Recent studies in both animals and humans has demonstrated that the hormone GLP-1 (glucagon like peptide 1) reduces intestinal production of lipoprotein particles. The investigators therefore hypothesise that the drug sitagliptin which prevents the breakdown of GLP-1 will reduce intestinal lipoprotein production in humans. The investigators are unable to speculate whether sitagliptin will affect hepatic lipoprotein production because of lack of of data from animal studies or in vitro data. Sitagliptin is already an approved treatment for type 2 diabetes.

Each subject will be studied twice 4-6 weeks apart in random order in this single blinded study. In study A they will receive a single dose of sitagliptin 100mg od. In study B they will receive placebo. A nasoduodenal tube will be sited under fluoroscopic guidance the day prior to the study. On the day of the study regular liquid formula (Great shake plus) will be infused from 4am through the tube to maintain a constant fed state. A pancreatic clamp (octreotide with replacement glucose, insulin and growth hormone) along with saline/sitagliptin will be started at 7am. From 9am an iv bolus of deuterated-glycerol (d5-glycerol) along with a regular infusion of deuterated leucine (L-[5,5,5-2H3]. Regular blood samples will be drawn to assess lipoprotein kinetics.

Inclusion Criteria:

1. Men and women, aged 18 to 60 years
2. Body mass index 20 kg/m2 to 27 kg/m2
3. Hemoglobin above 130g/L.
4. Normal glucose tolerance in response to a 75g, 2-hr OGTT

Exclusion Criteria:

1. Subject has a history of hepatitis/hepatic disease that has been active within the previous two years.
2. Any significant active (over the past 12 months) disease of the gastrointestinal, pulmonary, neurological, renal (Cr > 1.5 mg/dL), genitourinary, hematological systems, or has severe uncontrolled treated or untreated hypertension (sitting diastolic BP > 100 or systolic > 180) or proliferative retinopathy
3. History of diabetes or OGTT indicative of diabetes or impaired glucose tolerance.
4. Any history of a MI or clinically significant, active, cardiovascular history including a history of arrhythmia's or conduction delays on ECG, unstable angina, or decompensated heart failure.
5. Any laboratory values: AST > 2x ULN; ALT > 2x ULN TSH > 6 mU/l
6. Current addiction to alcohol or substances of abuse as determined by the investigator.
7. Mental incapacity, unwillingness or language barrier precluding adequate understanding or cooperation
8. Taking any prescription or non-prescription medications at the time of the study
9. Having donated blood three months prior to and three months post study procedures
10. A pregnancy test will be performed 1 to 3 days prior to each study in all female subjects. Those who test positive for pregnancy will be excluded.

10 hours