The purpose of this study is to measure the effect of quercetin on glucose tolerance and postprandial endothelial function in comparison to placebo and Acarbose in participants with Type 2 Diabetes.

Primary Hypothesis: We hypothesize that administration of quercetin (2g oral) prior to a 100g maltose tolerance test (MTT) will result in a decrease in postprandial blood glucose at 60 minutes compared to placebo. Acarbose (100mg oral), a pharmaceutical alpha-glucosidase inhibitor, will serve as a positive control.

Secondary Hypothesis: We hypothesize that administration of quercetin (2g oral) will reduce the Area Under the Glucose Curve (AUC) for the 2 hours following a 100g MTT compared to placebo. AUC is hypothesized to be comparable between quercetin and Acarbose.

Tertiary hypothesis: We hypothesize that administration of quercetin (2g oral) prior to a 100g MTT will result in a smaller reduction in flow mediated dilation (FMD) measured as an increase in Reactive Hyperemia Index (RHI) at 90 minutes compared to placebo.

This is a phase II, crossover, double-blinded, controlled trial in 20 participants with type 2 diabetes designed to measure the effect of quercetin on glucose tolerance and postprandial endothelial function in comparison to placebo and Acarbose. Glucose tolerance and insulin excursion will be measured at 0, 30, 60, and 120 minutes following a 100g maltose tolerance test (MTT). Each participant will blindly rotate between three single individual doses of placebo, quercetin (2g oral), and Acarbose (100mg oral) prior to the MTT on 3 separate occasions. Each participant will serve as their own control and comparison for each of the interventions.

Fasting and post-MTT endothelial function will be measured by peripheral tonometry (Itamar EndoPAT (Peripheral Arterial Tone) 2000) and reported as reactive hyperemia index (RHI). EndoPAT testing will be performed prior to the fasting blood collection and then again at 90 minutes following the MTT, during each clinical research visit.

Exploratory data will also be collected on post-MTT increases in gamma-glutamyltransferase (GGT).

Inclusion Criteria:

• Adults aged 18-75 years with the International Classification of diseases book 9 (ICD-9) diagnosis of type 2 diabetes (250.XX). As lack of clarity in ICD-9 coding by providers is notorious in type 2 diabetes, we will specify ICD-9 diagnosis 250.XX in order to capture all subtypes of type 2 diabetes (see ICD-9 book for more information on subtypes).
• Patients on a stable dose (consistent dose for one month) of all medications and supplements.
• Hemoglobin A1c (HbA1c) of 6.5-10.5% within the last year. Since quercetin's effect on blood sugar and endothelial function may be related to its anti-oxidant properties, we are interested in looking at is effect on patients with higher levels of oxidative damage associated with higher blood sugars (i.e. elevated HbA1c > 6.5%), yet we will exclude those with severe hyperglycemia.
• Stable exercise and diet for last 1 month.
• Labs (HbA1c, aspartate aminotransferase (AST), Alanine transaminase (ALT), Glomerular filtration rate (GFR), and creatinine) measured within the last year and meet inclusion/exclusion criteria or we will run them.

Exclusion Criteria:

• Current use of insulin or Acarbose (due to possible hypoglycemia); insulin exclusion will ensure exclusion of those with type 1 diabetes.
• Current use of quercetin.
• History of myocardial infarction within the last 6 months, angina, ischemic stroke, uncontrolled hypertension with systolic greater than 180 or diastolic greater than 110.
• Clinical or objective finding suggestive of congestive heart failure Class III or IV or shortness of breath with Activities of Daily Living (ADLs).
• Recent (<14 days) history of infection. During the telephone screening, if patients have had an acute infection in the last 14 days they will be asked if we may recontact them in 3-4 weeks for a second telephone screening to determine qualification (including resolution of their recent infection > 14 days).
• Stage IV or higher kidney disease (eGFR < 30).
• Liver disease (defined as AST or ALT > 2 x high normal (according to lab range)).
• Prior diagnosis of genetic abnormalities of carbohydrate metabolism (e.g. Congenital Sucrase-Isomaltase, Pompe Disease).
• Pregnant or breast feeding.
• Mental illness or other cognitive impairment prohibiting the candidate from making an informed choice (determined at the discretion of the PI in consult with the Research Assistants/Study Coordinator as needed) as assessed throughout telephone screening and informed consent process.
• Hypersensitivity to quercetin or Acarbose; based on past allergic symptoms taken with either drug or drug or supplement.
• Diagnosis of celiac disease/"sprue".
• Contraindications for EndoPAT:
• Participants on anti-platelet medications will be excluded if they have visible bruising (beyond petechiae).
• Participants will be excluded if they are unwilling to fast for 12 hours prior to maltose tolerance test and/or EndoPAT.
• Participants will be excluded if they have taken nitroglycerine, Cialis, or Viagra 12 hrs before test days.
• In order to accommodate the finger probes, participants will be excluded if they are unwilling to clip their fingernails on their index finger short prior to test days. Index finger nail must not extend past their finger on test days.
• Bilateral upper extremity lymphedema.
• Contraindications for Acarbose:
• Current diabetic ketoacidosis.
• Inflammatory bowel disease; colonic ulceration; partial intestinal obstruction, or in patients predisposed to intestinal obstruction; chronic intestinal diseases with marked maldigestion or malabsorption; hernia.
• Cirrhosis
• Renal impairment (serum creatinine > 2 mg/dL).