In this study, the investigators aimed at evaluating the role of bitter taste receptors in the gastrointestinal tract (GIT). Intragastric or intraduodenal administration of denatonium benzoate (DB) or quinine hydrochloride were compared with placebo administration for their effects on lingual sensitivity, gastrointestinal motility (both in the fasted and fed state), gut hormone release (motilin, ghrelin, glucagon-like peptide-1 (GLP-1) and cholecystokinin (CCK)) and food intake. Differences between lean and obese subjects will be evaluated.

Inclusion Criteria:

• BMI>30 kg/m² for the obese volunteers
• BMI<30 kg/m² for the lean volunteers
• Subject is capable and willing to give informed consent
• Female volunteers of child bearing potential must use oral, injected or implanted hormonal methods of contraception

Exclusion Criteria:

• Female volunteer is pregnant or breastfeeding
• Gastrointestinal diseases, major abdominal surgery
• Major psychiatric illnesses
• Volunteers that use drugs affecting the GIT or the central nervous system (CNS)
• Volunteers that suffer from diabetes mellitus
• Volunteers suffering from an endocrine disease such as diabetes, Cushing's disease, Addison's disease, hypothalamic tumor…
• Volunteers that have undergone surgical procedure for weight loss