The study will compare Concord grape juice to a beverage that contains no grape flavonoids, but has a similar appearance and taste (placebo juice). A total of 60 overweight and obese participants over age 50 will be enrolled. Each participant will drink each beverage for 4 weeks with a 2-week rest period between two beverage consumption periods. The order of beverages (grape juice first or placebo juice first) will be randomized. The investigators will use ultrasound to measure brachial artery flow-mediated dilation, a measure of endothelial vasodilator function. The investigators will also collect blood samples to further assess the cardiovascular effects of grape juice.

The aim of the study is to determine whether Concord grape juice improves endothelial function in patients at risk who do not have cardiovascular disease and may provide information that would guide dietary recommendations. The results may also be used by the sponsor to substantiate claims and labeling of their product.

Inclusion Criteria:

• Body mass index ≥ 25 and < 40 kg/m2
• Age ≥ 50 years
• Otherwise healthy

Exclusion Criteria:

• Clinical diagnosis of atherosclerotic vascular disease.
• Clinical history of diabetes mellitus or fasting glucose ≥126 mg/dl
• Uncontrolled hypertension
• Treatment with an investigational new drug within the last 30 days
• Clinical history of other major illness including end-stage cancer, renal failure, hepatic failure, or other conditions that in the opinion of the principal investigator make the study inappropriate
• Psychological illness or condition such as to interfere with the subject's ability to understand the requirements of the study
• Use of Vitamin E, Vitamin C, beta carotene, lipoic acid, or other food or herbal supplements within 1 month of enrollment. Subjects taking multivitamins or other forms of vitamin E and C in doses that do not exceed two times the recommended daily allowance will not be excluded
• Extreme dietary habits (i.e. Atkins, very high protein/low carbohydrate, or vegan diet