Beetroot juice appears to improve endurance and speed in male soccer players, according to a recent study. Earlier research had shown benefits for other athletes, including swimmers and cyclists. The players drank about 4.7 ounces of nitrate rich beetroot juice (providing about 800 milligrams of nitrates per day) or an equal amount of nitrate depleted juice for six days. Those who drank the nitrate rich juice saw 3.4 percent improvement on a high-intensity, intermittent running test compared to the other group of players. Their heart rates were also lower.
Source: “Beetroot Juice Supplementation Improves High-Intensity Intermittent Type Exercise Performance in Trained Soccer Players” by J. Nakayiru et al.,Nutrients 3/22/17