One of the first researchers to take note of beets potential for exercisers was Andrew Jones, PhD, an applied physiology professor at the University of Exeter in the U.K. In 2007, his interest was piqued by a small study in which researchers supplemented participants’ diets with nitrate, a molecule found in green, leafy vegetables and beets. In two separate three-day trials, nine men consumed a small amount of nitrate (achievable by consuming a balanced diet rich in vegetables), while a control group received salt supplements as a placebo. Researchers then examined the subjects while they cycled. Those who consumed nitrate required less oxygen while exercising. “It suggested the muscle had become more efficient,” Jones says.

For his own study, published in 2009, Jones used beetroot juice as the source of nitrate. For six days, eight men either drank 500 milliliters of beetroot juice or another dark drink as placebo. Jones then put people through moderate-intensity and high-intensity cycling exercises. During the moderate-intensity session, the men who drank beet juice needed 19% less oxygen to perform the task. Beet juice drinkers were also able to perform the high-intensity cycling exercise for longer until they hit exhaustion, “suggesting performance was enhanced,” Jones says, though the study was too small to be known for certain.

Following Jones’ 2009 study, research began to pile in supporting beetroot’s efficacy in sports. In 2011, Jones and his team at the University of Exeter examined cyclists who drank beetroot juice two-and-a-half hours before a competition and found those who drank the juice had improved speed and stroke power. They also determined that rugby, hockey, and soccer players who drank beet juice for seven days prior to a match were more likely to make faster decisions on the field in addition to enhancing sprinting performance in a 2015 study.

The nitrates found in beets are likely the key to these positive results. When people eat food rich in nitrates, the bacteria inside the mouth converts the nitrate into nitrite, Jones explains. When the nitrate is swallowed, it’s converted into nitric oxide. “Nitric oxide is a molecule that causes blood vessels to dilate, so it can alter blood pressure, it can change blood flow to tissues, including muscles,” Jones says. “But it also acts within muscle cells that make mitochondria that produce energy aerobically, and work more efficiently. It can also impact aspects of our muscle cells, to enable contraction to occur stronger and faster.”

While nitrates are naturally found in foods like celery, lettuce, radishes, carrots, spinach, and arugula, researchers tend to use beetroot juice for their studies because “it’s easier to swallow 150 milliliters of a fluid than it is to eat a plate of spinach,” Jones explains (and because beets tend to have slightly higher levels of nitrates).

Dozens of research ventures have used beetroot juice to further explore the effects of nitric oxide in athletic functions — and in the process, beet juices and powders have become popular among runners.

In a 2017 review of scientific research, scientists surmised that adding beetroot juice to athletes’ diets could “improve cardiorespiratory endurance in athletes by increasing efficiency,” improve performance at various distances, and help stave off exhaustion. A study from 2018 found beetroot juice supplements helped both professional and recreational athletes accelerate faster in sprint cycling and skating exercises. Consuming about 70 milliliters of beet juice per day for a week leading up to a competition, including the morning of, seems to be the most effective for athletes, Jones says.

Andrew R. Coggan, PhD, an exercise physiologist and associate professor at Indiana University-Purdue University Indianapolis is unsure if consuming carrot or celery juice — foods also high in nitrates — would produce the same effect in athletes. “I have seen a couple of studies of blood pressure that have used spinach or mixed greens, and the results are comparable to drinking beet juice,” he says.

Yet endurance athletes continue to hold stock in beets. Because initial research showed nitrates in beets improved exercise economy — the amount of oxygen required to perform an activity — “the automatic thought was that it’s likely to improve endurance performance,” Jones says. “Whether that’s shorter term higher intensity endurance performance or lower intensity endurance performance has not been teased out.”

As for highly trained endurance athletes, they may just need more doses of beet juice to feel a significant effect, per a study from earlier this year. Jones also believes briefly depriving your body of nitrates and reintroducing the molecule in the days leading up to an event could allow for a greater impact, though this theory has only been studied in rats and he wouldn’t yet recommend humans try this method.