptoms, or previous gastrointestinal surgery (other than uncomplicated
             appendicectomy or cholecystectomy)

          -  Other significant illness, including epilepsy, cardiovascular or respiratory disease.

          -  History of unexplained pancreatitis, chronic pancreatitis, pancreatectomy.

          -  Impaired renal or liver function (as assessed by calculated creatinine clearance < 50
             mL/min using the Cockroft-Gault equation (27) or abnormal liver function tests (> 2
             times upper limit of normal range)).

          -  Requirement for medication known to influence blood pressure and/or heart rate and/or
             gastrointestinal function, drugs with anticholinergic effects

          -  Alcohol consumption > 20 g per day

          -  Smoking > 10 cigarettes per day

          -  Pregnancy or lactation.

          -  Vegetarian

          -  Allergy to sitagliptin or any other 'gliptin'.

          -  Donation of blood within the previous 3 months

          -  Participation in any other research studies within the previous 3 months

          -  Exposure to ionising radiation for research purposes in the previous 12 months

          -  Inability to give informed consent
      