This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Flow-mediated dilation (FMD) of the brachial artery using high-resolution ultrasound is a well accepted non-invasive bioassay for in vivo endothelium-generated nitric oxide (NO) in humans. NO has been characterized as a potent vasodilator, but NO also has a considerable role in maintaining healthy endothelium and inhibiting key steps in the development, progression, and clinical manifestations of atherosclerosis. The postprandial state may be critical in the development of atherosclerosis. Diets high in cereal fiber have been linked to reduced risk of cardiovascular disease. Conversely, high-glycemic index (GI) diets have been linked to increased cardiovascular mortality. We postulate that the beneficial effect of cereal fiber on FMD is stronger than the potentially adverse effect of GI. Therefore, we hypothesize that breakfast meals high in cereal fiber will acutely improve FMD, regardless of GI. By contrast, we hypothesize that a high-GI breakfast meal that is low in cereal fiber will impair FMD. We also hypothesize that a breakfast meal that is low in both GI and cereal fiber will have no effect on postprandial FMD. Brachial artery flow-mediated dilation (FMD) will be assessed before and at 2 h and 4 h after each of four breakfast meals [(1) High-fiber, Low GI; (2) High-fiber, High-GI; (3) Low-fiber, Low-GI; (4) Low-fiber, High-GI] using high-resolution ultrasound and edge-detection software in healthy adults ages 18-64. Analysis of variance with repeated measures will be used to assess differences in FMD in response to the meal challenges.