Participants are hospitalized for 12 days. They are randomly assigned to take one of the following four treatments for 10 days: 1) 200 mg of GW873140 once a day, or placebo (a look-alike pill with no active ingredient); 2) 200 mg of GW873140 twice a day, or placebo; 3) 400 mg of GW873140 once a day, or placebo; or 600 mg of GW873140 twice a day, or placebo. Participants record the meals they eat on a diary card. In addition, they undergo the following tests and procedures: