Preliminary studies in humans suggest that the presence of lipids in the gut can modify glucose absorption. The overall hypothesis of this proposal is that long chain fatty acid sensing in the duodenum has a significant role in modifying nutrient (glucose and amino acid) absorption from the GI tract through a gut-brain-gut axis.

The investigator will conduct a study in 20 lean (BMI = 19-27 kg/m2) subjects involving intravenous (IV) and intraduodenal (ID) infusions of glucose tracers or amino acid tracers and measurement of tracer rate of appearance in the plasma. An ID infusion of LCFA will allow the investigators to determine if LCFA can alter nutrient absorption and glucose and amino acid metabolism. Benzocaine will be added to the ID infusion of LCFA to inhibit nerve terminals in the duodenum thereby preventing gut-brain communication. Plasma levels of glucose and amino acid tracers, glucose oxidation (13CO2 breath test), gut hormones (CCK, GIP, PYY, GLP-1, ghrelin), and bioactive lipids (N-acyl phosphatidylethanolamines, NAPEs) will be measured during all infusion periods.

Inclusion Criteria:

• BMI = 19-27 kg/m2
• 30-55 years of age

Exclusion Criteria:

• Contraindication for nasal tube placement (e.g. deviated septum, prior upper gastrointestinal bleed, or history of easy bleeding)
• Prior gastric or intestinal surgery or pancreas resection
• Females with a positive pregnancy test
• Known history of intestinal diseases including (but not limited to) inflammatory bowel disease (e.g. ulcerative colitis, Crohn's disease), celiac sprue, Barrett's esophagus
• Type 1 or type 2 diabetes
• Gastroenteritis (diarrhea and/or vomiting) or constipation within the past week