Investigating the Use of Quercetin on Glucose Absorption in Obesity, and Obesity With Type 2 Diabetes

Quercetin is a compound naturally found in various foods. It may have some role in the treatment of obesity and diabetes. The purpose of this study is to investigate research volunteers with obesity or obesity with type 2 diabetes to determine whether quercetin affects the way glucose is absorbed by the body. Thirty two participants aged 19 to 65 who are considered to be medically obese or obese with type 2 diabetes will be enrolled in this study. Before the onset of treatment, they will undergo a medical history, physical exam, blood work, and urinalysis. During the study, participants will be given an oral glucose tolerance test three times; during these tests they will receive 1 or 2 grams of quercetin, or placebo. Researchers will collect blood samples and analyze the effect of the treatment on blood glucose.

Postprandial hyperglycemia and the resultant hyperinsulinemia contribute to the cardiovascular complications seen in obesity and in type 2 diabetes. Epidemiological studies suggest that slow absorption of carbohydrates dampens glucose and insulin peaks, and reduces cardiovascular morbidity. The polyphenol quercetin is the most abundant flavanoid in plant-derived foods, and is sold as a dietary supplement. In vitro, quercetin is a potent and reversible inhibitor of glucose transport by the intestinal glucose transporter GLUT2. In vivo quercetin inhibits post absorptive glucose peaks in obese, diabetic rats. We hypothesize that quercetin blunts intestinal glucose absorption in humans, and attenuates postprandial hyperglycemia. We propose to test, in a double blind placebo controlled study, whether coadministration of 1 or 2 grams of quercetin with glucose will reduce plasma glucose concentrations during a 6 hour oral glucose tolerance test with 3 to 6 grams of 3-O-methyl glucose (3OMG) in non-diabetic obese subjects and in obese type 2 diabetic subjects. The glucose dose may be varied from 0 to 100 grams to better understand the competition between 3OMG and glucose. 3OMG is a non-metabolizable glucose analogue and is excreted unaltered in urine. 3OMG is not found in food and thus glucose absorption can be studies easily without the problem of a high baseline value. The use of 3OMG will provide a more accurate and true measures of glucose absorption. Study subjects will be 19 - 65 years with a body mass index greater than or equal to 30, without complications of diabetes, or on any medication other than oral hypoglycemic agents and aspirin. We will study 16 obese non diabetic subjects and 16 obese type 2 diabetics. Each subject will have 3 oral glucose tolerance tests, and will serve as his or her own control. We will compare the peak plasma glucose concentrations achieved during oral glucose tolerance tests and the area under the curve of plasma glucose to determine whether quercetin inhibits glucose absorption in humans. Such inhibition may partially explain the protective effects of plant derived foods on cardiovascular disease, and enable us to use quercetin or related compounds to dampen intestinal glucose absorption. We will also measure quercetin concentrations in the plasma, in circulating white blood cells and in urine to determine quercetin pharmacokinetics. Additionally, to determine the optimal 3OMG dose, we will study the absorption of glucose and 3OMG, without quercetin, in 12 non-diabetic obese subjects and 12 lean subjects to serve as controls.