Background and aim:
Previous studies with high-dose nitrate or L-arginine supplementation have shown to improve postprandial vascular endothelial function, via their effects on nitric oxide bioavailability. Nutritional supplements containing lower and more feasible amounts of both nitrate and L-arginine might have more potential in improving postprandial endothelial function. Therefore, the aim of the present study was to compare effects of beetroot powder with or without L-arginine on postprandial endothelial function, as assessed by brachial artery flow-mediated vasodilation (FMD), after consumption of a high-fat mixed-meal in apparently healthy abdominally obese men.

Methods:
This randomized, double-blinded, cross-over trial consisted of five test days, each separated by a wash-out period of at least one week. Eighteen men with a waist circumference between 102.4 and 129.0 centimeters completed all five test days. On each test day, men received a high-fat blended meal (55.3 grams of fat) with (i) beetroot powder providing 200 mg nitrate, (ii) beetroot with 0.8 grams of L-arginine powder, (iii) beetroot with 1.5 grams of L-arginine powder, (iv) 3.0 grams of L-arginine powder, or (v) a control supplement. Brachial artery FMD measurements were performed fasted and 2-hour post-consumption.

Results:
The control supplement significantly decreased postprandial FMD (P = 0.026), however, postprandial FMD values were not significantly different between meals (meal effect, P = 0.45). A trend for a more beneficial postprandial FMD value was observed for the beetroot-containing meals as compared with meals without beetroot (P = 0.074). Postprandial baseline brachial artery diameters, blood pressure, lipemia or glycemia were not significantly changed.

Conclusion:
In apparently healthy abdominally obese men, a single dose of beetroot powder with L-arginine powder did not differently affect postprandial endothelial function. However, a trend was found for a smaller decrease in postprandial endothelial function with meals containing beetroot powder compared with meals containing no beetroot powder.